ME_Manatee Mining Systems_Design Report REV17

8/7/2019 ME_Manatee Mining Systems_Design Report REV17

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Robotic Lunar ExcavatorME492 Senior Project Detailed Design Report

Mechanical Engineering

Milwaukee School of Engineering

Date: 25 February 2011

Team: Manatee MiningSystemsTeam Advisor: Dr. William

FarrowTeam Members: Rafael Arndt

Jonathan BlockZachary GriffaMichael RileyDavid SwansonMichael VargaRyan WaldmannEugen Zinn


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The Manatee Mining Systems Team would like to extend

appreciation to our sponsors:


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Executive SummaryLunar regolith is a rich source of raw materials such as Oxygen Iron and Silicon. It

also contains Helium-3 which could be used in next-generation nuclear fusion powerplants on the moon, and here on Earth. Lunar regoliths consistency allows for

relatively easy strip mining, making collecting the regolith more than feasible. The

only question is how? A lunar excavator is needed to collect lunar regolith and

transport it to a processing location. In the interest of gathering new and creative

ideas to build such a device, NASA has created the Lunabotics Mining Competition.

This competition pits universities against one another in an effort to build the best

lunar excavator and test it in a simulated lunar environment. The Milwaukee School

of Engineering has had teams participate in NASA hosted completions for the past

several years, with very promising performances. These teams usually consisted of

students in their senior level design course, but this year the offer to participate in

the robotics competition has be extended to anyone with an interest in robotics

enrolled at MSOE. This years design team selected the name Manatee Mining

Systems and consists of eight Mechanical Engineering students.

Some basic specifications regarding the overall design of the robot include:

All apparatus included in the robot must be equal to or less than eighty

kilograms. (Rule #21)

Robot must be able to maneuver to the excavation zone collect the regolith

and return to the collector within 15 minutes (Rule #3, #10)

The technology incorporated into the design of the robot must be useable in a

lunar environment. No physical or fundamental processes that could not occuron the moon will be used to aid in excavating regolith. (Rule #25)

At the start of the competition attempt, the entire robot may not occupy any

location outside the footprint defined by Rule #24:

The area of a 1.5m by 0.75m square forming the cell adjacent to the

Collector.

No taller than a height of 2m.

All systems do not need to be space qualified for the lunar vacuum,

electromagnetic, and thermal environments. (Rule #26)

The robot must have a red emergency stop button of a minimum diameter of

5cm on the surface, which will kill all power and motion with 1 push. (Rule#22)

The aforementioned specification helped give way to the design which was chosen

as the starting point during ME490, shown in Figure 1.


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Figure 1: The initial robot design chosen in ME490

Manatee Mining Systems Subgroups:

The team was divided into three sub-teams.

Sensors and Controls David Swanson and Ryan Waldmann

Drive system and Excavation Zak Griffa, Mike Varga, Eugen Zinn

Structure and Hopper Rafael Arndt, Jonathan Block, and Mike Riley

The robot being built has six main elements to its design, the drive system, control

system, sensors, excavation, hopper and structure. Having worked exceptionally

the previous year, the drive system and control system will be rebuilt with the same

design. The design team however elected to redesign the other four systems.

Design for this project has been divided into three stages. The first stage was the

research and planning portion of the design process. During this stage it was

important to develop a base model of the design and determine the feasibility of

each part of the design using a qualitative perspective.. The second stage of the

design process was to take the base model from the previous part and build on it.

During this stage it was important to perform detailed design and modeling as well

as implement engineering analysis to determine whether the design could perform

quantitatively. The final stage will consist of creating the final design and vigorously

testing it before taking it to the competition.

Beyond just the design of the subsystems, there were several overall design

considerations: the stability, the weight, and the overall dimensions of the robot.


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The Design:

Sensors:

Situational awareness was a major concern for the design team this year. Learning

from last year, it was determined that there had to be a minimum amount of

measurement done. Navigation of the robot was the primary concern, leading theteam to create network camera experiments to determine lag, vibration, settling

time, and range of vision. Last year, the hoppers maximum load was exceeded,

causing the machine to break during unloading. To avoid this, Matlab coding was

written to determine if a spring/switch combination could be used for measuring the

weight of the hopper. Also, bump sensors were designed and created to test the

possibility of using switches to protect the robot from collisions. The proposed

sensor system includes 2 network cameras, one forward facing and one rear facing.

4 LED lights will be placed at the top of the structure to provide orientation from the

overhead cameras in the arena. A multi spring/switch mechanism is being built to

give the operator knowledge when specific weights have been reached in the

hopper. And lastly, bump sensors will be placed around the robot for

obstacle/collision avoidance.

Control System:

The excavator will be controlled remotely from a computer communicating via a Wi-

Fi link. Control systems will be implemented using a National Instruments sbRIO-

9623 controller board and LabVIEW Robotics software. This version of LabVEIW was

specially designed to offer programming functionality, movement subroutines, time

management, and speed control.

Drive System:

The 2010 robot drive system designed by the Lunar Baggers performed very well

during the competition, so well that The Manatee Mining Systems team has decided

to reverse engineer the track systems and modify them enough to fit the 2011

robot. The only modifications being that the gears used in the previous design are

no longer available for purchase this year.

Excavation:

Following the same route as our predecessors in 2010 and 2009, the Manatee

Mining Systems team has chosen to use a Bucket-Chain excavation system

primarily because of the simplicity and the quick excavation rate it can provide. The

design of the excavator this year consists mainly of off-the-shelf components,from MISUMI. These components were analyzed and found to be sufficient for the

loading applied to the excavator during the excavation process. Other tasks

performed by the excavation team include determining the excavation forces on the

buckets, excavator, and transmitted to the frame due to the resistance of the

material. The torque loads on the shafts and the necessary gear ratios and motor

specifications were also calculated. Finally, the excavation rate was calculated to

determine whether the excavator would be able to fulfill the minimum requirement

of at least 10kg of simulant in 15 minutes. We found that with a reduction in gear


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ratio, the excavator could fill the hopper (approximately 28kg) if necessary. A

complete model of the excavator can be seen in Figure 2, shown on page 5.

Figure 2: Complete model of the excavator.

Structure:

The primary task of the frame is to support the hopper and the excavation systems.

The frame mainly consists of inch steel tubing. The base is much like last years

design, with two small rectangular box frames resting on the drive system tracks.

The main supports of the frame connect to these using vertical and horizontal

members. The main supports will then be reinforced with gusset and diagonal

framework. The supports for the excavation system allow for manual adjustment of

the angle of attack of the excavation unit. To connect the excavation system and

the hopper to the main supports, two custom brackets were designed.

All potential high stress areas of the frame needed to be analyzed to determine any

possible modes of failure. The main supports were analyzed for buckling and


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bending. The excavation system is largely supported using two pins on either side,

which needed to be analyzed for the maximum principal stress. Other components

that needed to be analyzed for the maximum principal stress were the custom

brackets, any fasteners in the system, and the excavator braces. Additionally, all

the small components needed a fatigue life analysis. The frame was designed to

have a factor of safety of 1 in an extreme worst case scenario, and a factor of safetyof 4 in a typical loading scenario.

Hopper:

The dumping hopper mechanism will consist of a hopper with 2 sidewalls, a movable

backwall and a flapgate. Two linear actuators, two ropes, a spring and two brush

seals are also part of the dumping system. The flapgate is connected via both ropes

to the backwall which is movable. The linear actuators are attached to the sidewalls

from outside and are able to open the flapgate. So if the linear actuators start to

open the flapgate, the regolith is falling out of the hopper. After a while the backwall

starts moving too, just in case that the regolith doesnt slide itself into the collector

box. Attached to the movable backwall are on each side brush seals which have twotasks. 1st they have to seal the gap between backwall and sidewalls and 2nd they

have to make sure the smooth movement of the backwall during dumping. The

spring which is attached at the bottom of the backwall is connected also to the

frame; its task is to pull the backwall back after dumping process is completed. The

amount of regolith that can be dumped is 30.5kg with fluffy regolith: =0.75g/cm3

(73.3kg with compacted regolith: =1.8g/cm3). It has to be dumped across a wall

with the height of 1m. The hopper will have a volume of 40715cm3(41 liters) and is

separated from the excavation unit. The hopper will hang on two horizontally

beams, one on each side, which are supported by vertical beams. Switches in

connection with springs or sensors, which will be attached to the supporting beams,will be used to measure the weight of the hopper during excavation.

Final Thoughts:Additional analysis may be performed between the printing of this document and

the final presentation on Friday, February 25th; therefore all values may be subject

to change. Additionally, during the building process some unforeseen factors may

alter the final design of the system.


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Special storage instructions................................................................................96

Disposal Instructions...........................................................................................96

Timeline....................................................................................................................98

Excavator Sub-team Time Line..............................................................................98

Structure Sub-Team Timeline................................................................................99

Appendix A..............................................................................................................100

Excavator Components........................................................................................100

Appendix B..............................................................................................................115

MATLAB Code for Hopper Spring/Switch Simulation.............................................115

Appendix C..............................................................................................................116

Bill of Materials....................................................................................................116

Structure...........................................................................................................116

Appendix D..............................................................................................................120

Material Safety Data Sheets:...............................................................................120

References..............................................................................................................124

References


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Figure 41:The excavator pin support as analyzed in Ansys......................................60

Figure 42: The pin for the excavator pin support in Ansys........................................60

Figure 43: Excavator side supports as analyzed in Ansys.........................................61

Figure 44: Hopper geometry.....................................................................................62

Figure 45: center of gravity (sideview).....................................................................63

Figure 46: Rough basic 3D-model.............................................................................64Figure 47: Closed flapgate (storage position)...........................................................64

Figure 48: Start of dumping......................................................................................65

Figure 49: End of process..........................................................................................65

Figure 50: Hopper divided in sections.......................................................................66

Figure 51: Fg distribution..........................................................................................67

Figure 52: Triangle of forces.....................................................................................67

Figure 53: Supporting points.....................................................................................68

Figure 54: Cantilever theory.....................................................................................68

Figure 55: Fn distribution..........................................................................................69

Figure 56: Stress distribution....................................................................................69

Figure 57: Deflection of backwall..............................................................................70

Figure 58: Wall movement........................................................................................71

Figure 59: Angles definitions.....................................................................................71

Figure 60: Active and passive cases.........................................................................73

Figure 61: Stresses in the flapgate...........................................................................74

Figure 62: Forces acting on the flapgate...................................................................75

Figure 63: Deflection of flapgate...............................................................................75

Figure 64: Centroid of hopper backwall (side view)..................................................76

Figure 65: Distance of equilibrium point...................................................................76

Figure 66: Backwall in dumping position 1................................................................77

Figure 67: Backwall in dumping position 2................................................................77Figure 68: Backwall in dumping position 3................................................................78

Figure 69: Backwall in equilibirum point...................................................................78

Figure 70: Isosceles triangle.....................................................................................79

Figure 71: Maximum dumping position of backwall..................................................79

Figure 72: Necessary stroke......................................................................................81

Figure 73: Center Aligned Switch..............................................................................86

Figure 74: Off-center switch......................................................................................87

Figure 75: Hopper loading switch..............................................................................87

Figure 76: Wire..........................................................................................................88

Figure 77: Plate.........................................................................................................88Figure 78: Double-Switch Plate.................................................................................88

Figure 79: Spring Plate..............................................................................................88

Figure 80: Double-Switch Spring Plate......................................................................88

Figure 81: Alternative Double-Switch Spring Plate....................................................88

Figure 82: Horizontal Switch Support........................................................................89

Figure 83: Vertical Switch Support............................................................................89

Figure 84: Slotted Bracket Support...........................................................................89

Figure 85: Linksys Model WVC80N-RM Network Camera..........................................89


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Figure 86: A Limit Switch..........................................................................................89

Figure 87: LEDs.........................................................................................................89

Figure 88: Hopper Closure Switch.............................................................................90

Figure 89: Rotary Encoder.........................................................................................90

Figure 90: Excavator Bill Of Materials.....................................................................100

Figure 91: Roller bearing designs complete with mounting apparatus. The excavatorwill utilize the compact bearing design...................................................................101

Figure 92: Timing belt pulley used to transmit power between the gearbox and the

excavator drive shaft..............................................................................................101

Figure 93: Stepped drive shaft for the sprockets on both ends of the excavator....101

Figure 94: Idler sprockets used on the excavator...................................................102

Figure 95: Idler shafts used to add stability to the frame and also allow the idler

sprockets to function...............................................................................................102

Figure 96: Side Rail - Non motor.............................................................................103

Figure 97: Structural brace.....................................................................................104

Figure 98: Actuator mounting bracket....................................................................105

Figure 99: Driven shaft of the excavator assembly.................................................106

Figure 100: Excavator Bucket.................................................................................107

Figure 102: CIM Motor used in the excavator and the track systems......................108

Figure 103: P 80 gearbox used in the track system and the excavator..................109

Figure 104: P80 Gearbox.........................................................................................110

Figure 105: The engineering drawing of the lower frame.......................................116

Figure 106 The engineering drawing of the upper frame........................................117

Figure 107: The engineering drawing of the hopper support bracket.....................118

Figure 108: The engineering drawing of the excavator pin support........................118

Figure 109: The engineering drawing of the excavator side support......................119

Figure 108: The engineering drawing of the excavator side support


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Table of TablesTable 1: Elemental composition of the lunar regolith and two different lunar regolith

simulants...................................................................................................................28Table 2 Material properties.......................................................................................38

Table 3 Excavation properties...................................................................................38

Table 4: MISUMI component list for the excavator....................................................41

Table 5: Equivalent Radial Load Factors for Ball Bearings........................................46

Table 6: Dimensions and Ratings for Single Row 02-series Deep-Grove and Angular

Contact Ball Bearings................................................................................................47

Table 7: Properties of 3003 Aluminum Alloy.............................................................63

Table 8: Force acting on backwall.............................................................................66

Table 9: Force acting normal on backwall and datasheet for circle function.............68

Table 10: Stresses in backwall..................................................................................69

Table 11: Values for deflection..................................................................................70

Table 12: Deflection data..........................................................................................70

Table 13: Variables for earth pressure calculations..................................................73

Table 14: Determined values....................................................................................73

Table 15: Determined stresses.................................................................................74

Table 16: Values for deflection..................................................................................74

Table 17: Determined deflection value.....................................................................75

Table 18: Sensor Hierarchy.......................................................................................83

Table 19: Bump Sensor Alternatives.........................................................................88

Table 20: Bump Sensor Mounting Alternatives.........................................................89

Table 21: Manatee Mining Systems robot design expenses......................................92Table 22: Components included in the track assembly.............................................93

Table 23: Components include in the excavator assembly.......................................94

Table 24: Components included in the hopper assembly..........................................94

Table 25: Components included in the electrical system..........................................95

Table 26: Excavation Sub-team ME491-ME492 Timeline..........................................98

Table 27: Structure Sub-Team ME491 Timeline........................................................99

Table 28: Structure Sub-Team ME492 Timeline........................................................99

Table 29: CIM Motor specifications..........................................................................109

Table 30: Lower Structure BOM...............................................................................116

Table 31: Upper Frame BOM...................................................................................117


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Table 31: Upper Frame BOM

Project Background

Project StatementThe Manatee Mining Systems Team is designing a robot capable of competing in theLunabotics Mining Completion hosted by NASA. This completion simulates an

actual mining mission on the moon. The surface of the moon is not like the surface

of Earth. Everyone can agree that the Earth is rich with life. This fact is true for

both above and below the Earths surface. The soil composition on Earth contains a

great deal of organic material. Even the term soil infers that there is organic

material in the composition. The moon does not have life, thus the surface material

of the moon is called regolith. This regolith is rich with useful elemental

components such as Iron, Silicon and Helium-3. If these materials can be collected

from the moons surface, then they can be processed and used to manufacture

components for space shuttles and stations in space. This would essentially solvethe biggest problem facing the space program today, gravity. Almost all energy

used by space shuttles is used to escape the Earths gravity and leave Earths

atmosphere. If the shuttle could start in a low orbit the energy needs would be

greatly reduced. This means larger ships capable of taking longer trips could be

used.

On a different note, the Helium-3 is thought to be a possible solution to the energy

problems here on earth. Some scientists believe that Helium-3 which could be used

in next-generation nuclear fusion power plants, but Helium-3 is very rare on earth.

By collecting it from the moon further research could be performed.

Design SpecificationsThe robot design the Manatee Mining Systems team has chosen will meet all

competition rules and requirements to avoid disqualification. The design of the

drive train and chassis will allow the robot to move across the lunar regolith. The

material handling apparatus will contain the equipment required to excavate,

convey, and dump the collected material; attempting to reach the goal of 10 kg

(minimum) of regolith moved in the 15 minute time limit. The control of the robot

will be semi autonomous and will contain on board power for all subsystems. All

labor and materials utilized to design and construct the final design will comply with

the specifications listed below and will comply with the NASA competition rules aswe know them. They are subject to change.

The robot will compete in a 7.38m long by 3.88m wide area filled with 1m of

compacted regolith stimulant. Three obstacles with dimensions of twenty to thirty

centimeters and a mass of seven to ten kilograms will be placed inside the

competition area. There will also be two craters of varying depth and width no wider

or deeper than 30cm. The drive train of the robot must allow for avoidance or the


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displacement of the rocks by the robot in a way such that time and energy

requirements are minimized.

Overall Specifications

Based on the performance of the 2010 MSOE robotics team the following

specifications are feasible.

All apparatus included in the robot must be equal to or less than eighty

kilograms. (Rule #21)

Robot must be able to maneuver to the excavation zone collect the regolith

and return to the collector within 15 minutes (Rule #3, #10)

The technology incorporated into the design of the robot must be useable in a

lunar environment. No physical or fundamental processes that could not occur

on the moon will be used to aid in excavating regolith. (Rule #25)

The assembly and disassembly of the robot in the competition area must be

performed in less than ten minutes before the start and five minutes after the

conclusion of the completion to avoid disqualification/time penalties. (Rule#9)

At the start of the competition attempt, the entire robot may not occupy any

location outside the footprint defined by Rule #24:

The area of a 1.5m by 0.75m square forming the cell adjacent to the

Collector.

No taller than a height of 2m.

All systems do not need to be space qualified for the lunar vacuum,

electromagnetic, and thermal environments. (Rule #26)

The robot must be designed so that no part of the robot passes more than 15

cm beyond the confines of the outer wall of the Sandbox and the Collectorduring normal operation.

The robot will not be designed with the requirement of being anchored to the

regolith surface prior to the start of the competition attempt. (Rule #12)

The robot shall not be designed such that it requires to be placed on the

regolith surface with more force than its own weight. (Rule #28)

In the event that the robot excavates its way to the bottom of the Sandbox,

no part of the robot may use the bottom of the sand box for support. (Rule

#19)

The robot must have a red emergency stop button of a minimum diameter of

5cm on the surface, which will kill all power and motion with 1 push. (Rule

#22)

Drive Train and Chassis

The locomotion of the robot will be provided by a track design. The tracks

must provide sufficient traction to avoid getting stuck in the regolith

regardless of the mechanical properties of the regolith.


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Components of the robot that, during the course of normal operation, are

near material handling equipment or the drive base must be able to withstand

the impact of 10 kg stones in the event that one be accidentally excavated or

collided with.

Rotating and sliding elements, such as bearings, linear actuators, or guide

rails, must be designed such that regolith build up is prevented. Build up willcause excessive and premature wear on shafts, guide wheels, and other

precision components.

Maintenance

Worn or damaged parts should be replaced rapidly and with ease without the

need for any specialty tools.

Standard fasteners and assemblies should be utilized wherever possible, and

modular designs should be practiced where applicable.

The robot must be able to operate normaly even when it is not completely

regolith free. Components that do need to be kept regolith-free should be

designed so that removal of the regolith can be done rapidly and easily withminimal disassembly of the robotic assembly.

Materials

The materials used in the construction of the robot must be easily fabricated,

readily available, and contain properties that sustain the necessary forces

determined for the component for which it will be manufactured to produce.

Materials exposed to the regolith must resist rapid corrosion induced by the

coupling of the abrasive properties of the material and exposure to the

atmosphere and the oxidation process.

Ergonomics

The robot must be light enough that it can be lifted and placed onto and off

the Sandbox surface with relative comfort and relative ease of two to four

individuals using a team lift technique.

Critical components should be able to be accessed comfortably and with very

little physical effort.

All control apparatus required to operate the robot through teleoperation

should be located such that it is comfortable and easily to accessed by the

pilot.

FinishThe robot is representing each of the students involved, the advisor,

Milwaukee School of Engineering, and all of the sponsors and corporate contributors

of the project. Therefore, the robots final configuration will be attractive and give

the impression of a quality, well engineered product. However, the functionality of

the robot outweighs the appearance of the robot, and the visual aspects of the robot

shall not interfere with the robots operation.


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Safety

The process by which the robot navigates the Sandbox, excavates the

material, and deposits the material into the collector shall not pose a threat of

danger to person farther than 25 centimeters away from the device while in normal

operation.

Design Time

The Lunar Regolith Excavator Student Competition takes place May 25-28,

2011. A fully functioning robot will be completed by May 4th to allow two full

weeks of strategy deployment and testing of the systems integration.


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Background Research

Excavation

Rotary ExcavatorA plurality of sets of an excavating vessel and an associated soil discharging

plate are mounted on an endless rotary member in an excavator in such a manner

that said excavating vessel goes behind said associated soil discharging plate and

the free end is placed well into the excavating vessel. The free end can discharge

the soil at a predetermined position.

Figure 3: Rotary Excavator

Linear Excavator

An excavating apparatus having a prime mower with a longitudinal centerline

and a main frame with an engine, a ground drive system and an excavation boom

operatively attached thereto wherein the excavation boom has a first end and a

second end. 1st end is pivotally attached to the main frame along a main frame pivot

axis. Main frame axis is transverse to the longitudinal centerline of the prime mover.

A head shaft is attached to the 2nd of the boom. The excavation drum is mounted

onto the head shaft in a manner that the excavation drum cooperates with the

excavation chain and a fixed cutter pattern to stay in consistent alignment with thefixed cutter pattern.


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Figure 4: Linear Excavator

Bucket Conveyer

Bucket conveyor provided with a frame having upwardly inclined spaced

parallel guide rails which support the bucket for up and down movement along the

inclined guide rails.

Figure 5: Bucket Conveyor

Bucket Conveyer

Bucket conveyor comprises a drive pulley and at least one guide pulley with

endless traction cable means engaged over the guide pulley and the drive pulley. A

bucket member of a conveyor trough has an axle thereon each side and with a

pulley on the axle. In one embodiment the pulley is pivotal on the axle and in

another embodiment the pulley is fixed on the axle. In addition the construction


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includes a guide pin on the trough on each side of the axle and the endless traction

cable is trained around each guide pin and has a loop engaged over the pulley

between the pins. Construction is applicable both for a fixed bucket in respect to the

traction cable or a bucket that pivots or swings in respect thereto and in which the

bucket pulley is rotatable on its bucket axle.

Figure 6: Bucket Conveyor

Apparatus for excavating soil

An apparatus for removing soil and other debris from around buried objects.

The apparatus comprises a movable frame which supports plurality of rotatable and

independently mounted brushes which are used to gently sweep across the soil to

remove soil and other debris from the covered objects. The soil is then transferredto a collection box within the movable frame for subsequent removal. The moved

material is collected in the box right behind the brush. This principle is comparable

to that of the snow blower.


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Figure 7: Apparatus for Collecting Soil (Patent Number: US005588230)

Frames/Linkages

Construction Machine

United States Patent No. 5,006,988, Construction Machine

While this patent was not related to an autonomous machine, it provided several

key points pertinent the framework of a mobile vehicle that is subjected to loads,

such as:

The load is to be properly distributed throughout the frame

The frame is to relieve stress from other parts of the machine that may not be

as strong, such as the drive train, etc.

The frame, when loaded, behaves the same as it does when not loaded

Some interesting design concepts were also featured:

Fully rotational framework

Linkages independent from vehicle body

Frame Design

There are countless options for frame designs. This research report will only be able

to scratch the surface. The two areas of frame design that will be focused on in this

report will be overall frame styles, cross-sectional areas of support rods, andattachment methods.

Overall Frame Designs

Assuming the frame to be taller than it is wide, the frame will probably consist of

four corner posts stabilized using methods such as

Vertical beam support

Panel


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Hybrid of both (Fuselage or Space-Frame)

If the four corner post method is used then it will have to be stabilized by methods

such as

Direct beam side supports

Criss-crossing supports (on the side or top) Panels (on the side or top)

Attachment Methods

Methods to attach the perpendicular members of the frame include

Welding

Brackets with Bolts

Socket

Clamps

Snap mechanism

Cross-sectional area of supports

Many different types of cross-sectional areas could be used for the supports such as

beam

Tube

Rod

Hollow shapes

Solid shapes

Patent # 4,049,082 contains different cross-sectional area styles made from a thin

material. This patent was for strut or gusset supports, but could potentially be used

in any support rod on the excavator.


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Figure 8: Cross Sectional Area Styles

Patent #2,546187 is for a window frame, but the tube style design could be useful,

and a light weight metal mesh might be able to add some axial structural support.

Figure 9: Tubular Frame

Patent #6,604,710 is for light aircraft frame, the method for connecting

perpendicular rods might be useful.


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Figure 10: Light Frame-Perpendicular Connections

Patent #3,940,900 is a frame designed to support a panel in addition to other loads.

This might be a useful method to stabilize corner supports.

Figure 11: Frame-Panel Support


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Journal Articles

Journal article research did not return very many results for frame design ideas, but

some articles about analysis might be useful.

Approximate limit load evaluation of structural frames using linear elasticanalysis

Structural system reliability considerations with frame instability

Sensors and Electronic Devices

Some preliminary research that was done for possible sensor includes a laser range

finder, and a load cell.

Laser Range Finder

The range finder measures distance by firing a light pulse and measuring thetime it takes for the pulse to return. The optics at 13 serves to both focus anoutgoing light pulse into a beam, and to collect the scattered light of thereturning pulse.

The light beam is focused on the photon detector at 15 to measure the timedelay. Distance can be read on the digital display at 17 through the viewfinder at18

(an analog display can also be used. The system could be connected to a telescope with the optical systems would

be connected through the beam splitter, 19.

The sensor could be very useful for the project, especially if incorporated into acamera system.

Charlie W. Trussell, Jr [inventor], August 4, 1998, Laser Rangefinder, United StatesPatent

5790241


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Load Cells

A load cell generally uses a mechanical system, a strain gauge, and an electronic

amplification device. As force is applied to the mechanical system, it is thentransferred to the strain gauge. The strain can then be converted into an electrical

output and then amplified to tell how much force was originally applied.

The main location that a load cell could be used is in the measuring of the hopper.

As regolith is dumped into the container, the team needs to know when the

minimum competition requirements of weight have been met.

Shimazoe et al. [inventor], June 19 1984, Load Cell, United States Patent

4,454,771

The Lunar Regolith

How is it Formed?

The lunar regolith is formed as a result of tiny impact reactions. Microscopic

metirites impact the moons surface as such intense speeds the particles eventually

fuse together. This is why the surface material is said to behave much like glass

powder.


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Figure 12: Diagram of the formation of Lunar Regolith

Unfortunately, because of the erratic impacting of the metirites on the moons

surface, the fused regolith doesnt resemble any pattern. Each particle is unique in

shape. This irregularity is what allows the material to grab hold of anything, and

is what makes the material difficult to mine from the surface.

Health Risks

The Lunar Regolith is very fine and irregular shaped with very sharp edges. These

sharp edges allow it to stick to anything, including the inside of lungs. This also

gives the material very abrasive properties, as well as a health risk when inhaled.

Figure 13: The various shapes of lunar regolith


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Conceptual DesignsThe design concepts shown below are capable of meeting all of the design

constraints. The Manatee Mining Systems Team has chosen the 2nd concept (Figure

15) as the primary design to move forward with.

Figure 14: Concept 1 - A bucket/ brush system with wheels

Figure 15: Concept 2 - A bucket conveyor with tracks


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Figure 16: Concept 3 - A bucket wheel collector with a screw-drive mobility system

FeasibilityAll of the concepts derived from the ME490 portion of the design process have been

found to be feasible. The concerns with concept lie mainly with the mobility system.

As seen in last years competition, wheeled robots were not able to perform as

effectively as their tracked counterparts. The wheels did not have enough contact

surface area so the shear force on the surface of the regolith overcame the amount

of force required to keep the regolith together. This resulted in much sliding and a

loss of traction. The concerns with concept 3 are also with the mobility system.

Last years team performed a large amount of engineering on the track system and

in effect pioneered the technology of track systems here at MSOE. Using a screw-

drive mobility system would require a large amount of resources to design and test.

The team has decided to use its resources on other aspects of the design so the

track system from last year was reverse engineered and will be used again this

year.

By going with concept 2 the team has chosen to build a robot very similar to the

robot used in last years design. The performance of the 2010 robot in the

competition was very promising, with a few major setbacks. The team this year

hopes to tackle those setbacks and build an award winning robot.


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The ExcavatorJust as in previous years, the excavator apparatus was chosen to be bucket-chain

system. This allows for a minimum amount of components, while retaining a quick

excavation rate. By using a bucket-chain excavator the need for an additionalconveyor or digging apparatus is negated. The bucket chain excavator is capable of

digging the regolith up, and conveying it up to the hopper. Two other excavation

methods were chosen as possible alternatives; a brush collection system, and a

machine using a bucket-wheel excavator in conjunction with a conveyor belt.

The 2010 team demonstrated that a bucket conveyor could quickly fill up a hopper

as large 32kg within a few minutes, so in the interest of weight conservation the

digging width of the excavator was reduced to approximately 350mm. This

reduction in width allowed the team to exchange the reduction in width for an

increase in the overall length of the excavator.


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Figure 17: A complete model of the excavator.

Before researching in-depth what components and materials to use, it was

important to understand how the system should be modeled, and how the forces on

the components could be estimated.

Nomenclature

ah = blade acceleration in horizontal direction [m/s2]ahR = horizontal robot acceleration [m/s2]av = blade acceleration in vertical direction [m/s2]an = radial acceleration [m/s2]at = tangential acceleration [m/s2]c = soil cohesion [N/m2]d = depth of excavation [m]Fside = side friction [N]Fblade = friction on the blade [N]


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g = gravitational acceleration [m/s2]T = total excavation force [N]q = surface surcharge [N/m2]KPE = dynamic passive earth pressure coefficientK0 = earth pressure coefficient at restLW = length of failure wedge at surface [m]

PP = passive earth pressure [N]w = width of excavation blade [m]W = tool length [m]Wb = weight of excavation blade [N]Ws = weight of soil wedge [N] = inclination angle of blade []p = inclination angle of failure wedge [] = inclination angle of side friction []1 = external friction angle [] = unit weight of soil [N/m3] = friction angle between soil and blade [] = internal friction angle []

= inclination angle of acceleration [] = shear plane failure angle [] = mass density of soil [kg/m3] = tool angle []v = robot driving speed [m/s]r = radius of motion of blade [m]n = rotation speed of blade [1/min]dmax = maximal digging depth [m] = angular velocity [1/sec] = scoop angle []

IntroductionFor a scientific way of designing excavation machinery it is necessary to calculate

the resistive force of the material. To separate material, the excavation blade must

overcome the resistive force. Since the task is to excavate lunar regolith which is a

soil material the research was focused on force calculation models that are based on

soil mechanics.

Research has shown that there are different models available to calculate

excavation force but all of them were limited to specific application range and

excavation parameters. To get the most accurate result for the desired excavation

operation it was necessary to compare all of these methods and pick a model that is

most suitable for the own excavation operation.

For calculation of excavation force of the bucket chain system the Zeng Model

(Zeng, 2006) was picked since it was considered to be the most suitable Model for

the own realization of excavation.

The benefits of the Zeng Model are that it includes:

dynamic earth pressure

side friction


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surcharge

blade friction

weight of the blade

blade acceleration

The Zeng model is the only one that takes the tool acceleration under consideration.For a worst case calculation we have to consider an acceleration of the blade wile

excavating.

Figure 18 shows the excavation blade and the resulting failure wedge in front of the

blade.

Figure 18 failure wedge in soil in front of the blade(Zeng, 2006)

This model assumes that the soil in front of the excavation blade will form a triangleduring the digging process. The triangle represents the shape of failed soil wedge

depicted in Figure 18. According to this model, the excavation force T (Figure 20),

which is applied by the blade in the excavation process, is expected to face the

resistive force F (Figure 18).

This resistive force is defined by several soil parameters like the soil cohesion (c) or

the internal friction angle (), pressure of soil located within the failure wedge (), as

well as the soil above the failure wedge (q), which in means for this specific

excavation process is meant to be very small. The material dependent parameters,

for JSC-1A, have been already tested and defined by the company ORBITEC, which is

a leading subsystems integrator and high technology development company basedin Madison.

Since all excavation force calculations were developed for linear movement of the

blade it was necessary to accommodate the Zeng model to make it more suitable

for a rotational movement of the blade. Figure 19 shows the principal function

structure of the bucket chain system.


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Figure 19 excavation blade

Because of rotational movement we have a radial acceleration of the blade.

Additionally we have to consider the case of vertical acceleration of the robot during

the digging process.

Figure 20 forces act on blade (Zeng, 2006)

All calculations were done for the worst case scenario to get a higher safety factor

against failure because of a to small predicted excavation force.


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Calculation

Theory

For the horizontal robot acceleration of we assume that the excavation speed v is

reached after a specific time t.

ahR=vt (1)

Assuming a constant rotation speed for the excavation process means that

tangential acceleration of the bucket at = 0. The radial acceleration can be

calculated in the following way.

an=r2 (2)

The value of the vertical bucket acceleration is

av=ancos+atsin () (3)

The horizontal acceleration is

ah=ahR+ansin+atcos () (4)

Total bucket acceleration angle is

=tan-1ahg+av (5)

The critical failure surface is inclined from horizontal by an angle

p=--+tan-1tan-+C3EC4E (6)

Where

C3E=tan +tan++cot++1+tan--cot++ (7)

C4E=1+tan--tan++cot++ (8)

The length of the failure wedge at the surface is

Lw=dtan+1tanp (9)

The dynamic passive earth pressure coefficient is given by


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KPE=cos2++coscos2--1-sin+sin+cos--cos2

(10)

The passive earth pressure can be calculated as follows

PP=0.5KPE1+avgd2W+2cdWKPE+KPEqdW (11)

The horizontal and vertical components of the total excavation force are given by

Tx=-Fbladesin-PPcos--Fsidecos+Wbgah (12)

Ty=Fbladecos+Wb+PPsin-+Fsidesin+Wbgav (13)

Where the side friction force is

Fside=Lwcd+K0qdtan+K0tand23 (14)

Since we have a movement in x direction in addition to the rotation of the blade we

can neglect the friction force on the blade Fblade without having much influence on

the calculation. Due to the movement in x direction the blade is moving away from

the soil behind the blade. Therefore the normal stress on the surface of the blade is

expected to be small and would result in a small friction resistance.

The total excavation force is calculated by knowing the horizontal and vertical

components of it

T=Tx2+Ty2 (15)

Results

All calculations were based on data for material parameters provided by ORBITEC(,

2007) or the Lunar Sourcebook(Heiken, 1991) and represent feasible values for the

lunar soil.

Table 2 Material properties

soil density () 1800 kg/m3

soil cohesion (c) 1000 N/m2

internal friction angle () 45

soil-blade friction angle () 20

at rest earth coefficient (K0) 0.573


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Excavation parameters used for the calculations are listed in the further table.

Table 3 Excavation properties

tool angle () 60

robot velocity (v) 0.775

1

m/s

radius of motion of blade (r) 0.085 m

maximal digging depth 0.036 m

scoop angle () 0-50

width of excavation blade

(w)

0.326 m

tool length (W) 0.036 m

gravitational acceleration

(g)

9.81 m/s2

Figure 19 shows, that the inclination angle () and the digging depth (d) are both

functions of the scoop angle (). Therefore the excavation force (T) is also a function

of the scoop angle.

This plot shows that the

highest excavation force

occurs at a scoop angle of

15. The force reaches a

maximum value of 97.1N

when using material

properties from and

excavation parameters out

of table .

Figure 21 Excavation force vs. scoop angle

This plot shows the range

for an ideal tool angle ().

The lowest force occurs in a

range between 60 and 75.

The force over tool angle

was calculated for different

scoop angles to get a more

Figure 22 Excavation force vs. tool angle


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reliable result for the entire

scooping area.

This plot shows the linear

rising excavation force by

increasing the digging

depth of the excavation

blade. For the worst case

calculation the entire

bucket length was used to

get the maximal possible

resulting force.

Figure 23 Excavation force vs. digging depth

Experimental SetupAn experimental set up was developed, to prove the reliability of the analytically

calculated excavation force. The experimental measurement of the excavation force

should ensure that the accommodation of the Zeng model was made accurate

enough to provide reliable values. Figure 24 shows the 3D model for the test

apparatus.

Figure 24 Experimental Setup


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The basic idea is to measure the torque is needed to rotate the shaft and push the

bucket through the regolith. To simulate the movement of the robot in vertical

direction a linear actuator was implemented in the design of the test apparatus.

Experimental test are planned for the first week of the Spring quarter 2011.

Experimental procedure

1 As a first step it is necessary to align the lowest bucket edge with the regolith

surface and set this position as the zero.

2 A measurement of the torque in the zero position is necessary to determine

the friction torque of the system.

3 Now the bucket can be lowered by a predefined value (5mm) to initiate the

next experimental run.

4 Power the actuator measure the torque while rotating the shaft preferably at

a constant velocity.5 Plane the surface of the regolith to the zero value.

6 Repeat step 4 -5 (four times).

7 Now go back to step 3 and lower the bucket again by the predefined value

and repeat all further steps until you reach the final excavation depth of

35mm.

8 Average the values for the different digging depths.

9 Subtract the torque measured in the zero position from the averaged values.

10 Compare results to analytical calculated values for the excavation force.

Excavator components list

Nearly all of the components used in the design of the excavator were chosen from

MISUMI USA. MISUMI is an automation component supplier with custom machining

capabilities. A customer will pick one of their stock components and then specify

alterations that are desirable on the component. Even after choosing an alteration

to the component, the quoted lead time is normally less than a week. This makes

MISUMI USA a prime choice for a supplier in a project like this.

Table 4: MISUMI component list for the excavator

Component Item # MaterialSprocket BSP40B24-N-15 1045 Steel

Drive Shaft KZCE15-400-P12-LA40-LB10-KA0-HA30-KC5-HC100-KD245-HD100 1045 Steel

Driven Shaft KZCE15-370-P12-LA10-LB10-KC5-HC100-KD245-HD3 1045 Steel

Bearings SBACA6801ZZ Steel

Timing Belt TBN160XL050 Rubber

Timing Belt Pulley U-ATP32XL050-B-S0.50 2017 Aluminum

Idler Sprocket DRC40-13-12 1035 Steel

Idler Shaft AETRS12-350-SC0 2017 Aluminum


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The overall load on the mounting locations of the excavator

In order to give the structure team an idea of the load requirements on the frame, a

force balance was used to determine the forces on the mounting locations. The

initial excavation force estimate was approximately 190N in the horizontal direction

and 100N in the vertical direction. These forces were used in the calculations.

Assuming a completely static structure, the following equations were used.

M=0

Fx=0

Fy=0

The force balances can be expanded to:

M=0=Fs)x1.178m-Fs)y0.208m-FA0.56m-W(0.06m)

Fx=0=Fs)x-FA)x-FB)x

Fy=0=FA)y+FB)y+Fs)y-W

Where Fs is the excavation shear force and FA and FB are the forces on location A and

B respectively, and W is the weight of the excavator.


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The Shafts

The two main shafts of the excavator assembly are stepped 1045 Steel shafts with a

major diameter of 15mm and a minor diameter of 12mm. Both shafts were tested

using fatigue loading calculations provided by Shingley and Norton. In order to

determine the expected life of the shafts for the excavator a few assumptions had to

be made; the biggest being that the driven shaft did not experience any torsionloading.

The equation for the

Se=KaKbKcKdSe'

Sf=KaKbKcKdKeSf'

The surface factor can be found using:

Ka=aSultb

Noting that the surface of the shaft is machined, a = 4.51 and b = -0.265. Ka =

0.835.

The size factor Kb is found using:

Kb=1.24d-0.107 for (2.79d51mm)

Where d is the minor diameter of the shaft. Kb = 0.950.

From Shingley and Norton the bending load factor Kc is determined to be 1.

The temperature of the environment also plays a role in the failure of a steel shaft,

however for this case the temperature of the environment was assumed to be room

temperature or 23C. Kd=1

Another factor involved is the reliability factor. For this project an excavator

reliability of 99.9% was assumed. For this level of reliability, Ke = 0.753.

The shaft design requires that there be a step in the shaft. Because of the step

extra calculations must be performed. The stress concentration factor is found with:

Kf=1+qkt-1

Keeping in mind that the major diameter and the minor diameter are 15mm and12mm respectively and the radius of the fillet is 0.2mm, Kt can be found using

Figure 26, Figure E-2 in Shingley and Norton.


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Figure 26: Finding the stress concentration factor due to the step in the shaft

Figure 27 (Figure 6-36 in Shingely and Norton) is used to find q.

Figure 27: Notch-sensitivity factors for steels. (From Shingely and Norton)

Using the values from Figure 26 and 27, Kt = 2.9 and q 0.55, Kf = 2.045.

Plugging all of the factors in yields Se = 173.2MPa and Sf = 101.3MPa.


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The strength of endurance at 103 cycles is found using:

Sult)s 0.8(Sult)

Where Sult is the ultimate strength of the steel

Sm 0.90(Sult)s)

Using the modified endurance strength Sm, factors needed to calculate the life of the

shaft can be calculated.

b= -13logSmSe

loga=logSm- 3(b)

Both a and b are found to be 1004.06 and -0.127 respectively, and the stress in the

shaft can be found using the basic equation for bending stress in a beam:

a'=32Mad3(Kf)

Where the moment Ma is found using Figure 28 and the equation for the total

alternating moment, shown below Figure 28:

Figure 28: Moment diagram

Since the shaft is rotating, this moment is considered completely alternating. To

find the total moment, the minimum moment is subtracted from the maximum

moment and divided by two:

This yields an alternating moment of Ma = 39.78N-m.


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The alternating stress is found to be approximately 245.5 MPa.

Now the life of the shaft can be calculated using:

SN=aNb

The expected life of the driven shaft was found to be approximately 66,000rotations. With the expected velocity of the shafts being only 37rpm, the expected

life of the shaft is approximately 1800 minutes, or 120 competitions.

The Bearings

The estimated life of the bearings used in the excavator was calculated using the

loadings estimated using the Zeng model shown above. The equation for the

fatigue life of a bearing in millions of cycles is given as:

L=L10C10Pa

Where a = 3 for ball bearings and 10/3 for cylindrical and tapered bearings. The

maximum life, L10 is assumed to be 106 rotations and the equivalent force on the

bearing (P) is defined as:

P=XVFr+YFa

Where v = 1 because the inner ring of the bearing will rotate. Fr is the radial force

and Fa is the axial force. For this analysis the axial force on the bearings was

assumed to be negligible. The X and Y components are both found using Table 5

shown below.

Table 5: Equivalent Radial Load Factors for Ball Bearings

Since the axial load is zero, the value for Fa/C0 will also be zero resulting in X = 1

and Y = 0.

P=11215.325N+00= 215.325N


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C10 is a characteristic of the bearing. The bearings have a bore of 12mm and a C10of 6.89kN as shown in Table 6.

Table 6: Dimensions and Ratings for Single Row 02-series Deep-Grove and Angular ContactBall Bearings

L=106cycles6.89kN215.325N3=3.2761010cycles

Using the same velocity estimate that was used with the shafts (approximately

37rmp) yields a life of 1684.67 years. This confirms that the bearings will not fail

due to fatigue during the competition.


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The Structure

Frame

The entire frame of the robot can be distinguished as two frames, the lower frame

and the upper frame:

Figure 29: Upper and Lower Frame

Lower Frame

The lower frame is a modified version of last years lower chassis design. On the left

and right side of the lower frame are the track portions to be situated on top of the

drive tracks. Interconnecting framework and space for necessary control modules

and excavation system can be seen in the midsection between the two tracks. The

primary function for the lower frame is to provide a basis for the high stress vertical

posts partial to the upper frame, which will be welded to the lower frame. A major

modification was a length reduction in the two members that connect the track

pieces at the rear of the frame, this was done to accommodate for the narrow

excavation unit. At a maximum length of 0.7m and width of just under 1m, the lower

frame is designed to meet specifications for space and weight.

Upper

Lower


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Upper Frame

Excavator Support

The upper frame design supports the excavator directly from the base of the lower

frame with two vertical supports. Connected to the two vertical posts by pin are

members which allow the angle of the mounted excavation unit to be changed

manually.

Hopper Support

Extended vertically from the rear of the lower frame are another pair of posts

responsible for the majority of the hopper support. These posts are connected to the

vertical posts supporting the excavation unit by horizontal framework. The hopper

is supported eccentrically due to clearance needed for the linear actuators

associated with the dumping mechanism.

In its entirety, the frame is an extremely important entity to the robot because it

joins three major components together: the excavator, the hopper, and track drivesystem. Not only does the frame have to be designed to withstand the loads brought

on by these components, the frame has to remain stable while these components

are performing their necessary functions, simultaneously.

Engineering Analysis

Weld Analysis

Despite a few pins and fasteners, welding is going to be the primary joining process

for the members in the frame. It therefore becomes very important, from an

engineering design standpoint, to determine the best and strongest welds to use, aswell as what type of loads may cause the welds to fail.

Assumptions

The welds that join the members of the lower frame can be neglected for

analysis, or assumed strong enough for their intended function.

Attention will be focused on the high stress welds: Where the vertical posts

meet the lower frame

Analysis

The vertical posts are considered the high stress members because the front posts

take much of the load from the excavator and the rear posts take much of the load

from the hopper. These loads are dissipated along the member though various

fasteners and finally the weld, where it is transferred elsewhere to the lower frame.

Figure 30 provides a visual representation of these weld locations.


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Figure 30: Rear Support Welds and Front Support Welds

For these vertical posts, the main objective for the analysis was to determine if this

type of weld, a parallel fillet weld, is feasible for the loads considered, or if an

alternative type of weld, such as a perpendicular weld or modified T joint weld

(where the end of the vertical post is welded to the top of the lower frame at oneinstance, instead of the side at several instances) is a better choice.

To simplify analysis, each vertical hopper support was subjected to a compressive

load equal to half of the maximum load seen if the hopper were to be completely full

of regolith.

F=392.2N

19.4mm

3.175mm

Figure 31: Parallel Fillet Weld Diagram

Weld analysis for the front vertical posts was approached the same way as the rear

posts. Assuming that each post was to take half of the maximum compressive loadgenerated by the excavator, the maximum shear stress at the minimum throat area

would be:

=1.414Fhl=1.414*161.45 N3.175 x 10-3 m(19.4 x 10-3m*4)=926.6 kPa

Observing the shear stress at the throat area is beneficial because if failure of the

weld were to occur due to compression, this is where it would occur. Based off of the

shear stress calculations, which were calculated using maximums loads at worst

3.175

For a parallel fillet weld, the maximum shear force on the

minimum throat area of the weld can be determined by

the following equation:

=1.414Fhl=1.414*392.2 N3.175 x 10-3 m(19.4 x 10-

3m*8)=1.125 MPa

For the rear hopper support seen in Figure 30, the

vertical post is actually joined to two sides of the lower

frame instead of one, increasing the amount of welded

areas to 8 instead of 4, hence the factor of 8 used in the

equation above.


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case scenarios, the stresses are still well below tolerances of the weld, concluding

that the parallel fillet weld would be a suitable choice.

Another welding option for the vertical post would follow in the form of a T joint

weld, which can be seen in Figure 32:

Figure 32: T-Joint Weld1

T-joints are actually more commonly seen when two large plates are being joinedtogether. If this method were to be implemented instead of the parallel fillet, one

would be welding together two pieces of equal cross-sectional area, which would

make for a more difficult weld. Grooves are often beveled in T-joints for improved

stability, a task that requires additional machining and skill. This weld would also be

more susceptible to bending moments due to the cantilever-like orientation that the

weld creates.

In summary, the parallel fillet weld is the better choice because:

It allows more surface area of the joining members to be welded, resulting in

a smaller shear force

Does not require additional machining

Less likely to fail from bending and torsion

Hopper Support Posts Analysis

Figure 33 shows the typical loading scenario of the hopper. The left side of the figure

shows how both posts support the hopper and the right side shows how the load

from the hopper is seen by one individual post. As can be seen from the diagram,

both the weight (W) and the distance (D) between the support posts and the

centroid of the hopper are reduced.

1 Edgar, Julian. "AutoSpeed - Beginners' Guide to Welding, Part 1." AutoSpeed - Technology, Efficiency,Performance. Web. 19 Feb. 2011.

.


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Figure 35: The top view of the hopper given full capacity

[ ] [ ]

2 2

2 2

2 4

(784.3 )(5.73 ) (784.3 )(26.8 6.54 ) 13.34784.3

0.8716 0.8739

377.3

1.35

y xxy

cr xy

cr

cr

Worst Case

M M cM cP P

A I A I

N cm N cm cm cmN

cm cm

MPa

FoS

+= = + = +

+ += +

==

[ ] [ ]

2 2

2 2

2 4

(784.3 )(5.73 ) (784.3 )(13.4 6.54 ) 13.34784.3

0.8716 0.8739

114.3

4.44

y xxy

cr xy

cr

cr

Typical Case

M M cM cP P

A I A I

N cm N cm cm cmN

cm cm

MPa

FoS

+= = + = +

+ += +

=

=


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Buckling

Both ends of the hopper support post will be welded to cross members, thus in terms of column

analysis the posts can be considered fixed-fixed with an effective length half that of its actual

length (see Figure 36).

Figure 36: Fixed-Fixed ends in terms of column analysis

According to the Manual of Steel Construction, there are two different modes of

buckling failure. The first happens in the intermediate range and the second

happens in the slender range. The maximum length given the previously

calculated bending stresses is desirable, thus the first calculation will be in theslender range.

4

2

2 2 2

2 2

0.8739.11.01

0.8716

21.92/ 2

1.921.92

cr cr

creff cr

I cmr cm

A cm

E E EL r

L L

rr

= = =

= = =


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2 2

2 2

(200 )2 2(1.01 ) 52.2

1.92 1.92(377.3 )

(200 )2 2(1.01 ) 94.8

1.92 1.92(114.3 )

cr

cr

cr

cr

Worst Case

E GPaL r cm cm

MPa

Typical Case

E GPaL r cm cm

MPa

= = =

= = =

The worst case stress gives a maximum length of 52.2 cm, but the longest unsupported section

will be 49cm. The second portion of the buckling calculations will determine the factor of safety

in terms of stress. However, it must be first determined if the 49cm section is in the slender or

intermediate range.

( )

2 2

4924.3

2 2 1.01

2 2 (200 )88.2

508

eff cr

y

L L cm

r r cm

E GPaCc

MPa

= = =

= = =

Since Cc is greater than L/r, the member is in the intermediate range. The factor of safety can be

found using the following formula.

3

3

5 3 / 1 /

3 8 8

5 3 24.3 1 24.3

3 8 88.2 8 88.2

1.77

L r L r FS

Cc Cc

FS

FS

= +

= +

=

Excavator Support Posts

Figure 37 shows the excavator and one of its support posts. In the figure the excavator is digging

and at full capacity. Aside from the drive motor, the rest of the excavator is assumed to be an

evenly distributed load.


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Figure 37: Side view of the excavator and its support post at full capacity:

To solve for the unknown reactions the sum of the forces and the moments was determined. Since

all of the forces are pivoting around the middle support pin, R2x is assumed to be 0.

1

1 3

3

3

0

97.3 0

0

29.4 252.1 0

0

0.478 (sin12 )29.4 0.359 (sin12 )100.6 0.172 (sin12 )48.1

0.516 (sin12 )48.1 0.873 (sin12 )51.8 1.058 (cos12 )97.3

0.688 (cos12 )

158.3

x

x

x x

y

y

Ro o o

o o o

o

x

x

F

R R N

F

N N R

M

m N m N m N

m N m N m N

m R

R N

=

+ =

=

+ =

=

+ +

+ =

1 61xR N =


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Due to excavator centroids location in the z-axis in Figure 5x, additional moments on the

components supporting the excavator are:

On the lower support:

( )97.3 0.159 15.5yyM N m N = =

On the middle support:

252.1 (0.159 ) 40.1xxM N m Nm= =

Assuming a worst case scenario where all the forces are supported by the

middle pin, the forces on the pin will be as follows:

29.4 (0.17 ) 252.1 (0.24 ) 65.5

97.3 (0.24 ) 23.4

29.4 (0.72 )sin(12 ) 252.1 (0.11 )sin(12 ) 10.1

252.1 29.4 281.5

97.3

o o

Moment xx

N m N m Nm

Moment yy

N m Nm

Moment zz

N m N m Nm

Force y

N N N

Force x

N

= =

+ =

=

Using this worst case scenario, the excavator beam was analyzed in Ansys. The length of the

beam used was the actual length of the beam between the middle pin support and the fixed lower

support on the lower frame.


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Figure 38: The excavator beam analyzed in Ansys

Based on the Ansys analysis and an elastic strength of 508Mpa for the steel tubing, the factor of

safety for the excavator support beam is 1.98.

Bracket Analysis

Hopper Support Bracket

The hopper bracket was designed to transfer the load on a horizontal beam to a vertical beam

given a 20 cm offset. The bracket was analyzed in Ansys given the worst case loading for the

hopper that was previously calculated.


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Figure 39: The hopper support bracket

Figure 40: The hopper support bracket as analyzed in Ansys

Based on the Ansys analysis and an elastic strength of 270Mpa for aluminum, the factor of safety

for the hopper support bracket is 4.6.


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Excavator Pin and Pin Support

The excavator pin and pin support assembly is designed to allow the excavator system to pivot

when manually adjusted for a different angle of attack. The assembly will be primarily taskedwith supporting the direct weight of the excavator and the moment that it induces in the zz-axis as

in Figure 10x.

Given loading conditions if the middle support for the excavator was the only support, the

excavator pin support and its pin were analyzed in Ansys.

Figure 41:The excavator pin support as analyzed in Ansys


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Figure 42: The pin for the excavator pin support in Ansys

Based on the Ansys analysis and an elastic strength of 270Mpa for aluminum, the factor of safety

for the excavator pin support is 7.8. Based on the Ansys analysis and an elastic strength of

508Mpa for shaft steel, the factor of safety for the excavator pin support is 1.6.

Excavator Side Supports

The excavator side supports are primarily tasked with supporting any induced moments and

horizontal forces in the excavator system.

Given the typical loading conditions of 158.3 N in the horizontal direction and a moment of

15.5Nm acting around the yy-axis, the excavator side supports were analyzed in Ansys. In Figure

43 the far right hole was considered a fixed support and the far right hole was where the force and

moment were applied.


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Center of gravity:

It is also important to know the center of gravity, because it influences the interface

between the supporting beams and the hopper. The center of gravity is shown in

xxx and can be calculated like the following:()

s=423r=423300mm=180.06mm

xs=scos=180.06mmcos45=170.32mm

ys=ssin=180.06mmsin (45)=170.32mm

Material selection:

The material that will be used for the hopper, has to be chosen very carefully, due to

the restriction of 80kg for the entire excavator. Therefore the excavator has to be

very light, but it has also to resist the force of the regolith which acts on the hopper.

The worst case would be a fully loaded hopper where the regolith is compacted

(=1.8g/cm3) and with the volume of 40.7 liter, the mass will be 73.3kg which would

create a force of almost 719 N.

To accomplish all of these tasks improved-strength basic aluminum (alloy 3003) will

be used.

This is a general purpose manganese alloy that is the most widely used of all

aluminum alloys. The addition of Manganese increases the strength by 20% over the

1100 (pure aluminum) grade. This combines the excellent characteristics of 1100

with higher strength. It has excellent corrosion resistance. It is not heat treatable

and develops strengthening from cold working only. The AL 3003 alloy is readily

machined and is considered as having good machinability for the aluminum alloys. It

has excellent workability and it may be deep drawn or spun. It can be welded by allconventional processes. This alloy is commonly used to make cooking utensils,

pressure vessels, builders hardware, decorative trim, mail boxes, awnings, siding,

storage tanks, window frames lithography plates and storage tanks. ()

The stresses, forces and deflections which act on the hopper walls will be calculated

later on.

Table 7: Properties of 3003 Aluminum Alloy

Form Sheet

Condition H12 at25C

Density 2730 kg/m3

Poissons Ratio 0.33

Elastic

Modulus70-80 GPa

Tensile

Strength130 MPa

Figure 45: center of

gravity (sideview)


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Yield Strength 125 MPa

Elongation 10 %

Hardness 35HB50

0

Shear Strength 83 MPa

FatigueStrength

55 MPa

Concept:

Figure 46: Rough basic 3D-model

The Hopper consists basically of 2 sidewalls, a backwall, a flapgate, 2 linearactuators and 2 ropes.

The flapgate is connected via both ropes to the backwall which is movable. The

linear actuators are attached to the sidewalls from outside and are able to open the

flapgate. So if the linear actuators start to open the flapgate, the regolith is falling

out of the hopper. After a while the backwall starts moving too, just in case if the

regolith doesnt slide itself into the collector box. The sidewalls will hang on 2

supporting beams. The idea is to measure the weight of the hopper during

excavating with switches or sensors which are attached to these supporting beams.

Hatch seals at the edges of the backwall will close the gaps between the backwall

and the sidewalls. This ensures that the regolith isnt able to flow through the gaps.

Although these hatch seals create friction, it has to be determined experimentally if

this concept works, or if other devices have to be considered. The following pictures

show steps while dumping the regolith.


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Figure 47: Closed flapgate (storage position)

Figure 48: Start of dumping

movable

regoli

fla

rop


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7497,1

2

4288352,

64

75,7237

3

150

6813,6

45

3897404,

94

68,8203

8

180

5913,6

45

3382604,

94

59,7300

4

210

4661,5

05

2666380,

86

47,0829

5

240

1961,5

05

1121980,

86

19,8119

4

270

0 0 0 300

Total 69851,7

39955172,4

705,5284

Table 8: Force acting on backwall

Figure 50: Hopper divided in sections

Figure 51: Fg distribution


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Figure 52: Triangle of forces

Figure 53: Supporting points

Figure 54: Cantilever theory

By the means of the circular function the slope was determined, so that it was

possible to get FN.

fx=r-r2-x2=300-3002-x2

f'x=m=x3002-x2


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FN [N] Distance

[mm]

[degrees

]

m

[slope] y x

90.67552 0 0 0 0 0

89.30733 30 5.73917

0.1005

04

1.5037688

68 30

86.11583 60 11.537

0.2041

24

6.0612308

66 60

81.09954 90 17.4576

0.3144

85

13.818239

57 90

74.2557 120 23.5782

0.4364

36

25.045458

3 120

65.57867 150 30

0.5773

5

40.192378

86 150

55.0563 180 36.8699 0.75 60 180

42.65578 210 44.427

0.9801

96

85.757147

14 210

28.24977 240 53.1301

1.3333

33 120 240

8.635824 270 64.1581

2.0647

42

169.23303

17 270

0 300 180 8 300 300

FNtotal=70

5.52

Table 9: Force acting normal on backwall and datasheet for circle function

Figure 55: Fn distribution

Figure 56: Stress distribution

A [mm2] FN Distance


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[mm] [N/mm2]

17168,0

4 90.67552

0

0,005282

17193,1

5 89.30733

30

0,005221

17238,6

9 86.11583

60

0,005099

17311,5

6 81.09954

90

0,004911

17425,3

5 74.2557

120

0,00465

17608,5

3 65.57867

150

0,0043

17930,5

9 55.0563

180

0,003838

18622,6

4 42.65578

210

0,003207

23190,0

9 28.24977

240

0,00203

20563,8

4 8.635824

270

0,0009630 0 300 0

Table 10: Stresses in backwall

r= 300 mm

h= 3 mm

b= 570 mm

F=621.6302

742 N

q0

=

1.319140

412 N/mm

l=

471.2388

98 mm

E= 70000 N/mm2

Iy

= 1282.5 mm4

Table 11: Values for deflection

Iy=bh312

l=2r4

q0=Fl

wx=q0l4360EIy3xl-10x3l3+7x5l5

fm=q0l4153.3EIy in x=0.519l

Maximum deflection: fm=4.7267mm


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Documents

ME_Manatee Mining Systems_Design Report REV17