Design of Lunar Backhoe.pdf

8/10/2019 Design of Lunar Backhoe.pdf

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FINAL REPORT

ME 4182 DESI6N

Design of a Lunar Backhoe

Submitted to _r. Brazell

June 3_ 1985

Submitted by:

Brian Hatchell

Jeff KruegerScott LandersSteve DollRob SchenkRick Wilkins

( Team 2 )

(NASA-CR-Id2847) dESIGN OF A LUNAR _ACKriO_

Final Report (Georgia Inst. of Tech.)

129 p

00/37

N90-/1224

w_


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ABSTRACT

This report examines the the design of a backhoe to be used

on the moon's surface. Several modifications had to be made tothe existing conventional backhoe to. make the backhoe suitable

for the lunar environment. Among the problems encounteredinclude dissipating heat, controlling the backhoe in a soundlessvaccuum_ and accounting for the difference between the earth's

and the moon's gravitational fields. This group was left free todetermine its own design parameters for backhoe performance.


3/81

PROBLEMSTATEMENT

Backqround

NASA is currently looking into the feasibility of buildinga lunar base station. Out of necessity_ there is now arequirement that specialized earth moving equipment be designed.This equipment must be able to work in the lunar environment aswell as have the capacity to perform its function on the lunarsoil. This particular team has been designated to design a lunar

backhoe. The design will incorporate some of the basic kinematicand fundamental principles of an analogous earth backhoe.Ho_ver_ there will be modifications to the controlling

(maneuvering) system and power system of the backhoe. This teamhas been left free to set its own design and performancespecifications.

Performance

The backhoe must be able to interface with the given

tractor design. This interface _ill consist of 5_th a physicalcoupling and, in this case_ a hydraulic coupling. The hydrauliclines will be shielded to prevent high heat buildup due to theconstant solar radiation. As a further precaution_ the hydraulicfluid will have a flash point in excess of 400 degrees F ( 205

degrees C). The backhoe will exert high digging forces, which,along with the weight of the backhoe_ will have to be

counterbalanced by the weight of the tractor and outriggers onthe backhoe. This digging forcer as yet unspecified, will be inthe range of 1000 Ibs. as a result of the combined cylinderforces in excess of 9000 lbs. The capacity of the bucket will be

in the range of 7 cu. ft. and the maximum digging depth will bein the range of 120 in. (304.8 cm). The bucket may be equippedwith quick disconnects to allow for the easy installation of

other buckets_ other tools_ etc. The different links will bedesigned to be lightweight_ have low heat capacity, and havehigh strength to prevent bending. This criterion will give rise

to a tube design. The backhoe will also have to be a free

standing unit when not in use.Environmental limitations will necessitate designing aremote control package for the backhoe. These controls may have

a resistant feed back loop so that the operator can feel thebackhoe working_ or a relief valve may be placed in the

hydraulic system. Both of these precautions will prevent theoperator from overloading the system.

Constraints

The main constraint of the backhoe is the lunar

environment. Basically, it is in a vacuum, constantly night orday, with a constant influx of solar radiation and one sixth the


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gravity of earth. This poses several problems for the backhoe.There will be a large heat buildup in any mass put there and theonly means of heat transfer will be by radiation. Thus_ it willbe difficult to dissiPate heat due to friction or heat buildupin the hydraulic lines. Since there is only one sixth thegravity as that on earth, it will be difficult to counterbalancethe digging forces. Due to the vacuum_ it will be necessary forthe operator to wear a spacesuit and this will limit theoperator's maneuverability and his field o vision. The vacuumwill also make it impossible to hear the equipment operating.

The lunar soil is also a limiting factor. The soil is a

cohesionless_ fragmental rock type. It will be very abrasive tothe materials and will necessitate the use of very hard

materials. It is also a powdery top soil which will furtherlimit the operators _ield o_ vision.


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CONTROLS

The open loop control system used to control the backhoe

cylinders consists of a stack of six electro-machanical

servo--valves, a handheld controller/transmitter, and a radiorecei vet.

The valves are four-position, two way, closed centerdirectional servo-valves that uses a torque motor to control a

spool that diverts the hydraulic fluid into and out of thecylinders. The position of the spool is proportional to the

magnitude of current to the motor. The amount of flow of thehydraulic fluid is controlled by the position of the spool. Atthe null position, no flow passes to the cylinders, and at fullrated current to the motor, full rated flow is driven to the

cylinders. Six valves are used to control the backhoe: one eachfor the shovel, bucket, dipstick, swing, and left and right

outrigger cylinders. One valve is used to control the two swingcylinders.

The valves that were selected are stackable, with one

connection needed for inlet pressure and one for oulet. Full

pressure ( 2500 psi ) is available to each cyclinder. To preventthe operator from overloading the system, relief valves arelocated at the inlet manifold and at each valve stage. Each ofthese relief valves are to be set at 2500 psi. To limit the

maxium force exerted by the cylinders, pressure control valves

are to be placed between the valves and the cyclinders.The maximum temperature under which the valves can be

operated is 100 degrees Celsius using Viton seals. With the

hydraulic fluid heat exchanger, the valves should be suitablefor operating for an indefinite period. Other specificinformation for the valves is located in the appendix.

The valves are controlled by a radio receiving unit that

drives the torque motor with a current proportional to thestrength of the input radio signal. The input signal ismultiplexed to allow for maximum signal reliability. Otherfeatures of the receiver include: environmentally sealed NEMA-4

Junction Box_ internal mountings that permit the unit to bedirectly mounted to the backhoe, a plug in card that mates thereceiver to one sending unit so that several backhoes may be

operated in one area, and ramp output for the proportional

controls for smooth cylinder motion. The receiver requires a 12volt power source, so that the box can be directly connected to

the tractor's battery.The receiver should be mounted on the tractor where it will

not be physically abused and where it can provide clear line ofsight to the operator location. It is suggested that thereceiver be mounted at the rear of tractor near the backhoe

interface. The receiver can be operated at or below 140 degreesFarenheit. Given that the reciever will be stored at 70 degreesFarenheit and that the maximum temperature of the backhoe will

be 250 degrees Farenheit, a properly shielded and insulatedreceiving box could be operated for at least 4 hours under

direct radiation. Material suggested for shielding andinsulating the receiver are the same as those used to protect


6/81

the hydraulic lines.The controlling/transmitting device is a portable handheld

sending unit with 6 spring loaded levers for proportionalcontrol and 8 spring loaded toggle switches for on/off control.Only the proportional controls will be used to control thebackhoe. The sending unit can either be clipped to the spacesuit of the operator or hung around his neck with a neck strap.The controls can be operated with the operator wearing gloves.The sending unit uses a 12-volt rechargeable battery thatprovides 4 hours of continous operation. Other features of thesending unit include: environmentally sealed UHF transmitter_custom label for controls, 2 dead man switches (one of whickmust be depressed to operate the sending unit), and 1/4 mile

line of sight control.A suggested configuration for the control on the sending

unit is provided in Figure I . With the controls set up as

shown, the operator can use the backhoe for digging by squeezing

the dipstick and boom levers together with his left hand. Also,to dump a load of soil, the swing and bucket levers can be

squeezed together with the right hand. This configuration willprovide maximum convenience for the operator, and was suggested

by an actual backhoe operator.The sending unit converts data from the on/off switches and

potentiometers into digitally coded l s and O's. Five bitsprovide for thirty-two possible levels of control where fifteenare for + and -- control each and the remaining t_o levels

provide for control off . Scanning of the switch andpotentiometer positions occurs at a rate of twenty times persecond. ]lle transmitter is capable of providing four different

FM frequencies.The receiver operates at the same frequencies as the

transmitter. An included scanner samples the carrier frequency

continuously for a .15 second period. When data is received itis sent to a shift register where it is compared to a codecard to check for agreement between the code card and sending

code. When the comparisons are checked and confirmed, the datais transferred from the shift register to the a position in

memory. The data is then processed through buffers and relaysfor the on/off switches and digital/analog converters for the

proportional controls. The next digital data is similarlyscanned and if the comparisons are successful, the data enters

memory one twentieth of a second later. Included in the receiverare several fail-safe logics. The sending code must be verified

for each data set, several successive ON commands must be

processed to turn the function on, and valid transmissionoutput will return to zero within one-half of a second ifsucceeding command data is not received.

The control system for the lunar backhoe was designed to beeasy and safe to use, easy to set up and service, and withfeatures to prevent the operator from damaging the system. Radiocontrol was selected over manual control to give the operator

manueverability to compensate for his inherent difficulties with

seeing out of a space suit. Moog was chosen as a vendor for the

radio controls because they were the only company that provideda radio transmitter and receiver that could be used directly


7/81

Figure $

Suggested Control Arrangement for Radio Sending Unit

Left

Swing B

Ri ght

Out

Bu kt El.In

Down

Left Outrigger E

up

hbuttont

Moog

SendingUnit

Out

Dipstick

In

Up

Boom

Down

Down

_ Right Outrigger

Up

i i


8/81

with servo-valves without additional electronic hardware. Theircontroller is by no means the most convenient one that could be

designed for the backhoe operator: a two joystick tummy packwould provide for a system closer to the one on conventional

backhoes. The joysticks would also be easier to use with gloves

on the operator's hands. But designing such a unique system

would introduce complexities that woud require matching manyelectrical components compatible with the chosen servo-valves.The sender/receiver from Moog was specifically designed to becompatible and electrically matched for the servo-valves. Sowith this system, we have a tried and proven system with nocom40atibility problem.

The chosen valves are stackable into a very tightconfiguration for easy mounting on the backhoe. With the relief

valves on the main manifold and for the individual cylinders,the operator or the load cannot easily overload the hydraulic

system. Also, with the pressure controlling valves between thecylinders and the valves, the maximum force exerted by thecylinders can be limited. This will prevent the operator fromlifting the tractor off the ground.

The specification sheets that were provide by Moog for thevalves, transmitter, and receiver are provided in the appendix.


9/81

HYDR_I_LIC SYSTEM - GENERAL SPECIFICATIONS

The hydraulic system is designed to operate using GeneralElectric Versilube F-50 hydraBllc fluid over a temperature rangeOF to 2OOF. Hydraulic hoses and cylinders which can operateeasily under these conditions have been selected and are speclf_ed

in their respective sections. In addition, provision has beenmade for a liquid convection cooling system and shielding againstsolar radiation so that the considerable amount of heat generated

under operating conditions can be dissipated.A_I cylinders are double acting and honed for concentricity

and finish. The piston rods are hlgh-tensile, die drawn steel,

hardened, ground, polished, and chrome plated. Cylinder pistonpackings are of the chevron type. The rod packings are of thechevron type also, but incorporate a viton U seal. The

packing gland supports and retains the rod packing, bearing sleeve,rod wiper, and backup ring. Cylinder pivot and anchor pointsutilize self lubricating bushings. The swing cylinders employ

a connecting hose at the rod ends of the cylinders that permitoil flow between them.

The main control valve is a stack-type assembly consistingof six sections containing spring centered, remote controlledspools which direct high pressure pump oil to the individualcylinder circuits. Each circuit contains a spring loaded check

valve to check the flow from either cylinder port to the valvepressure passage. Also, each section contains adjustable circuit

relief valves to protect against pressure overloading. The maincontrol valve is also equipped with an inlet end cover and an

outlet end cover. The inlet end cover contains the inlet portand the system relief valve. The outlet end cover contains the

return oil port which returns low pressure oil to the reservoir,and the backpressure relief valve. The backpressure relief valveis a simple pilot operated relief valve that functions when the

pressure in the return oil passage is approximately 250 psi great-er than the pressure in the sump oli passage.


10/81

HYDRAULIC FLUID COOLING

Method One

Since the ambient temperature on the moon is high and

the enviornment is a vacuum it is necessary to cool the hy-

draulic fluid. The friction of the fluid will produce much

heat and since there is no air, the heat cannot be transferred

to it. The radiation will be blocked by the shield; however,

the shield will in turn radiate heat to the hydraulic line.

The simplist solution to this problem is to enclose the

whole hydraulic line with a fluid. This fluid will be contained

in the outer hose of a coaxial hose scheme where there are two

hoses, an inner and an outer. The sections of line that are

rigid tubing will then be rigid coaxial tubing.

Th_s coaxial tubing is common and can be purchased from

System Components in Atlanta, Georgia. There seems to be no

manufacturers of coaxial hose and coaxial hose fittings. The

hose can be assembled with the recommended teflon hose inside

a common two inch stainless steel hose. The fittings can be

machined and assembled (see later drawings).


11/81

Backhoe Design

All the materials used in the backhoe are made of an

aluminum alloy 60&&-T&. This alloy contains the strength_workability_ and machinability necessary for the tubular design.

The boom member is of a C-section design to provide space forthe radiator used to cool the hydraulic system. The dipperstickmember is a tubular section since the hydraulic components arenot internal to that member. All members have been designed as aconstant strength beam. This criterion is defined such that thesectional modulus is equal to or greater than the maximumbending moment at a section divided by the maximum allowable

stress in a member. The shape of each member follows the shapeof the bending moment curve closely_ thus defining the taperedsection toward the pin ends. All members are a constant 1/4 inch

in thickness. The bucket to be used will be a standard steel_ 18inch bucket whose capacity is 4 cubic feet (heap capacity wouldbe approximately & cubic feet).The backhoe will be made with a

quick disconnect at the bucket interface thus allowing for adifferent bucket or a different tool to be used. The guide linkand bucket link will also be of aluminum. All pins to be

incorporated in the backhoe will be of a carbon steel alloy. Ateach pin connection there will be a pressed fit sleeve that willabsorb the forces and distribute them evenly to the aluminum. In

this way_ stress concentrations will be greatly reduced in thevicinity of the pin connections.

The hitch_ which is the physical coupling to the tractor_consists of two parts: the pivot hitch and the interfacinghitch. The pivot hitch will be of cast aluminum 6066-T&. This is

where the backhoe connects indirectly to the tractor. Thefunction of this hitch is to produce the swing angle of the

boom. It contains the bore hole about which this hitch pivotsand it also contains the single pin connection to which theswing cylinders connect. The interfacing hitch_ as the namesuggests_ is the direct connection to the tractor. The interface

consists of a hooked bottom and a pin connection at the top;this will allow for easy disconnection and connection. The hitchconsists of a four inch tube stock frame with four 1 1/2 inch

aluminum plates welded and supported to the frame. The swingcylinders are connected in the center of the two sets of plates.

The stabilizer cylinders and legs are also an integral part ofthis interfacing hitch. The connection between the pivot hitchand the interfacing hitch will be time consuming and

complicated. First the pivot hitch is press fitted with a sleeveand inserted between the aluminum plates on the interfacinghitch. Once the bore holes line up_ the sleeve is then linebored and the resulting bore hole is fitted with a pin.

We are assuming that the bearing surfaces used are of a

non-lubricating type. This will eliminate the need for any hightemperature grease or self lubricating bearings.


12/81

Hydraulic Cylinder Specific Vendor Information

Carter Controls, Inc. will custom build h_draulic cylinders tothe dimensions listed for their Roundlin_welded cylinders.These cylinders are capable of extended operation at 450 degreesF and 3000 psi. The required structural specifications weredeveloped in the section on cylinder sizing. Mounting conditionsare shown in the main diagram of the hydraulic system.

Bucket Cylinder Special Requirements

1) Pivot Mount Both Ends, Use Eye RE 2.2) Equip Cylinder with external tubing such that both

connections are at cap end- use 3/4 ' steel tubing with 1 1/16 -12 SAE 37 degree Flared male fittings, facing cap end.

Dipstick Cylinder Special Requirements

1) Pivot Mount Both Ends, Use Rod Eye RE 3.2) Equip Cylinder with external tubing such that both

connections are at center and facing cap end- use 3/4 steeltubing, same fittings as bucket cylinder.

Boom Cylinder Special Requirements

1) Pivot Mount Rod End, Use Rod Eye RE 3. CLevis mount Cap End-RC 3.

2) Equip Cylinder with external tubing subject to sameconditions as Dipstick Cylinder.

Swinq Cylinders (2)

1) Pivot Mount Cap End of both, rod end of one; use CLevis;mount RC3, rod end of other use Rod Eye RE 3.2) No external tubing.

Stabilizer Cylinders (2)

1) Pivot Mount Both Ends, Use Rod Eye RE 3.2) Equip Cylinder with external tubing such that bothconnections are at cap end_ one cylinder with connections atright angle on left, the other cylinder with connections at

right angle on right. Use 3/4 steel tubing_ same fittings asbucket cylinder.


13/81

PIN CONNECTIONS

All the pin connections will be similar. The description

of one will be demonstrational for the rest. The main problem

is that there needs to be a high strength steel pin connecting

the rod eye of the cylinder to the aluminum member. The alum-

inum member welded up as shown in the drawings, is much softer

than the pin and upon any impact, the aluminum will absorb

the energy since there is going to be some clearance between

them. The solution is to insert an alloy steel sleeve inside

the aluminum member by means of a press fit. Thus the sleeve

will absorb some of the impact energy while redistributing

the remaining energy over a large area of aluminum.

The aluminum member shown in the drawing will be welded

as shown and then line bored to exact tolerances. The pin and

steel inserts will be machined 4340 steel drawn at lO00OF having

a hardness of 50 to _5 Rockwell C scale. The machining

operation will use a cubic Boron nitride tool which is capable

of machine this very hard steel.

The pin will be held in place by the plate coupler on the

end. Grade eight bolts will extend through this coupler plate

deep into tapped holes in the aluminum member.

Bearings that will be used in the pin connections will be

a low speed, non-lubricating bushing type. The bearings are

called _etcar tm high temperature bearings and are capable of a

working temperature of 750F and a maximum temperature of 900OF.

They can be purchased from Metalized Carbon Corporation located

in ossining, New York.


14/81

MATERIALS

In the area of structural materials, there is a need to

minimize weight and maximize strength and toughness. It was

found that high strength aluminum would be the most suitable.

Although some high strength steel alloys have a higher strength _

per pound, the aluminum was found to be more favorable. Three

aluminum alloys were under consideration. First, 7050 T736

has twice the fatigue strength of the others and is commonly

used for die forgings in aircraft; however, it is difficult

to weld. Secondly, 6066 T651 has a UTS of 57000 PSI and is

commonly used as forgings and extrusions for welded structures.

It is difficult to weld with gas but can be welded by arc.

Thirdly, 6061 T6 has a UTS of 42000 PSI and is commonly used

in fabrication because of its ease of fabrication. It has ex-

cellent welding characteristics both for gas and arc.

The GXXX series aluminum alloy contains silicon and mag-

nesium while the 7XXX contains 1% to _ zinc with smaller per-

cents of magnexlum, copper and chromium. The 7XXX series has

by far the best strength characteristics; however, due to its

poor welding characteristics the 6066 T651 and 6061 T6 are the

alloys that are recommended.


15/81

COST ANALYSIS

Description Vendor Part# Quantity Price

Note: all hose is Deutsch Co. Teflon High Pressure with TeflonCore and Steel Braid Cover.

16 Flexible Hose 207220241612

244028

36

5440 ....3624

408032

3/4 Steel Tubing.` 48 .Standard.` Use 1 1/1612 Thread Female

SAE 37deg _ I aredconnections, both ends

Bucket CylinderDipstick CylinderBoom CylinderSwing Cylinder

Stabilizer Cylinder

84A0100012C01684A0100012C02084A0100012C07284A0100012C02084A0100012C024

84A0100012C01684A0100012C01284A0100012C02484A0100012C040

84A0100012C02884A0100012C036

84A0100012C05484A0100012C040

84AO100012CO3&84A0100012C02484A0100012C04084A0100012C080

84A0100012C032

1 $8.00

1 $10.006 $216.001 $10.001 $12.00

1 $8.001 $6.002 $24.00

1 $20.0O1 $14.002 $36.00

1 $27.001 $20.002 $36.002 $24.00

1 $20.002 $80.00

2 $32. OO

2 $20.001 $300.001 $450.00

1 $700.002 $300.002 $4OO.O0

Aluminum Tubing 6066 T6

Manufacturing o_ Materials10 men

12 weeks40 hrs/week

$18/hrPins and SleevesSleeve Insert

Bearings.` high temperature

Metallized Corp.Ossing.` NY

Additional Labor

Hydraulic Lines_ etc.10 men

8 weeks

40 hrs/week3200 hrs

185/hr

900 ibs $2700.00

4800 man/hrs $86400.0021 $882.OO21 $441.0021 $756.00

3200 man/hrs $57600.00


16/81

Coaxial Hose 350Bucket, StandardRod EyesShielding

feet

controlsNote: all parts are provided by Moog Corp.

Proportional Electrohydraulic Directionalvalves for dipstick, boom

and swing cylinders A65-20-3-W-L-250valve for the bucket

cylinder Ab5-20-3-W-L-250

Inlet Manifold AssemblyOutlet ManifoldSending UnitProportional Plus

On/Off ControllerTranmitterBattery PackJunction Box

A31094-2-250A31102-1V

130-180125-104128-103

Prototype ProductionTesting

2500 man hrsRemodification

121

Control Valves

3

I

113

1

$1750.00

$480.O0$210.00$1000.00

$75O.0O

$25O.OO

$100.00

$101.00

$100.00

$I00.00

$200.00$200.00$200.00

$45000.00


17/81

HAZZARDS

The biggest foreseeable hazzard is the hydraulic fluid.

The one specified is able to withstand extremely high tem-

peratures. The high temperatures combined with its high

pressure, could cause extreme harm to someone if there was

a failure in the hydraulic line.

Another hazzard might be in the area of materials. Six

thousand and seven thousand series aluminum anneal at 775OF

in about three hours. The beginning annealing temperature

would be less than that. It is clear that the temperature

of the aluminum, when setting in direct sunlight should not

exceed a temperature limit well below this 775OF. If the

material were allowed to anneal, it would loose its heat

treated strength and this might fail under load.

Physical hazzards to the operator do not exist since he

is removed from the backhoe.


18/81

FORESEEABLE DESIGN PROBLEMS

The main area of failure would have been in the area of

hydraulic line heat transfer; however, this problem has al-

ready been solved by methods previously discussed. The method

used to cool the fluid as it returns to the tractor has not

been considered since it is not our responsibility.

The power source that drives the hydraulic pump was never

specified. We simply assumed that it existed and were not con-

cerned with the problems that would arise because of it.

The bellypack controls will be very awkward to the operator

since the operator will be somewhat removed from the work area

and will not have a good view. He will not be able to tell

how deep the hole is nor the angle that the bucket is cutting.

We have not made any provision for the mobility of the

tractor. When the trench is dug in the area that is specified,

the tractor will need to move forward to dig the next portion.

It will be almost impossible for the operator, which is removed

from the tractor, to get it in the correct location, assuming

that there are the appropriate controls added to his bellypack.

The only foreseeable solution is to install a computer

guidance system that would have the trench coordinates already

preprogramed in it. Then when the trench has been dug up to

the base of the tractor, the computer would then advance it

ten feet so that the trench could continued to be dug.


19/81

If a computer were to be incorporated into the backhoe

system, it should include the actual backhoe operation. It

would be ideal to be able to specify the depth of cut and

cordinates of the trench and let the computer do the rest.

A backhoe like this, compared to the one we have designed

is like comparing complexity to simplicity.

In my opinion, the backhoe designed with controls con-

tained on a bellypackis not feasibla, and the computerized

backhoe is the only way to solve the problem of the operator

being removed from the machine.

D


20/81

CONCLUSIONS

The lunar environment introduces numerous obstacles to be

considered when designing a backhoe or the moon. The lack of

air, heat dissipation_ soil mechanics, and gravitational fieldall add to the complexity of creating a machine that willefficiently dig foundation trenches for a lunar base.

Heat dissipation appears to cause the greatestdifficulties. Not only does the heat fail to convect in thelunar environment_ but the electronic equipment is not designedto withstand temperatures encountered on the moon. The limited

time for the electrical component's usage could be overcome byfurther detailed design in the electronic components used.

Continuous operation of a hydraulic system in such anenvironment is indeed possible using commercially availablecomponents as long as a heat sink is available. The most

important considerations are preventing heat entry by radiationand providing an adequate amount of surface area for heat

dissipation to the cooling fluid. These areas are critical sincethe backhoe is a dynamic implement and must be designed suchthat there is a minimum of bulk and weight. We are sure thatfurther_ more detailed analysis of the problems will yield

designs that are much more efficient and effective_ yet we feelthat our design is a credible first approximation.

The control system that was designed is simple in form. The

components used were chosen for compatibility and for simplicityof the overall system. While closed loop feedback using loadsensing transducers was not used, the open loop system we chose

is a workable one_ with many measures to insure that the systemwould not be overloaded by the operator. The backhoe can besafely controlled by an operator in a space suit_ but noteasily. The sending unit chosen has rather small turn controls

making it difficult to operate two controls at once with one

hand. Certain measures were taken to overcome this problem, andthe unit has been used to control a three degree-of-freedom

forklift, but the operator will probably find operating thebackhoe a little tedious.

The mechanical layout of the backhoe is a design that willachieve the project objectives. The C-section of the boom was

neccesary to provide space for the radiators in the hydraulic

circuit. Such a section will require that the boom be internallybraced to prevent floppyness.


21/81

Recommendations

It is recommended that an alternative to a backhoe beconsidered for the earth-moving requirements_ such as using a"Ditch Witch". The "Ditch Witch" potentially has severaladvantages over the backhoe: its rate of soil removal is greaterthan that of the backhoe, it can collect loose dust as itremoves the soil to prevent a visibility problem for theoperator, and it can be programmed to dig a ditch without anoperator being present. Other specific recommendations for eachsection of the backhoe follow below.

Hydraulic System

Since each side of the piston displaces a different amountof fluid _ the flow rate of fluid to one side of the cylinderand out of the other is not the same. To balance the flow rate

between sides of the cylinders, it is recommended thatcounter-balanced flow rate control valves be used in the

hydraulic circuit. Also_ it is suggested that the design of a

pneumatic backhoe be considered. Since air has no flash point_ apneumatic system would ease the maximum temperature constraintof the working fluid in the circuit.

Controls

It is recommended that the controller be redisigned toinclude two joysticks to allow for easier two--hand operation.Load sensing feedback control could be incorporated into the

control system to provide for better system protection. Also_ acomputer could be used to control the backhoe in certain

standard operations_ such as in digging a ditch.

Mechanical Desiqn

It is recommended that an existing design be used for thedimensions of the boom, bucket, and dipstick. With such a

design_ the kinematic calculations have been carried out_ andthe design has already been optimized. With backhoes of manydifferent specifications curently available_ one should be able

to choose a design that would meet specific needs. Given such adesign_ more effort could be concentrated into the areas of heattransfer and material selection.


22/81

_ C/linJer t_ore. Do/_s_(_e.. ric.fion ,*_sar_. o-=I,-_.(G_)T_, e. =-[O_of_ tl_,,o_, _,,',;,-,-:-.,_,,


23/81

HYORAULIE OY1r, DE 5PEC F CP.-rlONS

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24/81

3T_ DIPSTICK CVLINDE_.

;r, , For_e _ _'000 lto

[_ Rod Di_,_te_ j No=3 _=2P_R= 3 F..., =/% _ootb

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ALTERNATE DESIGNS

Although the backhoe is functionable, it is very inefficient.

The purpose of it was rather ambiguous; however, now to our under-

standing, it is to dig the footings of a building to be used as

a lunar base. If this assumption is correct, a backhoe is the

wrong machine to use. It is unnecessarily large, heavy, and

clumsy. It is capable of digging holes ten feet deep which

are not needed. It has a hard time digging a trench with a

constant depth due to the controls. If the purpose of the

machine is to dig trenches then the machine to be used is a

trencher, since it would be simpler to make and also to operate.

It would be composed of two rotating wheels each with

teeth about them. The two wheels would be rotating in opposite

directions thus almost eliminating the horizontal digging forces.

The only force of significance would be the vertical force push-

ing down and would be limited by the machine_ weight. This

force could easily be increased by accumulating the soil being

dug into a large container until the desired vertical digging

force is reached.

The machine would not have wheels but rather bulldozer

type tracks to assure good traction.

This machine would be much easier to be computer controlled

compared to the backhoe since it has such a simple design com-

paritively.

The first drawing shows the two rotars having their height

controlled by hydraulic cylinders. For regular trenching, the

depth of the first rotar (dl) is half of that of the second(dE).

2d I = _


42/81

Weekly Progress Reports

Design Section: Rob SchenkRick Wilkins

Week Proqress

2

3

4

5

Picked team members

Picked study topic- soil mechanicsPicked design topic-- BackhoeGroup meeting

Divided up study topic into sub-topics: books_ technicalreports_ abstacts_ govt. documents.Group meeting

Organized material for progress meeting.Progress Meeting

Suggeted a photocopy list of all material for centralinformation file.

Group meeting

topic is finished- have lists typed upGroup meetingGathering of all typed material for fianl listing in

information file

progress meetingturned in soil mechanics material

started backhoe designBrazell gave us a starting pointSplit up into groups- controls

hydraulicsdesign

Vendor informations obtained- Vermeer

meeting with Jeff Kreugerdiscussed kinematic problems and design ideas

group meeting- Rob Schenck- more info on catepillarSteve-check out lunar atmosphereScott and Brian- controlsRick- lunar soil

continued with kinematic initial designProgress meetingdiscussed syllabus for remainder of quarteravailability of IBM- 3erry Insilia

Word Processing for writing reportProblem statement due 5/2

Group meetingDiscussed hydraulic line problems and design

Posed problem statement for review_discussion_ revision_ etc.

Determined capacity and digging depth

final form of statement to be typed up Wednesday-BrianRob-talk to Catapillar representative-get details on

interface for hitch_ hitch design initiated.Controls info received


43/81

&

7

8

9

Progress meetingTurned in problem statement, revised digging forces.Concentrated on hydraulic lines_ shielding temperature

limits, etc.Discussed purpose of VSMF catalogConsult this for Vendor informationcontrols group interface with hydraulics.Group meetingMore vendor info- FordDesign is complete, meet with Brazell to determine

member sections.More work on controls and valves for hydraulic system.Consult VSMF standards to determine position for digging

forces.Progress meetingearly meeting with _r. BrazellMethod for determining section modulus in backhoe

sections.

Quick disconnect idea is discussed.Control problem discussed- flow rates proportional toforces which in turn determines cylinder sizes.

Looked at buckling problems.Materials for suitable use is suggested: low emmissivity.

low reflectivityStill need final details on hitch.

Stabilizers and swing ranges and sizes.

Choose digging forces to initiate sizing of system.Materials chosen. Aluminum 6066 T-&

Modified hitch to incorporate labor intensive work.

Progress meeting.Initial hitch design complete- modify for swing cylinders

Dig Forces- take individual cases to determine reactionforces, don_t add

interface-- choose design.design complete, finish sections

Initial design has to be changed- bending momentsdidn't work out in boom member.

Final changes made in hitch

final drawings competed.Backhoe final drawings done.Force analysis complete.

Choose section modulus to incorporate cylinders andheat exchanger.

Change from original tube section to C-section.


44/81

Weekly Progress Reports

Controls Section: Brian HatchellScott Landers

Week Proaresq

1

2

3

4

5

6

7

?

Had organizational meeting to determine individual dutiesfor research assignment: Hatchell, technical reports

Lenders, government reportsSearched microfiche, journals, and government reportsrelevant to soil mechanics.

Continued searching library material for soil mechanicsliterature relevant to project. Wrote down findings tobe compiled into class data base.

Researched TomCat for vendors involved in remote control,

radio control, and electro-mechanical hydraulic valves.Considered alternative designs to relieve the operator'sinherent vision problem. Decided that radio control wasthe safest solution to the problem.Worked on problem statement, and researched Tomcat foradditional vendors that might be needed.Wrote letters to 15 prospective venders and called 3others in the areas of hydraulic valves and radiocontrol.

Wrote up problem statement, typing.Called up Moog for servo valves.

Researched library for textbooks that could help insetting up the control system. Selected 5 books thatwere moderately helpful. Read these books and learnedabout the specific kinds of valves that would be needed

to complete the system. Learned about overall hydraulicsystem.

Group meeting.Looked over the vendor information that we received

and determined that we probably had information on allthe components that we wouZd nemd_ except for a radioreceiver and a transmitter. Called up the Moogrepresentative for the Atlanta area and he said thatMoog had a radio receiver and transmitter that wouldprovide the proportional control of servo-valves that

we would require. He agreed to send us the informationthat we would need to set the system up.

Given the hydraulic information from Rick and Steve,we were able to determine the valves that would be

required. Luckily, we had a stackable control valvethat could be easily set up on the backhoe. The sizesand accessories that would be needed were determined.Considered cross-port verus regular relief valves anddecided that the regular relief valve was the best forour application.

Went out to the Ford tractor place and looked at a


45/81

backhoe similar to the backhoe that we were dssigning.Because the Moog representative failed to mail us theinformation that we asked or_ we drove out to hisoffice. We talked with him for about 45 minutes about the

system that we Nere designing. He suggested severalalternatives including position and load feedback

control. These measures would require additionalelectronic hardwarep and we decided that using reliefvalves and pressure controlling valves would be asimpler, but still adequate solution.Completed the overall design of the control system.

Worked on typing up the report.


46/81

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Documents

Design of Lunar Backhoe.pdf