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2016
Design of a Small
Scale Dynamometer
MECHANICAL ENGINEERING CAPSTONE 2016
KYLE TRUBE
ANDREW POWERS
NICHOLAS DIFABIO
DAVID ANDREWS
August 10, 2016
Anthony Duva
Associate Professor
Wentworth Institute of Technology
Dear Professor Duva,
Enclosed is the final report for Group 5’s RC Dynamometer project. This report contains
an overview of the project from start to finish.
At this point, the design, manufacturing, and testing phases of the project have been
completed. A working prototype of the dynamometer has been built and the results of
testing show that the design meets specification.
The final report contains detailed breakdowns of the project specifications, plans,
background research, results, and recommendations for future work. Please review the
information and feel free to contact us with any questions.
We look forward to hearing from you.
Sincerely,
Kyle Trube
Nicholas DiFabio
Andrew Powers
David Andrews
i
Abstract Dynamometers are used far and wide for automotive testing and evaluation. Currently
there exists only a few dynamometers which are commercially available and suited for
small‐scale radio controlled models. The aim of this project was to develop a
dynamometer – a system for measuring torque, force, and power – for use with RC cars.
To accomplish this, the basic principles of a dynamometer were adapted for use in a
small‐scale environment. This project includes the design of mechanical structures,
power transmission, electronic, and instrumentation systems. A prototype dynamometer
has been built and tested. The deliverables for this project include overviews, detailed
information, a poster presentation, and a working prototype.
ii
Table of Contents Abstract ........................................................................................................................................... i
Problem Definition ........................................................................................................................ 1
Background Research ................................................................................................................. 2
Project Objective.......................................................................................................................... 3
Mechanical System: ................................................................................................................. 3
Electrical System/Instrumentation: ......................................................................................... 3
PC Interface: ............................................................................................................................. 3
Calibration/Testing: .................................................................................................................. 3
Project Plan ................................................................................................................................... 4
Team Members and Qualifications ........................................................................................ 4
Relevant Coursework:........................................................................................................... 4
Relevant Course Projects: .................................................................................................... 4
Relevant Personal/Group Projects: ..................................................................................... 4
Support Personnel and Equipment ........................................................................................ 4
Facilities and Equipment .......................................................................................................... 4
Gantt Chart ............................................................................................................................... 5
Project Plan Review ...................................................................................................................... 6
Labor Statistics ............................................................................................................................... 6
Budget ............................................................................................................................................ 7
Actual Expenditures ..................................................................................................................... 7
Grading Criteria ............................................................................................................................ 9
Results ........................................................................................................................................... 10
Design Overview ..................................................................................................................... 10
Drivetrain Assembly ............................................................................................................. 11
Frame Assembly .................................................................................................................. 16
Load Absorption Design ........................................................................................................ 18
Clamping Method .............................................................................................................. 20
Shaft Brake Loading FEA .................................................................................................... 21
CFD analysis ......................................................................................................................... 22
Shaft Brake CFD ................................................................................................................... 22
Friction Material ................................................................................................................... 23
Bill of Materials ......................................................................................................................... 24
iii
Drawings ................................................................................................................................... 27
Instrumentation ....................................................................................................................... 45
Calculations ............................................................................................................................. 48
Instrumentation Setup Procedure......................................................................................... 50
Calibration Procedure ........................................................................................................... 50
Testing Procedure ................................................................................................................... 51
Results ....................................................................................................................................... 52
Discussion of Results ................................................................................................................ 56
Conclusion ................................................................................................................................... 57
Recommendations ................................................................................................................. 57
References .................................................................................................................................. 58
Appendix ...................................................................................................................................... lix
Appendix A: Test 1 Results ...................................................................................................... lix
Appendix B: Team Contract ................................................................................................. lxiii
Appendix C: Team Member Resumes ................................................................................ lxiv
Appendix D: Purchase Orders ............................................................................................. lxviii
Appendix E: LabVIEW Block Diagrams.............................................................................. lxxvii
List of Figures
Figure 1: Example of available RC Dyno ................................................................................... 1
Figure 2: Gantt Chart ................................................................................................................... 5
Figure 3: Rendering of Dynamometer Design ........................................................................ 10
Figure 4: Roller System Assembly .............................................................................................. 11
Figure 5: von Mises Plot of Roller Assembly ............................................................................. 12
Figure 6: Maximum von Mises of Shaft ..................................................................................... 12
Figure 7: Deformation of Roller System with Predicted Torque ............................................ 13
Figure 8: Maximum von Mises Stress with Measured Torque ................................................ 13
Figure 9: Maximum Deformation with Measured Torque...................................................... 14
Figure 10: First Mode Shape of Roller Assembly...................................................................... 15
Figure 11: Shaft FEA Free Body Diagram ................................................................................. 16
Figure 12: Frame Assembly ........................................................................................................ 16
Figure 13: Front Mounting Method ........................................................................................... 17
Figure 14: Rear Mounting Method ........................................................................................... 18
Figure 15: Shaft Brake Mounted (highlighted) ........................................................................ 18
Figure 16: Free Body Diagram of Shaft Brake-Load Sensor Interface ................................. 19
Figure 17: Spring Selection......................................................................................................... 19
Figure 18: Fabrication Process .................................................................................................. 20
iv
Figure 19: Brake Clamping Method ......................................................................................... 20
Figure 20: Brake Lever Diagram ................................................................................................ 20
Figure 21: Shaft Brake von Mises and Displacement Plots .................................................... 21
Figure 22: Iso-Clip of 1st Principal Stress. Areas in Tension ..................................................... 21
Figure 23: Contact Pressures on Shaft ..................................................................................... 22
Figure 24: Shaft Brake Load Magnitude Scaling .................................................................... 22
Figure 25: Air Temperature and Shaft Surface Heat Flux ...................................................... 22
Figure 26: Shaft Brake Surface Temperature .......................................................................... 22
Figure 27: Part #10001 - 8020 Extrusion 15" .............................................................................. 27
Figure 28: Part #10002 - 8020 Extrusion 21" .............................................................................. 28
Figure 29: Part #10003 - 8020 Extrusion 4" ................................................................................ 29
Figure 30: Part #10004 - RPM Bracket ...................................................................................... 30
Figure 31: Part #10005 - 1/2" Dia Alum. Shaft .......................................................................... 31
Figure 32: Part #10006 - 5" Dia X 3" Lng Roller ......................................................................... 32
Figure 33: Part #10007 - Shaft Brake Bottom ........................................................................... 33
Figure 34: Part #10008 - Shaft Brake Top ................................................................................. 34
Figure 35: Part #10009 - Friction Material Insert ...................................................................... 35
Figure 36: Part #10010 - Top Plate ............................................................................................ 36
Figure 37: Part #10011 - Load Sensor Bracket ......................................................................... 37
Figure 38: Part #10012 - Fan Bracket........................................................................................ 38
Figure 39: Part #10013 - Roller Flange ...................................................................................... 39
Figure 40: Assembly #60001 - Frame Assm. ............................................................................. 40
Figure 41: Assembly #60002 - Roller Shaft Assm. .................................................................... 41
Figure 42: Assembly #60002 - Roller Shaft Assm. Exploded View ......................................... 42
Figure 43: Assembly #60007 - Shaft Brake Assm. .................................................................... 43
Figure 44: Assembly #60010 - Fan Mount Assm. ..................................................................... 44
Figure 45: DAQ System Diagram .............................................................................................. 45
Figure 46: TAL220 Load Cell ....................................................................................................... 45
Figure 47: TAL220 load sensor (highlighted) ............................................................................ 46
Figure 48: Assortment of Hall Effect Sensors ............................................................................ 46
Figure 49: Screenshot of LabVIEW VI........................................................................................ 47
Figure 50: Instrumentation Wiring ............................................................................................. 47
Figure 51: Test 1 Results .............................................................................................................. 52
Figure 52: Test 2 Results .............................................................................................................. 53
Figure 53: Test 3 Results .............................................................................................................. 54
Figure 54: Test 4 Results .............................................................................................................. 55
Figure 55: Typical DC Motor Plot............................................................................................... 56
List of Tables
Table 1: Projected Budget........................................................................................................... 7
Table 2: Actual Expenditures ...................................................................................................... 7
v
Table 3: Resonant Frequencies of Roller Assembly ................................................................ 14
Table 4: Bill of Materials .............................................................................................................. 24
Table 5: Basic RC Car Calculations .......................................................................................... 48
Table 6: Moment Arm Force ..................................................................................................... 49
Table 7: Prony Brake Calculations ............................................................................................ 49
1
Problem Definition Currently on the market, there are few companies that sell RC dynamometers. Of these
companies, most do not provide all of the parts needed or computer interface is not
provided, and some even market systems as a “Dyno” which only measure RPM. There
is a need for an RC dynamometer that is "turn-key," fully assembled and ready to run,
which is simple enough for the average hobbyist to use. By providing a simple and
effective RC dyno, hobbyists may optimize the performance of their RC cars. By using
the system, a hobbyist can gain performance data at any point in the car's RPM range,
analyze this data to understand where optimization is needed, tune their vehicle, and
test again. Repeating this cycle until the RC car performs at its peak is critical; an RC
hobbyist will appreciate the capabilities of this system because it will help them
understand their car and will help them win whatever competition they are in.
Figure 1: Example of available RC Dyno
The need of better selection for the hobbyist community can be realized by some of
the current RC dyno providers. McPappy Racing of Las Vegas, NV builds a high quality
Engine and Chassis Dyno [3]. The problem is that the dyno comes as a kit, which needs
to be assembled, and the hobbyist needs to buy additional parts after buying this kit in
order to start testing their car. What if some of these components do not work or the
hobbyist does not assemble it correctly? Having a complete and ready-to-run
dynamometer allows the hobbyist to quickly test their vehicle, all while having peace of
mind that the system will work reliably. Also, companies like Speed Passion and Parma
were providers of RC dynamometers but have ceased selling them. Overall, selection is
limited and an innovative "turn-key" RC dynamometer is needed in the hobbyist
community.
2
Background Research A Dynamometer is defined as a system utilized to measure the force, torque, or power
of a machine. In racing industry several types of dyno are used as a test bed for
quantifying the effect of modifications on a vehicle. The first dynamometer to be
applied to an internal combustion engine was the “Prony Brake”, used to test tractor
engines around 1910. The first vehicle dynamometer came in 1928 [6]. Currently, many
types of dynos are employed in vehicle and power plant development.
There are many types of dynamometers differentiated by mounting style and brake
type. Dynos classified by mounting type are engine, chassis, and hub dyno. Common
brake types used are Eddy Current, Generator, Hydraulic Brake, Inertia, and Water
Brake. Depending on the load type, a Dyno may be able to run a wide open throttle
test and a steady state test. Wide open throttle tests simply obtain a torque and
horsepower curve throughout an engines RPM range. An operator sets the vehicle in
one gear, opens the throttle first very slightly, then to 100% immediately [6]. The vehicle
accelerates the roller as quickly as it can, while a data acquisition system records the
load cell reading or flywheel speed and time. Inertia brakes measure the time it takes
for a vehicle to spin a heavy flywheel to max speed, then calculate the torque. An
Inertia Dyno can only perform wide open throttle testing. In other load types, torque
from the engine is applied through the brake to a moment arm mounted with a strain
gauge. The strain reading on the moment arm is used to directly determine the load
being applied to the moment arm, and therefore the output power of the engine. A
high precision steady state dyno would be able to read the pulse of torque from and
multi-cylinder engine.
A key aspect of Dynamometers is accuracy and precision. Accuracy is the ability to
measure close to the actual value, precision is the ability produce repeatable results
regardless of actual value. If a dyno is being used to measure the power curve of an
engine before and after the addition of power-modifying parts, precision is more crucial
than accuracy. If an engineering department needs an exact torque output of an
engine, accuracy is more important.
Dynamometers have applications in vehicle development, racing vehicle
development, and engine tuning. There are dynamometer units for motorcycles, cars,
tractors, trains, standalone engines, etc. One of the areas where Dynos make only a
sparse appearance is in the world of RC vehicles.
3
Project Objective The objective of this project is to build a two-wheel drive mechanical braking
dynamometer that measures chassis horsepower, with data output to a PC interface, of
a Traxxas Stampede or equivalent RC vehicle and is easy for the average hobbyist to
use.
In order to meet this objective, the mechanical, electrical, and data logging systems
have to be built and work simultaneously.
The following needs will be satisfied while keeping simplicity and manufacturing in mind.
Mechanical System: The main frame to hold the RC car, other mechanical equipment, and electrical
equipment. Particular attention to adjustability of mounting components to the
main frame and also strapping the RC car down is needed.
The drivetrain to transmit power from the wheels of the RC car to the braking
mechanism. This includes the rollers at the RC's wheels and gearing to the
braking mechanism.
The braking mechanism to apply an opposing load to rotation of the RC car
wheels. This will incorporate the usage of a force sensor on a moment arm
connected to the brake that measures the force that the RC car generates to
overcome that braking force.
Heat transfer analysis of braking mechanism. Much heat will be generated and
needs to be cooled in order for the braking system to continue to work properly.
Electrical System/Instrumentation: A force sensor on the braking mechanism. This will ultimately relay force readings
to the PC and be converted to torque.
An RPM sensor to work simultaneously with real-time force readings. This will
ultimately help create power and torque plots as a function of RPM.
A DAQ/Arduino system to relay sensor readings to the PC interface. This is the
mechanism that talks to the PC.
PC Interface: LabVIEW or equivalent PC interface that displays data from the RC dyno. This
includes force and RPM readings, torque value display, and power and torque
plots based on different loadings of braking mechanism.
Calibration/Testing: Ensure sensors are accurate. Method depends on each type of sensor.
Ensure that the RC dynamometer actually functions. This includes mechanical
systems, electrical systems, and PC Interface.
Test all systems with different braking loads.
Find trends in data acquired from testing.
4
Project Plan
Team Members and Qualifications The group members for this project are Nicholas DiFabio, Kyle Trube, Andrew Powers,
and David Andrews. All four team members have a demonstrated record of academic
and industry success. All members have over a 3.5 GPA and are majoring in
Mechanical Engineering. Industry experience ranges from robotics to medical to
defense, providing a diverse knowledge base. Three members are minoring in
manufacturing which will provide expertise with manufacturing process. CV’s for each
group member are contained in the appendix.
Relevant Coursework:
Mechanical Design and Analysis
Design of Machine Elements
Engineering Dynamics
Computer Aided Manufacturing
Manufacturing Processes
Mechanics of Materials
Circuit Theory and Application
Mechanical Engineering Design
Engineering Heat Transfer
Simulation Based Design
Instrumentation and Design of Experiments
Relevant Course Projects:
Prime Mover Simulation and Motor Redesign
Gearbox Design
Engine Hoist Redesign
Relevant Personal/Group Projects:
GMC Truck Restoration
Mini Baja Off-road Vehicle
Kayak Building
Arduino Programming
Support Personnel and Equipment The project is primarily supported by Professor Duva, who acts as an advisor to the
group. Laboratory technicians provide support during lab work.
Facilities and Equipment The project will require the use of the Kingman Projects lab for fabrication of
components.
5
Gantt Chart
Figure 2: Gantt Chart
6
Project Plan Review According to the project plan, this project was completed on time. Calibration and
testing, the last step of the project, was completed before it was due. It was found that
the mechanical design and electrical design took a week longer than expected. It was
also found that the mechanical build and electrical builds took longer than expected.
Designing did not cover some obstacles that were discovered while building the
dynamometer so that is why these steps took about 2 weeks longer than expected. On
the other hand, calibration and testing took much less time than expected. It only took
approximately 1.5 weeks to gain accurate data from the dynamometer.
Labor Statistics - 531.75 hours total (not including last full week of classes)
-Assuming a pay rate of $35.00 an hour for an entry level engineer, this would equal
approximately $19,000 in labor cost.
-Assuming a standard work week of 40 hours, this project could be designed and
manufactured in 3.3 weeks.
-Prototype cost is $19,500
-Assuming a shipment of 100 units for the first year and a manufacturing time of 20 hours
per unit, selling price to break even would have to be $1,402.
7
Budget The following table 1 shows the projected budget for the project.
Table 1: Projected Budget
Actual Expenditures Table 2: Actual Expenditures
Order Date Description Order total
6/15/2016 Load cell and amp $ 21.50
6/15/2016 Bearings from SDPI $ 66.04
6/15/2016 McMaster Order $ 287.89
6/27/2016 Jumper wires for Load Cell $ 4.29
7/1/2016 McMaster Order (friction mat, thread cutting screws) $ 54.74
7/8/2016 Shaft collar and Thrust Bearings $ 20.31
7/8/2016 6061 stock for: brake, sensor mount. (donated) $ -
7/11/2016 Shaft Brake Spring $ 20.22
7/14/2016 Cigarette Lighter Adapter $ 4.98
7/20/2016 Cooling Fan $ 12.35
7/20/2016 Acrylic top $ 20.00
TOTAL $ 512.32
*Note: For full purchase orders and receipts, please see appendix
8
As you can see by comparing table 1 and table 2, the actual amount spent on the
project was $87.68 less than the projected budget. The projected budget was $600 and
only $512.32 was spent, this was 85.3% of the budget. Some general guidelines to help
reduce cost:
Avoid placing multiple orders with the same supplier in order to reduce shipping
costs.
Look for other suppliers. Most of the orders for this project came from McMaster-
Carr
9
Grading Criteria There will be an RC Dynamometer, physical system and DAQ system that reports chassis
power output. Grading will be based on the effectiveness of the physical system,
electrical system, PC interface, and operation of the complete unit.
Effectiveness: whether or not each system aids in meeting the project objective of the
RC dynamometer.
10
Results
Design Overview
Figure 3: Rendering of Dynamometer Design
According to the specifications of this project, the RC Dyno needs to be a 2wd system
that reads power output as a function of RPM. Physical, electrical, and PC interface
systems need to be created in order to obtain the project specifications. This final
design reads power transmitted from the wheels of the car to a load cell that is
connected to a braking mechanism. The operation of the dyno is as follows:
The mechanical system consists of the Stampede RC car mounted on an 80/20
aluminum frame, which was chosen for adjustability purposes. The drivetrain includes
plastic rollers that the RC car’s wheels mount on, a shaft that connects the rollers
together, thrust bearings for lateral stability, and high speed needle bearings that hold
the shaft on the frame. Connected to the end of the shaft, outside the frame, is the
shaft braking mechanism that has an adjustable clamping force via hand brake clamp.
The shaft brake design includes a moment arm that comes into contact with a load cell
which in turn reads the load transmitted.
11
Drivetrain Assembly
Figure 4: Roller System Assembly
The drivetrain assembly of the dynamometer (shown in fig. 4) consists of two HDPE
rollers, two shaft flanges, one 7075-T6 aluminum shaft, two thrust bearings, two shaft
collars, and two needle bearings. The drivetrain assembly allows for the power of the
rear wheels of the RC car to be transmitted to the rollers and onto the shaft. The power
transmission will allow for the measurement of rpm from the rollers and torque from the
shaft brake mechanism. The shaft brake mechanism will be mounted directly on the
shaft.
A ½” diameter 7075-T6 aluminum shaft (McMaster Carr Part #9063K16) was chosen to
mount the rollers due to its rigidity, resistance to torsion, and it met the need for
tolerance requirements (0.5000” +0.0000”/-0.0005”). The needle bearings require high
tolerance so it was cost and time effective to buy this part instead of machining a
custom shaft. Another benefit of using aluminum is for heat dissipation around the shaft
brake. Due to the nature of the shaft brake, a high amount of heat would be
generated due to friction and therefore it is imperative that a material with a high
thermal conductivity is used to allow for more efficient cooling.
Upon static and vibration analysis, it was found that the shaft exceeded the
performance requirements necessary for this system. The shaft was fixed over the
locations where the bearings will be located (while allowing rotation) as well as fully
fixed where the shaft brake will be located. The torque was applied on the rollers. The
12
maximum von Mises stress experienced by the shaft when subjected to a torque of 10
in*lbs was 829 psi which is negligible compared to the yield strength of 73240 psi of the
aluminum shown in Fig. 5. This stress occurred in the region between where the shaft
brake will be mounted and where the closest bearing is mounted (see Fig. 6). The
maximum displacement of the system was equal to 0.007891 inches (shown in Fig. 7)
which occurred on the roller material and is considered negligible for the purposes of
this system. Since the safety factor with respect to torsion is so high the diameter of 0.5
inch was found to be sufficient.
Figure 5: von Mises Plot of Roller Assembly
Figure 6: Maximum von Mises of Shaft
13
Figure 7: Deformation of Roller System with Predicted Torque
Due to the fact that the torque value used in this initial FEA simulation was predicted
based off of values talked about on forums, the actual measured torque was a little
higher. The measured torque on the system was actually 14 in*lbs. A second FEA
simulation was run to show that the roller system could still handle this torque value. The
maximum von Mises stress on the shaft was found to be 1125 which is still well below the
yield stress of 73240 psi. The deformation plot showed that the maximum deformation of
the roller material was now 0.0183 inches but is still negligible. The Deformation of the
shaft itself was nearly non-existent. This result is shown in fig. 8 and 9 below:
Figure 8: Maximum von Mises Stress with Measured Torque
14
Figure 9: Maximum Deformation with Measured Torque
The lowest resonant frequency of the shaft was found to be 346.5 rad/sec which is 1.44
times higher than the highest rotational speed the shaft would be subjected to at 240
rad/sec or 2300 rpm. The resonant frequencies found in the simulation can be seen in
table 1. This first resonance frequency affects the roller itself and not the shaft as shown
in figure 10. Upon these results, it has been determined that the shaft will not experience
any excess vibration due to resonance.
Table 3: Resonant Frequencies of Roller Assembly
15
Figure 10: First Mode Shape of Roller Assembly
The needle bearings chosen for the shaft far exceed the requirements for this shaft in
order to ensure failure does not occur due to a lack of definitive motor power and
speed specification published by the manufacturer. In addition to exceeding
performance requirements, they were also an ideal bearing geometrically that would
allow for easy mounting to the frame. The bearings were purchased from SDPI and the
part # is A 7Z33-PB500N. These bearings are rated to allow for the 1/2” shaft, a maximum
speed of 22,000 rpm, and a max radial load of 380 lbf. Also, thrust bearings were
needed because the needle bearings do not hold the shaft in place laterally.
McMaster part #5909K310 and #5909K440 was used as a cheap and effective solution.
These are mounted between the plastic rollers and frame on each side.
High Density Polyethylene (HDPE) was chosen for the rollers due to cost and availability.
Two 5” diameter X 3” wide rods were purchased (McMaster part #8624K651). The 5-inch
diameter was chosen because it was the closest standard size to the diameter of the
Stampede tire which is 5.125”. This will allow for easier mounting of the car onto the
motor than a smaller roller as well as a similar rpm between the tire and the roller. A half
inch diameter holes were drilled through both of the rollers to allow them to fit over the
shaft. A magnet or bolt will be inserted into the side of the roller to allow for the rpm
sensor to detect RPM.
In order to securely mount the HDPE rollers onto the shaft, a custom shaft flange was
made for each roller. From 6061 aluminum stock, a disk shape flange was machined
and stepped down to a hub at its end. The flange has two holes where self-tapping
screws go through into the HDPE rollers, and the hub contains a set screw that drives
into the shaft (to prevent spinning and lateral movement).
16
Figure 11: Shaft FEA Free Body Diagram
Frame Assembly
Figure 12: Frame Assembly
The frame assembly (as shown in Fig. 12) is constructed mostly of 1” 80/20 aluminum
extrusions. The benefit to using this material is that allows the system to be highly
adjustable because mounted objects can slide down the mounting slots. This makes the
system more adaptable and customizable. The system is 21” long X 17” wide X 5” high.
Also, a 4” piece of 80/20 protrudes from the side of the 80/20, as shown in the above
figure. This is where the fan mounts which cools the shaft brake. A small piece of
17
aluminum sheet metal is used to mount the fan to the 80/20. Lastly, the top of the frame
is outfitted with a clear polycarbonate sheet to support the front wheels of the RC car.
In order to secure the RC car to the frame during testing, it has to be strapped down to
prevent forward-backward, side-side, and up-down movements. The rear wheels of RC
car is placed on the top most point of the HDPE rollers while the front wheels rest on the
plastic sheet. A traditional “X” shape strapping method was used at the front and the
back of the RC car. At the front, “S” hooks attach to the bumper and metal wire cable,
the cable then attaches to the front side of the front legs of the frame via wing nut and
washers for the cable to rest between. At the back, “S” hooks attach to the lower
control arms and metal wire cable, the cable then attaches to the back side of the
back legs of the frame via wing nut and washers for the cable to rest between. The
frame dimensions allow for a shallow mounting straps angle to allow for more of a
horizontal component of tension in the cables.
Figure 13: Front Mounting Method
18
Figure 14: Rear Mounting Method
Load Absorption Design
Regular dynamometers use an inertial load, an absorption brake, or a combination of
the two in order to measure power of the vehicle under test. In this application the load
absorption is performed by the Shaft Brake. The brake clamps on the shaft similar to a
Figure 15: Shaft Brake Mounted (highlighted)
19
regular shaft collar. As the vehicle under test spins the drivetrain, the clamping force of
the brake on the shaft would cause the brake to spin. However, the TAL220 load sensor
blocks rotational motion of the brake through the moment arm. The TAL220 load sensor
measures force applied, which is then used to calculate the torque of the vehicle
under test. The clamping force is gradually increased, sweeping the vehicle through its
entire rpm range for torque measurement overall.
The design of the shaft brake is shaped by variables such as: input power, application &
distribution of clamping force, interface with the load sensor, and cooling.
The final brake design is a simple 4 part mechanism. Two 6061 aluminum bodies hold
friction inserts on the shaft. Two springs in series are compressed by a hand lever with
1.71 mechanical advantage, providing a maximum 137.82 lbs. of clamping force. This is
translated to friction force by the 𝜇 = 0.32 coefficient of friction of the Kevlar nylon
composite inserts. This friction force transmits torque from the vehicle under test through
the brake moment arm to the TAL 220 load sensor.
The Length of the moment arm has a direct correlation to the magnitude of the load on
the sensor. The equation for torque is: 𝑇 = 𝐹 ∗ 𝑑, so the force generated at a distance
from the center of the shaft is 𝐹 =𝑇
𝑑. The smaller the moment arm length (d), the greater
the force. The final design employs a 2” moment arm, therefore provide a 2x reduction
in torque transmitted to the load sensor. A free body diagram showing this can be seen
in fig. 16.
Figure 17: Spring Selection
Manf. P/N
outside
diamete
r (inch)
free
length
(inch)
solid
length
(inch)
Travel
(inch)
spring rate
K
(lbs/inch)
Maximum
lbf/spring
LHP 072E 02S 0.375 0.5 0.364 0.136 506.7 68.9112
Spring Selection
Figure 16: Free Body Diagram of Shaft Brake-Load Sensor Interface
20
Clamping Method
The clamping force is provided by two springs in series, specified in figure 17. Two springs
are compressed by a hand brake, allowing for a consistent and measurable force
application. The springs are held captive in a nylon sleeve. As the handbrake is
depressed the cable pulls an aluminum cylinder down through the nylon sleeve,
compressing the springs.
The brake lever provides roughly a 1.71 factor of mechanical advantage, allowing 80
lbs applied at the lever to generate 137 lbs on the springs. The clamping force required
for a complete dyno trial is less than 95lbs at the clamp. An average males grip strength
is roughly 80 lbs, and 95lbs through a 1.71 mechanical advantage is 55 lbs.
Figure 18: Fabrication Process
Figure 19: Brake Clamping Method
Figure 20: Brake Lever Diagram
21
Shaft Brake Loading FEA
Stress and Displacements
Figure 21: Shaft Brake von Mises and Displacement Plots
Solidworks FEA confirms that there are no critical stresses in the shaft brake itself and
any Deflection is negligible. The following conditions were applied:
The Von Mises stress plots shows where max stress begins to occur. Considering the
direction of the clamping force, it is assumed these areas are in tensile stress. The
outside surface is in tension from being clamped over the shaft. The four corners where
the friction material meets the aluminum body show tensile stress from the way the
body is clamped over the friction insert.
By plotting the first principal stress and applying the iso-clipping tool, it can be
confirmed that these areas are indeed in tensile stress.
FEA Conditions:
Torque on shaft: 14 𝑖𝑛 ∗ 𝑙𝑏𝑠
Bolt1,2 axial forces 5 𝑙𝑏𝑠, 138 𝑙𝑏𝑠
Coefficient of Friction: 𝜇 = 0.32
6061-T4 Yield Strength: 32999 𝑝𝑠𝑖 Inertial relief on shaft:
FEA Results
Max von Mises stress: 20360 𝑝𝑠𝑖 Max Deflection: 0.007923 𝑖𝑛𝑐ℎ
B1 B2
Figure 22: Iso-Clip of 1st Principal Stress. Areas in
Tension
22
Contact pressures
Performance of the shaft brake would be optimal with an even pressure distribution
over the shaft. An even pressure distribution around the shaft allows for consistent wear
at rubbing surfaces, and reduction in shaft deflection.
In the above plots, we are able to see that the loading magnitude (figure 24) and
contact pressure (figure 23) are much greater closer to the second bolt, which
simulates the 137lbs of clamping force. Uneven force application or operation with
dramatic uneven wear could lead to misalignment or vibration issues. Life testing would
be suggested to evaluate the effects of uneven wear.
CFD analysis
Shaft Brake CFD
As the motor of the design origin vehicle is a 25watt motor, it is safe to assume that the
heat generated at the braking surface is 25watts.
CFD Conditions:
Input Power: 25 𝑤𝑎𝑡𝑡𝑠
Fan Capacity 84 𝐶𝐹𝑀, 20.3𝑓𝑡
𝑠
Ambient Temperature: 𝑇 = 70𝑜𝐹
CFD Results
Max Temperature 200𝑜𝐹
Max Heat Flux Achieved: 18.75𝑘𝑊
𝑚2
Max Deflection: 0.007923”
Figure 25: Air Temperature and Shaft Surface Heat Flux
Figure 24: Shaft Brake Load Magnitude Scaling Figure 23: Contact Pressures on Shaft
Figure 26: Shaft Brake Surface Temperature
23
CFD analysis shows that the resulting temperature will be roughly 200𝑜𝐹, well below the
300𝑜𝐹 working temperature of the friction material (discussed in next section). However,
it is still desirable to cool the brake via fan in order to keep variables affecting power
readings as consistent as possible.
Vehicle Motor CFD
As the motor of the design origin vehicle is a 25watt motor, it is assumed that 25W of
heat is being generated at the surface of the motor.
Friction Material
Selection of the Friction material was based on the following criteria:
Wear resistance
Friction Coefficient
Temperature sensitivity
Material property stability
Friction Coefficient
Lower friction=higher required clamping force
Selected Material:
Reasoning for choosing Kevlar/Nylon Composite:
Low material cost: $0.000356
ℎ𝑜𝑢𝑟 runtime cost.
Highest Wear Resistance
Highest high friction coefficient
300𝑜𝐹 working temperature
Low Thermal Expansion Coefficient
Other Materials Considered:
Nylon 6/6 | Delrin© | PTFE | Abrasion Resistant UHMW.
Material
friction
coeff
density
(lbs/in^3)
thermal
expansion
(in/in/F)
Specific Heat
(j/kgC)
max working
temp
wear resistance
(in^3 min/ft*lbs*hr)*10^-10
Kevlar filled nylon (Hydlar Z) 0.32 0.042 1.60E-05 1700.00 300 80
CFD Conditions:
Input Power: 25 𝑤𝑎𝑡𝑡𝑠
Fan Capacity 84 𝐶𝐹𝑀, 20.3𝑓𝑡
𝑠
Ambient Temperature: 𝑇 = 70𝑜𝐹
CFD Results
Max Surface Temperature 105𝑜𝐹
Table 4: Kevlar Fill Nylon Properties
24
Wear Rate Calculations
Material Wear rate is generally designated by Wear Factor, K (𝑖𝑛3𝑚𝑖𝑛
𝑓𝑡∗𝑙𝑏𝑠∗ℎ𝑟∗ 10−10). Wear
Factor data is produced according to ASTM D3702 “thrust washer” wear test. The Wear
Factor itself is determined by the equation: 𝑊 = 𝐾𝐹𝑉𝑇 [7]
Where: 𝑊 = 𝑤𝑒𝑎𝑟 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑖𝑛3), 𝐾 = 𝑤𝑒𝑎𝑟 𝑓𝑎𝑐𝑡𝑜𝑟 (𝑖𝑛3𝑚𝑖𝑛
𝑓𝑡∗𝑙𝑏𝑠∗ℎ𝑟∗ 10−10)
𝐹 = 𝑁𝑜𝑟𝑚𝑎𝑙 force (𝑙𝑏𝑠), 𝑉 = 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑠𝑝𝑒𝑒𝑑 (𝑓𝑡
min) , 𝑇 = 𝑒𝑙𝑎𝑝𝑠𝑒𝑑 𝑡𝑖𝑚𝑒(ℎ𝑟𝑠).
Kevlar/Nylon Composite Wear Properties:
𝑊𝑒𝑎𝑟 𝐹𝑎𝑐𝑡𝑜𝑟: 𝐾 = 80 𝑖𝑛3𝑚𝑖𝑛
𝑓𝑡∗𝑙𝑏𝑠∗ℎ𝑟∗ 10−10[4] 𝑆𝑒𝑟𝑣𝑖𝑐𝑒 𝑣𝑜𝑙𝑢𝑚𝑒: 𝑊𝑓 = 0.1322𝑖𝑛3
𝑅𝑢𝑛 𝑡𝑖𝑚𝑒 𝑡𝑖𝑙𝑙 𝑠𝑒𝑟𝑣𝑖𝑐𝑒: 𝑇 =𝑊𝑓
𝐾𝐹𝑉=
0.1322𝑖𝑛3
80𝑖𝑛3𝑚𝑖𝑛
𝑓𝑡 ∗ 𝑙𝑏𝑠 ∗ ℎ𝑟∗ 1010 ∗ 50𝑙𝑏𝑠 ∗ 308
𝑓𝑡𝑚𝑖𝑛
= 1073.1 𝐻𝑜𝑢𝑟𝑠
Cost of material: 1.25”dia, 12”L, $42.65. Material cost per unit runtime $0.000356
ℎ𝑜𝑢𝑟.
Bill of Materials Table 5: Bill of Materials
BILL OF MATERIALS
ITEM
NO.
PART NUMBER DESCRIPTION MANF. PART # H Position
2.0T/QTY.
1 10001 8020 EXTRUSION 15" MCMASTER
47065T412
3
2 10002 8020 EXTRUSION 21" MCMASTER
47065T412
2
3 10003 8020 EXTRUSION 4" MCMASTER
47065T412
4
4 10010 TOP PLATE NA 1
5 60003 PRX102-8P MOUNT
ASSM.
NA 1
5.1 10004 RPM BRACKET MCMASTER
1556A240
1
5.2 20001 RPM SENSOR PRX102-
8P
OMEGA
PRX102-8P
1
5.3 hex nut jam_am M8X1.25 Jam Nut MCMASTER
94223A102
2
6 60004 80/20 CORNER
BRACKET ASSM.
MCMASTER
47065T239
10
6.1 20002 80/20 CORNER
BRACKET
NA 1
25
6.2 60005 80/20 T-SLOT FASTENER
ASSM.
MCMASTER
47065T139
4
7 20003 WASHER FOR 1/4"
SCREW
MCMASTER
92141A029
6
8 60005 80/20 T-SLOT FASTENER
ASSM.
MCMASTER
47065T139
9
9 60006 80/20 T-SLOT FASTENER
ASSM, LONG
NA 4
9.1 20004 ROUND HEAD PHILLIPS
1/4"-20 X 5/8"
MCMASTER
91773A539
1
9.2 20005 80/20 T-SLOT NUT MCMASTER
47065T139
1
10 60008 LOAD SENSOR MOUNT
ASSM.
NA 1
10.1 10011 LOAD SENSOR
BRACKET
NA 1
10.2 20009 LOAD CELL TAL220 1
10.3 socket head cap
screw_am
M5 X 0.8mm SOCKET
HEAD SCREW
MCMASTER
91290A222
2
10.4 socket button
head cap
screw_ai
1/4"20 X .625 SOCKET
CAP SCREW
MCMASTER
98164A212
3
11 60002 ROLLER SHAFT ASSM. NA 1
11.1 10005 1/2" DIA ALUM. SHAFT MCMASTER
9063K16
1
11.2 10006 5" DIA X 3" LNG.
ROLLER
MCMASTER
8624K651
2
11.3 20006 0.5" MOUNTED PILLOW
BEARING
SDPI A 7Z33-
PB500N
2
11.4 10013 ROLLER FLANGE NA 2
11.5 socket set screw
cup point_ai
5/16"-18 CUP SET
SCREW
MCMASTER
92313A575
2
11.6 10014 1/4-20 SELF TAPPING
SCREW
MCMASTER
91715A172
4
11.7 60009 THRUST BEARING
ASSM.
NA 2
11.7.1 10015 1/2" THRUST BEARING MCMASTER
5909K310
1
11.7.2 10016 0.032" THICK WASHER
FOR 1/2" DIA. SHAFT
MCMASTER
5909K440
2
11.8 10017 SHAFT COLLAR MCMASTER
6435K14
2
11.9 20012 1/4" DIA MAGNET MCMASTER
58605K35
1
12 60007 SHAFT BRAKE ASSM. NA 1
26
12.1 10007 SHAFT BRAKE BOTTOM NA 1
12.2 10008 SHAFT BRAKE TOP NA 1
12.3 10009 FRICTION MATERIAL
INSERT
MCMASTER
8502K48
2
12.4 20007 SPRING BUSHING MCMASTER
98180A180
3
12.5 20008 SHAFT BRAKE SPRING LEE LHP072E02S 2
12.6 socket head cap
screw_ai
8-32 X 1" SOCKET CAP
SCREW
MCMASTER
91251A199
1
12.7 flat washer type b
narrow_ai
0.19" ID WASHER MCMASTER
98180A190
2
12.8 lock washer spring
regular_ai
0.2" SPLIT LOCK
WASHER
MCMASTER
92147A430
2
12.9 socket head cap
screw_ai
10-32 X 2.75" SOCKET
CAP SCREW
MCMASTER
91251A359
1
12.1 machine screw
nut hex_ai
10-32 NUT MCMASTER
96537A160
1
13 60010 FAN MOUNT ASSM. NA 1
13.1 10003 8020 EXTRUSION 4" MCMASTER
47065T412
1
13.2 60004 80/20 CORNER
BRACKET ASSM.
MCMASTER
47065T239
1
13.2.1 20002 80/20 CORNER
BRACKET
NA 1
13.2.2 60005 80/20 T-SLOT FASTENER
ASSM.
MCMASTER
47065T139
4
13.3 60011 80mm FAN
80X80X38mm
VANTEC
TD8038H
1
13.5 60005 80/20 T-SLOT FASTENER
ASSM.
MCMASTER
47065T139
2
27
Drawings
Figure 27: Part #10001 - 8020 Extrusion 15"
28
Figure 28: Part #10002 - 8020 Extrusion 21"
29
Figure 29: Part #10003 - 8020 Extrusion 4"
30
Figure 30: Part #10004 - RPM Bracket
31
Figure 31: Part #10005 - 1/2" Dia Alum. Shaft
32
Figure 32: Part #10006 - 5" Dia X 3" Lng Roller
33
Figure 33: Part #10007 - Shaft Brake Bottom
34
Figure 34: Part #10008 - Shaft Brake Top
35
Figure 35: Part #10009 - Friction Material Insert
36
Figure 36: Part #10010 - Top Plate
37
Figure 37: Part #10011 - Load Sensor Bracket
38
Figure 38: Part #10012 - Fan Bracket
39
Figure 39: Part #10013 - Roller Flange
40
Figure 40: Assembly #60001 - Frame Assm.
41
Figure 41: Assembly #60002 - Roller Shaft Assm.
42
Figure 42: Assembly #60002 - Roller Shaft Assm. Exploded View
43
Figure 43: Assembly #60007 - Shaft Brake Assm.
44
Figure 44: Assembly #60010 - Fan Mount Assm.
45
Instrumentation The instrumentation and data acquisition (DAQ) system for this project contains two
sensors, one amplifier board, one Arduino Uno microcontroller, and a Laptop or PC with
LabVIEW installed. Figure 45: DAQ System Diagram shows a diagram of the system
architecture.
Figure 45: DAQ System Diagram
To gather force data, a TAL220 parallel beam load cell is used
in conjunction with a separate HX711analog-to-digital
amplifier board. The load cell, shown in Figure 46: TAL220 Load
Cell, uses four separate strain gauges arranged in a
Wheatstone bridge formation to measure deflection across
the sensor. The Wheatstone bridge formation allows very small
changes in voltage to be detected by the HX711 amplifier
board. The amplifier board reads analog voltage values from
the load cell, then converts the analog value to a digital
Figure 46: TAL220 Load Cell
46
integer value through a 24-bit analog-to-digital converter (ADC).
RPM measurement is accomplished using a PRX-102-8N hall effect sensor which detects
proximity of ferrous metals. In order to use this sensor to measure RPM, a neodymium
magnet is pressed into the side of the roller so that each revolution is indicated by a rise
in voltage on the appropriate Arduino I/O pin. The Arduino keeps track of the period of
each revolution of the roller and calculates a running average period value (in
milliseconds) from the last 3 revolutions.
The software in the DAQ system involves two separate systems which communicate via
a serial data connection. The Arduino microcontroller offers its own integrated
development environment (IDE) and language based on C. This IDE is used to develop
code which is written to the board and executes continuously, sending data to the PC
every 100 milliseconds. The data is sent by a string of the form “RXXXXFXXXX,” where the
“R” and “F” characters are followed by the period and force values (represented by
“XXXX”), respectively. New line and carriage return characters are included at the end
of the string to serve as stop characters.
Once the data has been successfully sent to the PC, a LabVIEW VI is used to receive,
interpret, and display the data on the PC side of the system. While the Arduino’s primary
purpose is to sample raw data from the force sensor and keep track of period values,
the LabVIEW VI on the PC serves the purpose of decoding data, calculating final
values, and displaying information in real-time on the PC screen. The LabVIEW VI works
by reading the incoming string, separating it into values based on the format described
in the above paragraph, and performing calculations on the separated values.
Functionality within the VI includes real-time display of RPM, torque and speed values,
force sensor tare (zero) button, maximum power readout, and real-time graphic display
of data. Data is also able to be exported through the graphic displays after the end of
a run. Figure 49: Screenshot of LabVIEW VI shows the VI after a test run. For wiring
information, reference Figure 50: Instrumentation Wiring. See Appendix E for LabVIEW
block diagrams.
Figure 48: Assortment of
Hall Effect Sensors
Figure 47: TAL220 load sensor
(highlighted)
47
Figure 49: Screenshot of LabVIEW VI
Figure 50: Instrumentation Wiring
For future work, several aspects of the instrumentation/DAQ system can be improved.
Recommendations include taking steps to make the data transfer string more robust,
using lower cost hall effect sensor, and creating electromagnetic shielding around the
system to reduce noise and interference.
48
Calculations Ultimately, calculations for load cell force and clamping force on the rotating shaft
were determined to design and buy particular components. Before this could occur,
research was completed to find the power, drive gear ratio, and top speed of the RC
car1.
Using the known RC car tire diameter, the rollers and shaft diameters were integrated
into excel as inputs. Tire and roller torque were then found along with their respective
RPM’s as seen in Table 6:
Table 6: Basic RC Car Calculations
Tire torque was found using Eq. (1):
𝑇𝑡𝑖𝑟𝑒 = 𝑇𝑒𝑛𝑔𝑖𝑛𝑒 ∗ 𝑅𝑎𝑡𝑖𝑜𝑔𝑒𝑎𝑟 (1)
Roller torque was found using Eq. (2):
𝑇𝑟𝑜𝑙𝑙𝑒𝑟 = 𝑇𝑡𝑖𝑟𝑒 ∗𝐷𝑖𝑎𝑟𝑜𝑙𝑙𝑒𝑟
𝐷𝑖𝑎𝑇𝑖𝑟𝑒 (2)
Maximum tire RPM was calculated using Eq. (3):
𝑅𝑃𝑀𝑡𝑖𝑟𝑒 = 𝑆𝑝𝑒𝑒𝑑𝑚𝑎𝑥 ∗𝑅𝑒𝑣
𝜋 ∗ 𝐷𝑖𝑎𝑡𝑖𝑟𝑒 (3)
Maximum roller RPM was calculated using Eq. (4)
𝑅𝑃𝑀𝑟𝑜𝑙𝑙𝑒𝑟 =𝜋 ∗ 𝐷𝑖𝑎𝑡𝑖𝑟𝑒 ∗ 𝑅𝑃𝑀𝑡𝑖𝑟𝑒
𝜋 ∗ 𝐷𝑖𝑎𝑟𝑜𝑙𝑙𝑒𝑟 (4)
With these inputs, the moment arm design on the shaft brake was calculated. A load
has to be read on the load cell that is impacted by the moment arm of the shaft brake.
Since force is a function of torque and length, the principle was applied as seen in
Table 7.
49
Table 7: Moment Arm Force
Moment Arm Force Calculations
Torque, Shaft (in-lbf) 9.51
Moment Arm Length (in) 2.00
Force (lbf) 4.75
Rubbing Speed (in/s) 61.60
Rubbing Speed (m/s) 1.56
The moment arm length was made as an input in excel and torque was previously
calculated on the rollers. Since the rollers and the shaft are directly connected (not
geared together), the roller and shaft torques are equal. Equation (5) was used to find
the force on the moment arm. Since the load cell is rated for 11 lbs, a moment arm
length of 2 inches was chosen to result in a force of 4.75 lbs on the load cell. Ideally, you
should be using the middle of the range of the sensor so this is why this length of a
moment arm was chosen.
𝐹𝑙𝑜𝑎𝑑.𝑐𝑒𝑙𝑙 =𝑇𝑠ℎ𝑎𝑓𝑡
𝐿𝑚𝑜𝑚𝑒𝑛𝑡.𝑎𝑟𝑚 (5)
After this, the clamping force of the shaft brake was found. Table 8 shows calculations
to obtain this value.
Table 8: Shaft Brake Calculations
50
Using inputs of coefficient of friction and the force of the rotating shaft on its outer
surface, the clamping force on the shaft by the shaft brake was found using Eq. (6)2:
𝐹𝑐𝑙𝑎𝑚𝑝𝑖𝑛𝑔 =𝐹𝑠ℎ𝑎𝑓𝑡
𝜇 ∗ 𝑛 (6)
Where Fshaft is the force of the shaft at its surface, 𝜇 is the friction coefficient, and n is the
number of friction faces.
The force of the shaft was found using Eq. (7):
𝐹𝑠ℎ𝑎𝑓𝑡 =𝑇𝑠ℎ𝑎𝑓𝑡
𝐷𝑖𝑎𝑠ℎ𝑎𝑓𝑡 (7)
The clamping pressure was found using Eq. (8):
𝐹𝑠ℎ𝑎𝑓𝑡 =𝐹𝑐𝑙𝑎𝑚𝑝𝑖𝑛𝑔
𝑆𝐴𝑠ℎ𝑎𝑓𝑡 (8)
As long as the shaft brake clamping pressure is less than the braking material’s specified
maximum operating pressure, the system is safe. Other variables including thermal
effects of each material will be investigated to choose a final braking material.
Instrumentation Setup Procedure The following directions detail how to set up the instrumentation system.
1. Ensure that LabVIEW VI is open on the PC, but not running.
2. Plug in USB cable to Arduino Board.
3. Plug in USB cable to PC.
4. In the VI, select appropriate COM port under the “Resource Name” drop-
down menu.
5. Start the program by pressing the arrow button in LabVIEW.
6. Ensure that program is running by pressing the load cell and observing for
movement in the Torque reading on the VI.
Calibration Procedure Once the mechanical and electrical assemblies have been set up, calibration will
begin to dial-in the RC dyno. The goal is to ensure systems are working properly before
testing the RC car.
7. Ensure mechanical components are secure, including RC car to the
dynamometer.
8. Ensure the electrical components are secure and live, and test the sensors to
ensure accurate readings are registering in LabVIEW.
a. Force sensor: place known weights on force sensor and compare it to
the LabVIEW read-out. Adjust LabVIEW as necessary and test another
weight and ensure LabVIEW is correct.
51
b. RPM Sensor: bring car to maximum rpm and use a timing light to
compare its RPM read-out to LabVIEW RPM read-out. Adjust LabVIEW
as necessary and test another RPM to ensure LabVIEW is correct.
9. Without the shaft brake engaged, turn on the RC car and spin wheels to
ensure the car stays stationary on the frame and rollers. Also ensure sensor
RPM is being displayed in LabVIEW.
10. Bring RC car up to full speed (wide open throttle) and compare sensor RPM
to approximately known RC car wheel RPM. Calibrate until RPM sensor reads
the correct RPM.
11. While at WOT (wide open throttle), slightly engage shaft brake by tightening
adjustment fastener. Do this until car speed slightly decreases. Do not change
anything and wait for 2 seconds so data is displayed in LabVIEW. This data
point on a LabVIEW plot is the maximum power of the RC car at that
particular RPM.
12. Stop the system and analyze the torque and power plots in LabVIEW.
Determine if the power generated at that RPM makes sense.
a. If not: make adjustments to LabVIEW and RC dyno and repeat steps 4
and 5.
b. If so: follow the following testing procedure.
Testing Procedure
Once calibration has been completed, testing will begin to generate Torque and
Power vs RPM plots of the RC car. The goal is to ensure repeatability of the plots.
1. Ensure mechanical components are secure, including RC car to the
dynamometer.
2. Ensure the electrical components are secure and live.
3. Ensure that there is no force on the load cell, then press the “Tare” button in
the VI.
4. Without the shaft brake engaged, bring RC car up to full speed (wide open
throttle).
5. Slightly engage shaft brake by tightening adjustment fastener at a slow and
constant rate. Continue to do so until wheel slip occurs or the RC car stops.
13. Analyze the torque and power plots in LabVIEW and determine if the power
generated at that RPM makes sense.
a. If so: repeat steps 3 & 4 for five test runs. Use the same braking method
for each run.
b. If not: repeat the testing procedure. If this does not work, repeat the
calibration procedure, and then the testing procedure.
14. Once the five runs are completed, compare the torque and power plots. If
they are approximately the same, the dynamometer is determined
repeatable.
15. Save each LabVIEW Torque and Power vs RPM plots for reference
52
Results
Figure 51: Test 1 Results
53
Figure 52: Test 2 Results
54
Figure 53: Test 3 Results
55
Figure 54: Test 4 Results
56
Discussion of Results After the dynamometer was calibrated and initial testing was completed, Torque vs
RPM and Power vs RPM plots were generated. When the RC car declined in speed as
the brake was applied, force and RPM data was sent live from the force and RPM
sensors to the PC LabVIEW interface. Once the data was exported to excel, it was
graphically represented for analysis. The official results of Test 1 are tabulated in the
Appendix C and are represented in Fig. 51.
Maximum wheel power is 0.09 Horsepower (HP) at 870 RPM and maximum wheel torque
is 14.275 in-lb at 211 RPM. The wavy curves as seen in Fig. 51 are present for multiple
reasons. First, the drivetrain had a slight wobble due to a slightly bent shaft. That
translates to inconsistent loading from the RC wheels to the rollers of the drivetrain, and
also cyclical loading from the shaft brake to the load cell. Also, tolerances of the rollers
and flanges are not very high for circularity, concentricity, position, and
perpendicularity. This is due to the limitations of the machinery that was at hand.
The results seen in Fig. 51 match that of a typical DC motor, as Fig. 55 shows:
Figure 55: Typical DC Motor Plot
The RC car, powered by a DC motor, follows the same power and torque trends which
is expected. The power curve follows a parabolic shape, peaking at approximately half
of its top speed, while torque linearly decreases as speed increases. Figure 52, 53, 54
are other test runs that were completed and show similar trends as Fig. 55.
The test results other than Test 1 are not the same as in Test 1 for multiple reasons. Testing
was done on different days with different variables. Weather was different and
strapping method and force was not exactly the same. Also, the RC car had “wheel
slip” occur during some of these runs where the RC wheels would spin on the rollers of
the drivetrain. This had an effect on the results because the force of the wheels was not
directly translated to rolling motion.
57
Conclusion The goal according to the project objective was “to build a 2wd mechanical braking
dynamometer that measures chassis horsepower, with data output to a PC interface, of
a Traxxas Stampede or equivalent RC vehicle and is easy for the average hobbyist to
use.” This team met all these requirements and more. A 2wd mechanical braking
dynamometer was created, the system measures horsepower and torque, data is
exported to a PC interface, a Traxxas Stampede can be used on the dyno, and it is an
easy to use system. Torque measurement was incorporated into the dynamometer
because it is another important statistic for enthusiasts to know.
It was found through testing that the original torque value calculated for the system
was a little lower than the actual measured torque value. The original torque value
calculated for the system was 10 in*lbs whereas the measured value was 14 in*lbs. The
result on the design of the system was negligible, however care should be taken in the
future to be more conservative when estimating a value such as this. The value was
originally estimated off of forum posts because commercial data pertaining to the
power of the motor was not available.
This team encourages another group of student engineers to build upon this project to
make it work more effectively. The following are recommendations for the future to
optimize the RC Dyno’s performance.
Recommendations After designing and building the RC dynamometer, there are a few recommendations
for the future that would optimize the performance of the dyno in regards to
manufacturing and use.
- Use a steel shaft for the drivetrain: the current aluminum shaft slightly bent
during assembly (weak) and it galls when brakes apply (“dirty” metal).
- Reduce moment of inertia of the shaft: the current drivetrain his heavy (rollers
and flanges) which affects acceleration of the RC car. Design lighter rollers and
flanges.
- Use pillow block bearings with set screw: the current bearings are needle
bearings and not hold the shaft into place laterally. Thrust bearings had to be
used as a result (more assembly and more cost).
- Standardize testing procedure further: testing was completed on different days
which yielded different results. To minimize changes in variables, it is best to run
all tests during one day or carry over consistent variables to the next test day (i.e.
same temperate and humidity, same strapping method and force, etc.).
58
References [1] "12T Motor RPM." Traxxas. N.p., 13 Apr. 2009. Web. 1 June 2016.
<https://traxxas.com/forums/showthread.php?469305-How-many-RPM-is-a-12T-
motor>.
[2] Budynas, Richard G., and J. Keith Nisbett. Mechanical Engineering Design. 10th ed.
New York: McGraw Hill, 2014. Print.
[3] “Hand Grip Strength Test” Topend Sports. N.p. 2016. Web.
<www.topendsports.com/testing/tests/handgrip.htm>
[4] "Engineering 185°F - 300°F | Nylon - Extruded Type 66." Ensinger Inc. N.p., 2016. Web.
<http://www.ensinger-inc.com/products.cfm?page=product&product=hydlar+z+-
+aramid+(kevlarandreg;)+fiber+filled>.
[5] James Von Horn, 2016, “RC Brushless Chassis Dyno.”
<http://www.mcpappyracing.com/dyno.php>
[6] Mark Catchpole, 2014, “Chassis Dyno – Which is Best?”. http://www.tdi-
plc.com/chassis-dyno-best/
[7] "Wear Resistance Data." RTP Co. N.p., 2015. Web.
<http://web.rtpcompany.com/info/wear/0200/english.htm>.
[8] Winther, J. B. (1975). Dynamometer Handbook of Basic Theory and
Applications. Eaton Corporation, Cleveland, Ohio.
lix
Appendix
Appendix A: Test 1 Results
RPM - Plot 0
Torque - Plot 0 RPM - Plot 0
Horsepower - Plot 0
1.814 1154 0.033
1154 1.786 1154 0.033
1154 1.716 1154 0.031
1154 1.759 1154 0.032
1154 1.86 1154 0.034
1154 1.886 1154 0.035
1154 1.896 1154 0.035
1154 1.804 1154 0.033
1154 1.756 1154 0.032
1154 1.753 1154 0.032
1154 1.747 1154 0.032
1154 1.737 1154 0.032
1154 1.73 1154 0.032
1154 1.722 1154 0.032
1176 1.771 1176 0.033
1154 1.914 1154 0.035
1154 2.031 1154 0.037
1154 2.117 1154 0.039
1154 2.166 1154 0.04
1132 2.299 1132 0.041
1132 2.451 1132 0.044
1132 2.727 1132 0.049
1091 3.072 1091 0.053
1091 3.32 1091 0.057
1071 3.565 1071 0.061
1053 4.022 1053 0.067
1034 4.264 1034 0.07
1017 4.564 1017 0.074
1017 4.798 1017 0.077
1000 4.883 1000 0.077
984 5.023 984 0.078
968 5.229 968 0.08
952 5.326 952 0.08
938 5.395 938 0.08
923 5.588 923 0.082
lx
909 6.074 909 0.088
882 6.329 882 0.089
870 6.532 870 0.09
845 6.623 845 0.089
833 6.723 833 0.089
822 6.867 822 0.09
789 6.967 789 0.087
759 7.015 759 0.085
750 7.088 750 0.084
732 7.255 732 0.084
723 7.713 723 0.088
706 7.664 706 0.086
682 7.653 682 0.083
674 7.694 674 0.082
659 7.792 659 0.082
652 7.936 652 0.082
638 8.059 638 0.082
632 8.223 632 0.082
619 8.507 619 0.083
606 8.673 606 0.083
594 8.719 594 0.082
583 8.745 583 0.081
571 8.811 571 0.08
556 8.903 556 0.078
556 9.054 556 0.08
545 9.413 545 0.081
536 9.966 536 0.085
526 9.991 526 0.083
513 9.977 513 0.081
504 10.099 504 0.081
504 10.154 504 0.081
492 10.054 492 0.078
484 9.977 484 0.077
476 10.18 476 0.077
465 10.477 465 0.077
465 10.593 465 0.078
455 10.526 455 0.076
444 10.551 444 0.074
444 10.697 444 0.075
429 10.931 429 0.074
411 11.31 411 0.074
lxi
411 11.251 411 0.073
395 11.21 395 0.07
375 11.376 375 0.068
375 11.592 375 0.069
355 11.964 355 0.067
355 11.875 355 0.067
333 11.577 333 0.061
333 11.502 333 0.061
316 11.705 316 0.059
316 11.931 316 0.06
300 11.956 300 0.057
300 12.113 300 0.058
286 12.355 286 0.056
286 12.613 286 0.057
286 13.438 286 0.061
270 13.408 270 0.057
270 13.083 270 0.056
252 12.977 252 0.052
252 12.876 252 0.052
252 13.211 252 0.053
230 13.023 230 0.048
230 12.978 230 0.047
230 12.994 230 0.047
211 13.036 211 0.044
211 13.559 211 0.045
211 14.111 211 0.047
211 14.275 211 0.048
194 13.962 194 0.043
194 14.023 194 0.043
194 13.887 194 0.043
180 13.541 180 0.039
180 13.532 180 0.039
180 13.558 180 0.039
180 11.753 180 0.033
180 4.35 180 0.012
180 0.547 180 0.002
180 0.422 180 0.001
180 0.431 180 0.001
180 0.408 180 0.001
180 0.402 180 0.001
180 0.4 180 0.001
lxii
180 0.388 180 0.001
180 0.379 180 0.001
180 0.381 180 0.001
180 0.396 180 0.001
180 0.404 180 0.001
180 0.406 180 0.001
180 0.418 180 0.001
180 0.382 180 0.001
180 0.372 180 0.001
180 0.374 180 0.001
180 0.368 180 0.001
lxiii
Appendix B: Team Contract
lxiv
Appendix C: Team Member Resumes
lxv
lxvi
lxvii
lxviii
Appendix D: Purchase Orders
lxix
lxx
lxxi
lxxii
lxxiii
lxxiv
lxxv
lxxvi
lxxvii
Appendix E: LabVIEW Block Diagrams
lxxviii
lxxix
