P16221: Formula SAE (FSAE) Shock Dynamometer

12th May 2016

James Holmes Christopher Batorski Aung Toejsh9567@rit.edu cjb6970@rit.edu axt1937@rit.edu

Salvatore Fava Andrew Doddsxf7661@rit.edu amd6505@rit.edu

Contents

1 Abstract 2

2 Introduction 2

3 Design Process 23.1 Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1.1 Actuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.1.2 Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.1.3 Safety Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2 Electrical/Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2.1 Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83.2.2 Load Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2.3 Infrared Sensor (IR Sensor) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2.4 Linear Potentiometer (L-Pot) . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2.5 Motor and Motor Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2.6 User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2.7 Arduino Software Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4 Conclusions 12

5 Future Works 12

6 Acknowledgements 12

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1 Abstract

Dampers (or shock absorbers) signi�cantly in�uence the vehicle dynamic properties of a racecar. Ashock dynamometer is a measurement device that can supply an input and measure the response(both displacement and force) of a damper. Understanding the characteristics of these dampersallows racing teams to make known design changes and �ne adjustments to the car to optimizeperformance. The project has developed a damper dynamometer to measure the dynamic charac-teristics of dampers used in various applications.

2 Introduction

The RIT Formula SAE(FSAE) Team competes in an international design competition based aroundsmall, open-wheel, single seater autocross cars. The team would like to better understand thedampers used on their car to have a competitive advantage against other schools. The best way tobetter understand and tune dampers is through the use of a shock dynamometer. At this point intime, the FSAE team does not have access to this equipment.

Understanding the characteristics of dampers on a racecar is important in being able to e�ect-ively and e�ciently tune the car. The RIT Formula SAE team would like to better understandthe dampers used on their car to have a competitive advantage against other schools. The bestway to better understand and tune dampers is through the use of a shock dynamometer. Thereare similar machines in the mechanical engineering building labs, however they do not meet thefrequency requirements, size constraints, and mobility requirements. The goal of this project is todesign a device to characterize dampers, that is capable of supplying a displacement input pro�leand measuring force and displacement responses of a damper.

3 Design Process

Dynamometer requires both mechanical and electrical components to work together. Mechanicalsystems provide movement mechanisms and linkages of di�erent mechanical components to havestable controlled movement structures. Software systems allow users to control mechanical systemsby providing an interface to enter desired commands, and displaying current system conditions(data collection). Software systems translate user commands into electrical signals by using amicro-controller to control mechanical movements and collect data samples.

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3.1 Mechanical

Figure 1: Full System Design

The goal of the mechanical system was to provide a rigid frame for multiple components to attachto as well as provide a mechanism to displace a damper at given speeds. For practical purposes,the mechanical system was split into two subsystems; frame and actuation. The ideal function ofthese systems was to build a stand that would not de�ect at all and develop an actuation systemthat would be capable of displacing the damper both using a standard displacement pro�le ora measured damper pro�le (from collected vehicle data). However, the customer requirements forthese systems were XXXin of de�ection per XXXlb load and an actuation system capable of variousstandard displacement pro�les, respectively. Below is a detailed list of customer requirements thatthe team agreed to meet.

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Figure 2: Design Calculations

3.1.1 Actuation

The main goals of the actuation system are to displace a damper at given velocities and accommod-ate dampers with ranges of travel from 1 to 7 inches. It must be capable of generating the forcenecessary to move the damper at the desired rates under both compression and rebound.

Due to the high load requirement that the team originally was trying to meet, a rotary systemwas selected as the actuation method. The �nal design was a 3hp electric motor. A crank is drivenby the motor that pushes a connecting rod up and down, displacing the damper. Each componentwas designed to support damper and dynamic forces with a factor of safety of 2. The damper itselfis supported at one end by a clevis attached to the load cell, and a carrier on a linear bearing atthe other. These components can be viewed below.

Figure 3: Rotary System Components

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In order to be able to adjust damper displacement, the crank pin was made to be removableand many di�erent positions were machined into the crank. Changing the displacement curve is aseasy as removing the pin and moving it to a di�erent crank pin location.Linear bearing and carrieranalysis is shown below.

Figure 4: Carrier Analysis

Figure 5: Linear Bearing Analysis

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Figure 6: Gearmotor Selection Graph

3.1.2 Frame

The goal of the dyno frame is to allow for the testing of a wide range of vehicle shock with eyeto eye distances ranging from 6 to 36 inches. The frame provides for ample space to contain theactuation and electrical systems while maintaining an OSHA safe work environment.. Frame designwas mostly sti�ness driven, A36 steel box tubing was selected for its sti�ness and low cost as wellas in�nite fatigue life. Most members of the frame were analyzed in bending, a factor of safety of2 was applied to all mechanical components.

Figure 7: Base De�ection Calculations

The feet of the frame were selected for its vibration absorption capability. An initial selection

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was made for the build cycle, selection will be validated by testing and updating vibration isolationequations with a �nal weight at the end of the build/test phase.

Figure 8: Base Isolator Sizing

Mast design was driven by o�-axis de�ection and buckling calculations. Engineering require-ments speci�ed a minimum o� axis de�ection of

Figure 9: Mast Design

3.1.3 Safety Enclosure

A safety enclosure around the shock being tested is needed to protect the user from unexpectedevents like moving parts breaking o�. 3 sides of the enclosure is �xed with one side door to allowthe user access to the shock for adjustment.

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Figure 10: Model Overview

3.2 Electrical/Software

The goals of electrical system are to create an interface between the user and microcontroller,to collect data, and to control the mechanical systems using electro-mechanical sub-systems. Toachieve the bridge between user and microcontroller, a custom user interface and custom commandinstructions are implemented. To collect data, sensors such as Infrared Sensor, Linear Potentiometerand load cell are used. To control mechanical movement, arduino IDE is used to develop controlstructure for motor control.

3.2.1 Microcontroller

Microcontroller is the main control unit of system. The design required a fast and powerful pro-cessing unit for data sampling, data calculations, actuation control and serial communication toPC. Arduino UNO and Arduino Due were considered for the system. Arduino UNO is a 5-V 8-bit16 MHz processing unit. UNO has maximum Analog-to-Digital (ADC) conversion resolution of 10bits. Arduino Due is a 3.3-V 32-bit 84MHz ARM core platform with 12 bits ADC. Figure 11 andFigure 12 show the two types of controller boards. Arduino Due is chosen based on factors such asprocessing power, ADC resolution, and up-gradability.

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Figure 11: Arduino UNO

Figure 12: Arduino Due

3.2.2 Load Cell

The push and pull forces of up to 1500 lbs on the shock absorber need to be measured duringtesting. The team was able to acquire a load cell that can measure up to 5,000 lbs of push or pull(donated by PCB Piezotronics). The speci�cations of the load cell more than required, however

the cost of a new load cell would have used 2/3 of the team's budget.

Figure 13: Load Cell

3.2.3 Infrared Sensor (IR Sensor)

The temperature of the shock body a�ects the response of a shock absorber. Therefore it needs to bemeasured. The FSAE team provided an infrared sensor produced by Texense. The team currentlyuses them to measure tire temperature of the race car. The sensor can measure up to 150° Celsiusat 20 cm away from the shock body. The shock dynamometer design requires temperatures to bemeasured up to 100° Celsius.

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Figure 14: IR Sensor

3.2.4 Linear Potentiometer (L-Pot)

Similar to IR sensor, the FSAE team uses linear potentiometers (L-Pots) to measure the lineardisplacement of the shock absorber as it compresses and rebounds during a race. The L-Potprovided by FSAE has a maximum stroke range of 2 inches. Other teams such as Baja and Hot-Wheelz have di�erent shock lengths requiring various stroke ranges. To accommodate that, theteam designed the system to allow the L-Pot to be easily changed. The user will have to enter themaximum stroke range of their particular L-Pot so that the software can control the linear shaftspeed accordingly.

Figure 15: Linear Potentiometer

3.2.5 Motor and Motor Controller

In order to compress the shock absorber at di�erent linear speeds, that generate forces up to 1,500lbs, we needed a strong motor. We decided on a 3-horsepower motor (Nord model SK-372.1) witha gearbox that has a 4.66:1 gear ratio. The gearbox rotates once for every 4.66 rotations of themotor shaft. This allows the motor to produce the forces necessary to compress the shock. Themotor uses 3-phase 208 volt power to operate.

Figure 16: Motor

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In order to control the speed of the motor the team decided on a PowerFlex 523 motor controllerfrom Allen Bradley. The motor is capable of starting under load and the motor controller is capableof operating this style of motor. The motor controller interfaces with the microcontroller and allowsit to remotely start, stop, and adjust the speed of the motor. The motor controller also monitorsthe health of the motor and will shut it o� if it overheats, or if it stalls out (such as if a catastrophicfailure occurs that jams the rotating parts of the dyno). The motor controller also monitors thesafety interlock switches and the emergency stop switch and will stop the motor if a door is openedor the stop button is pressed.

Figure 17: Motor Controllers

3.2.6 User Interface

The user interface software for the control of the dynamometer was written in C# using MicrosoftVisual Studio 2015. The software allows the user to input parameters for tuning their shocks. Thechart on the right side has a yellow line indicating the optimal response curve based on the decisionsof the shock designer. As the dynamometer runs, the live data from their shock will be plotted onthe same chart so that the operator can compare the actual data to their expected data and tunethe shock between runs.

Figure 18: User Interface

The users can save the parameters of the car and decision points into a text �le for re-use later.Di�erent car �les can be used based on individual track data for quick recall at a later time. The

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data that is collected during the run will also be saved to a comma separated value (CSV) �lefor post run analysis. The software can be changed from US Standard units to SI units based onoperator preference. The Damper Dyno Control software interfaces with the Arduino Due controllerusing RS-232C at 115,200 baud. This allows anyone to interface with the dynamometer withoutinstalling the Arduino drivers.

3.2.7 Arduino Software Design

Arduino IDE v1.6.8 is used to write software code-lines for communication, control and data pro-cessing. Arduino receives commands from PC User Interface. The detail command list can befound in Figure 19.

Figure 19: Arduino Command List

There are four phases in software design �ow. Zeroing load cell, �nding bottom dead center,shock warm-up and data sampling. Zeroing load cell is important to accurately calibrate the readingdue to the varying weights of the shocks. To protect linear potentiometer from being pulled apartby the motor, �nding bottom dead center is required. In this phase, the motor rotates slowly, whilesoftware reads L-Pot data. If the user did not mount the shocks and L-pots correctly, softwarewill detect the thresholds being hit and stop the motor. In warm-up phase, the program runs thesetup for a particular amount of time to emulate the temperature of the shock to be as close aspossible to real-time situation. In data sampling phase, software begins data sampling every 1mills-seconds and returns the averaged velocity and positive/negative force every second until therequired runtime is up.

4 Conclusions

This project is intended to help RIT racing teams understand the characteristics of their shockabsorbers. Understanding the characteristics of the shocks enable them to �ne tune the behaviorof the shock. As a result, the performance of the race cars increase, and ultimately winning therace. The dynamometer will also give students the opportunity to help them study the dynamicsof a shock dynamometer.

5 Future Works

As future works, electromagnetic actuator could be used to more accurately simulate track data asopposed to current �xed one speed design. Micro-controller takes a heavy load when it comes todata sampling and control variable calculations. It is important to sample fast enough to not missany important data points. Therefore, micro-controller should also be upgraded to the one that hasco-processor to share the computational load or two micro-controllers can be used, one to sampleand one to calculate.

6 Acknowledgements

Our thanks go to Gerry Garavuso for giving us guidance us through this project. Many specialthanks to

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� Alan Nye, RIT FSAE Faculty Advisor

� Ryan Crittenden, RIT FMS

� Brinkman Machine Tools Lab, CNC and Waterjet Time

� Smidgens Lasercutting

� Base SS panel cutting

� PCB Piezotronics, Loadcell

� Active Sensors, L Pot

� RBC Bearings, Actuation Bearings

� Samuel Specialty Metals, Aluminum Material

� Klein Steel Direct, Steel Material Mahany

� Welding Supply, Welding Supplies

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