Drivetrain User ManualME 498 - Spring 2021

Latest Revision: 5/12/2021Prepared by: Lucas Foulk

AbstractThis document is intended to detail the aspects of the drivetrain system that is used to provide power to the wheels of the FSAE car.

Table of ContentsExecutive Summary 2

Introduction 2Current State of Design 3

Cooling System Installation Guide 3How to Install 3Assembly/Disassembly 4

Future Team Recommendations 4

Executive SummaryIntroduction

The drivetrain of the 2021 FSAE car was designed with vehicle performance in mind. The ability to deliver the maximum power and efficiency, remain as light and stiff as possible were also major design considerations. The final drivetrain package is comprised of an Emrax 208 liquid cooled axial flux synchronous motor, eccentric rings for easy chain tensioning, motor shaft support bearings, a flex disc which allows for any angular misalignment of the motor shaft during load so as to protect the integrity of the internal Emrax bearings, and a limited slip differential to maintain rear wheel independence. A sleek 4 bolt mounting system allows the self-contained drivetrain assembly to easily be removed and installed on the chassis. The entire drivetrain assembly also maintains the ingress protection rating of IP65 in order to pass competition qualifying events. The Emrax 208 provides a nice coupling for a chain driven system, with a single gear ratio, 3:1. The gear ratio was optimized for acceleration and endurance of the vehicle during testing. The single motor connected to a limited slip differential provides the lightest possible configuration while maintaining the team's power output goals. Having the subsystem independent of the chassis of the car allows the team to conduct targeted testing and evaluate the functionality of the system prior to installation in the vehicle. Torque is transmitted from the motor through the flex disc to the motor shaft, which is press fit through a bearing support, and is then connected to a quick disconnect sprocket which provides the driving torque for the assembly. Due to drivetrain housing flexural issues in previous years, the housing which contains all of these components was optimized for rigidity, while maintaining a streamlined weight. A rigid housing was fundamental in order to increase stiffness and reduce vibration isolation which would further limit the power output of the car. Overall the drivetrain is a uniquely independent part of the car which was developed to provide a max power of 32 kW, and transmit 80 N-m of torque to the wheels, providing a quick acceleration and ability to adapt to longer endurance type races. The system is composed of the following major parts:

1. Drivetrain package ○ Emrax 208 motor ○ VW Jetta rear wheel hub bearing support ○ Lafayette Flex Hub (L. Foulk 2021)○ Lafayette Motor Spacers (L. Foulk 2021)○ Lafayette Torque Triangle/Motor Shaft coupling (L. Foulk 2021)○ Lafayette Drivetrain Housing (L. Foulk 2021)○ Mcmaster 62375K141 Quick Disconnect Sprocket - Front (L. Foulk 2021)○ Mcmaster 2299K58 Sprocket - Rear (L. Foulk 2021)○ Mcmaster 5905K338 Needle Roller Bearings - Differential (L. Foulk 2021)

○ Grainger 28408TC Dual Lip Rotary Shaft Seal - Differential (L. Foulk 2021)○ RAVENOL J1C1109 SAE 75W-90 Gear Oil - Differential (L. Foulk 2021)○ RCV Performance tripod housings - Differential (L. Foulk 2021)○ Drexler 140 mm Limited Slip differential○ Eccentric chain tensioner rings ○ Rear Sprocket Hub Adapter - Aluminum○ ANSI 50 Chain

2. Half shafts ○ Spline Half Shafts ○ Tripod Roller Bearings ○ RCV Performance Tripod Rubber Boots ○ Wheel Hub Rubber Boots○ Half Shaft Spring loaded end buffers

The top level diagram is shown below with an exploded view to see each component..

Figure 1 - Drivetrain system diagram

Current State of DesignThe current state of the drivetrain is as follows:

The drivetrain components pictured above have all been manufactured and assembled, wth necessary bugs worked out. Upon completed assembly, the team needed to then connect the drivetrain package above to the wheel of the car. This involves the half shaft list of components mentioned in the introduction. Not pictured above are the RCV performance tripod housings which slip into the differential and accept the spring loaded end of the half shaft. These parts were ordered in the spring of 2021 and assembled on the drivetrain package (Figure 2.) Unfortunately, the team ran out of time to assemble the half shafts and connect the drivetrain to the wheels. The 2021-2022 team will need to source one Nylon Half shaft spring loaded buffer, and correct length half shafts. All other drivetrain components are listed on the BOM and in the shop in an appropriately labeled box “Drivetrain Parts 2020-2021 L. Foulk”.

Figure 2 - Drivetrain system assembled - iso view

Figure 3 - Drivetrain system assembled - top view

Drivetrain System Installation Guide How to Install

Installation of the drivetrain into the car is made relatively easy with the above design. In order to install the system into the car use 4, ⅜-16-2 Lg. hex head bolts and reciprocal nylock nuts. Have someone, potentially two people due to the weight of the system hold the drivetrain in the rear envelope of the car. Attempt to align the mounting tabs welded to this rear envelope with the top and bottom two holes on the housing of brackets of the drivetrain. Once aligned, fasten to the car via the aforementioned bolts. Torque to a minimum of 25 ft-lbs. Once The main body of the drivetrain is in place, tension the chain using the eccentric chain tensioning rings. Finally, install half shafts into differential and wheel hub housings. Ensure bearings and rubber boots are packed with grease prior to final installation.

Assembly/DisassemblyDue to the complexity of the drivetrain system A disassembly procedure will need to be spec’d. It

is as follows: 1. Remove 2 (One each side) - M8x1.25x13mm Lg Socket head Cap Screws from inside of tripod

housing cups using an extra long M6 allen wrench. 2. Remove 2 (One each side) - Dual Lip spring rotary seals from the differential using a small flat

head screwdriver. 3. Cut lockwire on rear sprocket and remove. Remove 6, ¼x20x1.5 socket head cap screws. Using a

gear puller (From rob) or a dead blow hammer, remove the large rear sprocket. 4. On the motor connection side. Remove 4, 1/4x20x1-¼ socket head cap screws on the rear

eccentric ring tensioner. 5. Remove 6, 1/4x20x1-¼ socket head cap screws on the differential to eccentric ring tensioner

plate. 6. Remove the eccentric tensioner and set aside. 7. Remove 4 bolts holding the motor in place. 8. Remove the motor side drivetrain housing plate (0.5 thk aluminum). 9. On the sprocket side, remove the quick disconnect sprocket set screw and loosen the 3 bolts using

a 7/17 socket. Upon doing this because of the taper, the sprocket will release and you should be able to remove the quick disconnect hub, key and sprocket.

10. Next remove the 5, 3/8x16x3/4 Lg Hex head bolts holding the VW Jetta Rear wheel hub on. 11. Using two ½ open end wrenches, disconnect the 3 bolts connecting the flex hub to the torque

triangle/motor shaft combination. 12. Using an M6 allen wrench remove 3 bolts connecting flex hub to motor. 13. Now, remove the set screw in the rear sprocket hub. 14. Remove 6, 1/4x20x1-¼ socket head cap screws on the differential to eccentric ring tensioner

plate. 15. Finally, disconnect the drexler differential, eccentric tensioner ring and sprocket side differential

housing plate. 16. Repeat this in reverseorder to reassemble the drivetrain package.

Future Team RecommendationsThe 2020-2021 FSAE team has the following recommendations for next year's team. Firstly, the

correct length half shafts were not sourced. The drivetrain will need to be mounted into the car and existing half shafts will need to be modified to fit with proper tolerancing and/or new half shafts will need to be ordered. Secondly, the needle roller bearings for the differential which support the tripod housing shafts have a bit more play than the team would have liked. This phenomenon should be investigated by next year's team prior to full scale testing of the assembled car.

Also, the motor has a very specific specification requiring the motor bolts to be 16-16.8 mm into the motor. Due to the spacers and flex hub, this length of engagement should be verified by multiple people so as to ensure the bolts do not ruin the motor, or pull out during operation, both of which would be catastrophic. Ensure that all of the fasteners are sufficiently torqued, and are rules compliant. Typically this requires them to all have nylock nuts or be lockwired. They also should be of the strongest available variety. The differential was not filled with fluid, and thus this must be done prior to in car testing of the drivetrain. Also ensure that the tripod rubber boots and tripod roller bearings are packed with grease prior to testing.

The current gear ratio of the drivetrain is approximately 3-1. This was calculated with a rudimentary MATLAB script. It was intended to use new data from dyno testing to develop a function for the torque output of the motor. Other considerations that were not added and could potentially be, are the addition of a turning analysis with shifting car weight, different friction throughout the entire car, efficiency calculations based on the battery potential, as well as an analysis of the car going around the track. This was not developed any further than predicting the gear ratio simply because the 2020-2021 team did not get any dyno data before the end of the semester. This script should be built upon and provide a solid analysis as to the gear ratio and drivetrain choices going forward.