Mechanical Meeting with MIT
Body Team
- What paint do you use to paint the car?
- How did you guys go about designing your shell to shell attachment mechanism?
- In general, something quick to attach/detatch
- leaving small gaps - enough to tape over
- Any insight on how to do large-format resin infusion? Do you do yours in house?
- Own layups using prepreg
- Prepreg hard to source
- Kentucky may use wet layups for the whole shell
- Own layups using prepreg
- How do you attach your bulkheads to your car?
- MIT has no bulkheads
- MIT has no bulkheads
- what mold release do you use?
- frekote
- peel ply
- foam → fiberglass tooling → frekote, shell
- Array Attachment
- VHB Tape between array and composite shell
Dynamics
- Frame
How do you simulate your frame?Solid bodies/Shells?If solids, do you use beams to establish displacement BCs or do you just simulate with load cases
Experience doing a space frame or is all frame sim on composites?
- Suspension
- How do you train your members to have a good knowledge and intuition of kinematics, especially freshmen who haven't taken dynamics yet
- 1st month is just developing skills
- Statics FBD,CAD, Assembly, FEA,
- New members get a subteam project
- Brakes makes a calculation spreadsheet off of a FBD
- Lot of shadowing upperclassmen
- Freshmen usually don't design anything on their own
- Take in a lot of sophomores
- No rigid curriculum
- If there are less upperclassmen, focus more on education
- Recruiting
- Open to anyone who's interested in joining
- let people self select
- no goal/application
- what resources do yall use to better understand susp technical concepts
- How do you train your members to have a good knowledge and intuition of kinematics, especially freshmen who haven't taken dynamics yet
- UNSPRUNG MASS
- How do you design parts that can withstand fatigue? Hand calcs? FEA? Want to design for ASC not just FSGP
- FEA internal SF higher than regs
- Instron testing of all welds/composites
- Spare parts
- Precedent on old parts
- No specific calculations
- Do you use topology optimization for lightning or do you do it by hand/trial and error?
- Only brake rotors
- Start with base design, run FEA
- Would rather have testing time rather than design optimization
- Do you use the Mitsuba motor? What do you aim for in your tires
- what tires do you use?
- Bridgestone
- Source first since they take a while
- 200kg with
- what tires do you use?
- Do you use 2 motors
- Direct drive
- 2 on Gemini (MOV)
- 1 on their (SOV)
- How do you design parts that can withstand fatigue? Hand calcs? FEA? Want to design for ASC not just FSGP
- Steering
- How do you control toe on your rear wheels?
- double wishbone on front
- modified L arm on the back
- How do you control toe on your rear wheels?
- What is your upper level design process/design philosophy?
- Start by deciding steering system that you want to use
- noralyl will compartmentalize and then ensure that each part of the system integrates onto the upright
- look for where steering can best attach to the upright first
- steering angle chosen early on
- Nimbus
- acrmin but not
- Gemini
- achermin full on
- Make sure things are overconstarining your system and then making sure that the system no break
- what kind of testing/validation do yall do?
- To what level do you model and characterize your car?
- What components do you characterize(ie. shock absorber characteristics)
- what data do you collect from onboard sensors
- how do yall set up ur tests,
- what are the inputs/outputs
- Speed of Car
- Temp of battery
- TMPS
- Lux measurement
- (no IMUs just talked about it)
- what have u learned abt how to do a test correctly/efficiently?
- how do u calculate uncertainty in the sensors (if at all)
- Senor uncertainty isn't really kept into account
- good enough sensors should be close enough that you probably arent worried about it propagating out
- How do you decide what data should be sent over telemetry during/after driving?
- Strat team will take input from the car telemetry and a scout car that takes info at the front and then they spit out target range of speed and then stick to it
- How do you choose what sensors to use?
- Hall for battery 40A onboard (on PCB)
- What is your transmission range?
- Range for transmission
- How did you decide on the placement of the radios/antennae (if applicable)?
- Do you do any analysis to predict the amount of noise generated by different arrangements?
- How do you store your telemetry data?
- How is the data incorporated into your workflow?
- To what level do you model and characterize your car?
Power Generation
- Do you use commercial MPPTs, if so which ones?
- Port in from 170v mppt 3 of them
- Battery 115V
- Old car used drive tech MPPTs but they don't produce them anymore
- https://www.tpee.nl/home/products/
- Port in from 170v mppt 3 of them
- Which solar cells do you use, do you manufacture the panels in-house or buy them completed?
- Buy maxeon gen3 & gen7
- Direct contact with maxeon Elizabeth Chong
- Start early
- gen7s are only for solar cars?
- have to get them approved by fsgp/asc, not yet on the approved list but hasn't updated since 2021
- encapsulated outsourced
- SunCat
- Didn't use this year due to time one and coms issue
- Mito Solar( Netherlands)
- Known for doing wsc teams solar cells
- super cool
- module layout 9 5x4, 8 4x4, 14 individual
- In series, bypass diode every 4 cells
- Buy maxeon gen3 & gen7
- How do you mount your modules/array to the top shell?
- Shell attachment process
- Layout with tape
- vhb tape on back surface of modules
- epoxy edges
- Prevent shorting to the shell
- silicone to plug holes around wires
- good pete coating
- Plastic on the back, capton tape to insulate from shell
- Paint
- Outsourced - can check for us
- weather resistant
- Outsourced - can check for us
- Shell attachment process
- Do you have a Power Generation team? And if so, what is the scope of their work?
- don't think so, array/battery team
From Matthew: (Only if MIT makes them in house)What's your typical PPE and SOP for working with the array & HV electronicsDoes MIT faculty and admin aid the org (IE with facilities/labs etc)What is target mppt power density and cost?How do you feel about pcb magnetics (inductors, transformers)Mcu family of choice? What rtos if any? How developed is your sw stack?What is passive power consumption of the MPPT?Is mppt running off power from array or vehicle bus (12v, 48v)High voltage low current or high current low voltage?Are you madlads and just go ac with string inverters instead of mppts
Notes
- Composites with Instron testing
- Find internal resistance of battery, finds power output. does CFD, cutouts are on the side near the wheel wells
- Battery box is made out of 2 layers of kevlar and then foam core, this time using nomex core
- Putting it together they epoxy the panels together, do a wet layup
- MPPTs they are housing in acrylic or polycarb
Next Gen
Body
- How do you attach the array to the shell of the car?
Dynamics
- Frame
- thoughts on a 3-layer space frame or a space frame catamaran?
- Suspension
- What software do you use to design the suspension geometry? VSUSP? Lotus? Own kinematics software/calculator?
- What suspension properties do you optimize for? (how would u if ZERO prevdata) what were the main design factors? (i think spring rates, roll, pitch, bump str, hardpoint sensitivity, CG bias)
- IMPORTANT what weights did yall end up assigning to each major factor and can u give a quick rundown of why
- what is the very first thing u did when u began design? what is the second thing u did?
^ again but if u didn't have a previous car to work off of (zero data) - how did u do top op? (what tool, is it straightforward or anything gotta watch out for)
- did yall use lapsim? if so what inputs/outputs did u use?
- What did u use besides spring/damper rate & tire compliance to calculate effective spring rate?
- how did u do the math on most of these things? Make ur own excel calculators?
- Unsprung
- How do you go about preventing uprights from being excessively large? How do you decide the shape of your uprights?
- Do you use metal 3D printing?
- Steering
- How do you approach steering optimization?
- Do you have a program that calculates steering metrics? what metrics go in and out?
- Do you take tire slip angle into account for the optimization? if so, where do you get your tire performance data?
- How closely does your steering team work with suspension to handle things like steering wheel torque as a relationship between scrub radius/mechanical advantage of steering wheel?
- How do you decide lock to lock steering wheel angle?
- have you ever experimented with alternate steering designs(not a tierod based 3 bar mechanism)
- How do you approach steering optimization?
Electro-Mechanical
- How do you assemble your battery box to keep it electrically issolated?
- Do you cool your batter box? If so how did you go about calculating the necessary air flow?
- hand calcs, see Jacob Yan message i cooling
- How do you split up all of your electrical enclosures within your car? Like do you have an enclosure of high voltage lines and low voltage lines?
- most PCBs uncovered
- What materials do you use to make your battery box and other enclosures?
- Same as us
Ergo
- How do you calculate/verify that your brakes can actually stop the car?
- What do you do, if anything to keep the driver cool?
- what specific materials did you make the pedal box out of (pedal base, any mounting points/holes, arms)?
Data Acq
- Data to collect
- State of charge
- Speed
- Battery Temperature
- TPMS
- Uncertainty?
- Know uncertainty/characteristics from experince with he sensor
- Excercise human judgement
- Data to share real time
- not sure but can ask their data acq
- Also collect data from a scout car
- How to choose sensors
- Battery - hald()halt? sensors
- on pcb/off pcb
- Battery - hald()halt? sensors
- sometimes an issue to get data to the pits at FSGP, have a large antenna, can find range
- antenna by driver so signal escapes out of windshield
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