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Mechanical Meeting with MIT

Mechanical Meeting with MIT

Feb 26, 2024

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

  • How do you attach your bulkheads to your car?

    • 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

  • 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 

    • Do you use 2 motors

      • Direct drive 

      • 2 on Gemini (MOV)

      • 1 on their (SOV)

  • Steering

    • How do you control toe on your rear wheels?

      • double wishbone on front

      • modified L arm on the back

  • 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?

Power Generation 

  • Do you use commercial MPPTs, if so which ones?

  • 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

  • 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

  • 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 electronics

    • If you're making your own converters, which topology? Llc resonant converters? What simulation work do you do? Any thoughts on adding an inverter stage and charging the car through a wall outlet

    • Does 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)

    • How do you feel about high voltage clearance and creepage

    • Anderson power poles or xt60s

    • 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

    • Anyone ever find that Tesla 48v wire harness guide? Cause I'm at Tesla and I can't lmao



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)

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

  • 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

Powergen

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