Dan Bohachick / BPS inspector, race strategy

If you organize a 1-on-1 with this person, then fill in the timeslot and your name in the table below.

Question 1: Pitfalls for strategy and off-network considerations

• Time constraints? Answers this with an explanation that route understanding is most important

  • Route book given (known), breakdown into elevations, road conditions, awareness of lanes (tight passing?), where cities/towns are

  • consider time limit, research routes and investigate likely areas of trouble, perhaps consideration of likely traffic constraints wherever they occur

• City segments? How to handle this?

  • Not a lot of time spent in cities/towns - past had East Coast routes so this problem was there - however in this case, try to get out of towns/cities and their traffic when you can

  • Consider when traffic lights may shift their logic if possible - ie., timing lights? Perhaps just check history of traffic on route roads in Maps depending on time of day - could we build this in

  • Would we be able to speed up to avoid these?

  • Assume some lost sunlight to shade in cities/towns?

  • Annotate route conditions by having the lead vehicle go ahead of time to check for road hazards and constructions and keep it on routebook

  • Some teams have tried to time lights (ahead of time), the best is to keep momentum - very hard to to do this, especially as city traffic networks usually change as the day goes on to handle expected conditions

  • Account and try to calculate the impacts of city segments, don’t be surprised

  • Best to have a very good idea of what the car is capable (extensive testing) - don’t force it beyond its capabilities, drivers will often get a feel for this as they draw – build Driver profiles seems to be an idea brought up by Menon in his presentation, and now again by Dan

    • Do not neglect how training drivers and having them be comfortable with the solar car is very important

Question 2: How to track time for average speed?

??? idk if the above question should be here or combined imma move on

Question 3: What considerations do we need for car dynamics beyond aero drag and rolling resistance?

• Pick a route, run it multiple times through different scenarios - without array, with array, different drivers

  • Vary route after you get a good feel of one type of terrain(s); try other ones

  • Aerodynamic drag for a given speed is important info

  • Attempt to identify impacts of different weather conditions (winds) - crosswinds etc on aero drag

    • Teams can get penalized for driving fast through strong winds

    • Good to set up telemetry to see these impacts in real time

  • Dan’s team would try to run the same circuit with different gaps, speeds, etc to test the motor’s efficiency and other tradeoffs in a constant road environment

  • Consider the most efficient speed - not always the best speed at the same time, it may be too low to be competitive for instance

  • Consider modelling individual driver style and driving energy draw profiles

    • Some are more capable with steering, braking control, etc.

• Understand what your array can produce in varying weather conditions

  • Getting current into battery can also have problems - ex he gives is that battery may have a hard time getting energy from solar at 90% since it’s more difficult to charge then

• As we are a cruiser class/MOV, our weight is very important

  • The array will be adding energy, however likely will never get an energy in = energy out as the Challengers do

  • Elevations and motor torque profile are very important

  • You may have power, but pushing speeds that you can’t maintain is hard

  • Consider penalty of charging - hard to model, but suboptimal situations will always occur

    • There is a strategic value and you need to be able to take in this kind of charge effectively without losing back

  • The most important part though is how the battery affects how you tackle terrain and elevations with your heavy weight and extra passengers

• Better to have the chase car to act as a HQ for strategy than the solar car, have a very good real time sync

  • Not mentioned, but this seems to be a call out for very good and reliable networking/telemetry

• Dan has heard of teams using MathWorks (MATLAB) to do simulations and vehicle modelling

• Clearly the takeaway through this Q&A is test test test!!!

Some good resources:

University subscriptions to IEEE, SAE - faculty have written papers on train/plane/car optimizations? Algorithms and approximations for different types of model

Question 4: Weather setup?

Did not get here

Q&A section for Micah

Question 1: Common pitfalls during scrutineering

• Testability of the board

  • Read through the test procedure

  • Do a mock scrutineering test

    • test points, harness, etc.

  • Overcurrent test, etc. Know the direction

  • Go through temperature thermistors to a setpoint - check charge and discharge value

• Behaves in the latching - must be able to see it

  • If you back down - cannot re-enable!

  • Latched until driver manually clears the fault

• Top shell at testing station

  • Maybe just have a visual indicator that you can wire it

• MOV battery packs

  • Make sure you can actually connect to them

    • Thermistor that you can actually connect

    • Long harnesses, etc.

    • PSU has alligator jumpers and banana lead.

• Come with DOCUMENTATION filled out

  • check scrutineering sheet

  • Testing current sensing

    • Verifying gain of A/D

• Connectorize it!

• Monitoring while away from shop

  • Make sure that none are under 2.5V

    • Might have grown some dendrites

Question 2: Custom BPS vs off the shelf

• Initially 75% used off the shelf BPS

• Now, most teams do custom now

Question 3: Counting cells

• Our modules are pretty compact

  • Loose cells

  • Modules and packing weight

  • Shouldn’t be an issue for us. Just bring an extra module

Question 4: Cooling

• Battery pack cooling - airflow impacted by many things

• Baffling and redirecting air to hot areas

• Environmental heat differences with air travelling through the pack

• Irradiance from the ground/array can induce heating into the pack

  • Insulate environment away from the pack

• 10 cells per thermistor is a good ratio

• Most problems come from not having a balanced module

Question 4: Long leads?

• Can cause issues with radio gear or main motor 3-phase wires

  • Might want to look into interference with radio gear

• Shielded cables

• Twist everything

  • cut down cross sectional area for radio noise

  • Lead length for passive/active balancing

• Per-module sub boards to do the measurements and communicate it back to a control board

• Would probably not recommend wireless for teams that are not an expert in it

  • Devices close together will introduce issues

• Connectivity - don’t disconnect certain cells in the series stack

• Just look at the way Tesla does it - not a bunch of extra monitoring

  • Flow temperature differences in cooling system

• Remove as much complexity / remove room for external signals to enter the system

• Minimize exposed wire coming off

  • Testability on boards can become a weakness

Question 4: Balancing?

• Generally spend the effort on a well-made pack

• Active balancing - activate with a plug-in system to use available power to rebalance things

  • But better for overall efficiency

  • Getting all states of charge - would have to monitor very carefully across all SoC

• Assumption - teams have not put many cycles into the pack

• Ripple through series stacks can cause isolation failures

  • Building their own DC-DC converters is hard to get right. If you’re doing it for all your modules

  • Loading or test equipment for simulations most teams do not have

    • Frequency response of the control loop - keying up radio next to it causes shorts

    • EMF and other noise sources to impact it

    • Gates - stray radio signals can turn them on

      • caps, zeners, proper driving circuitry short

    • Or make DC-DC modular enough to add on to sub-boards

    • Metal boxes would be good

Integration and getting the integration right - once that’s done you can worry about designing your own stuff.

Only a few teams have made power point trackers successfully.

Removable or settable fuses. At least have the built-in protection.

Start going back over designs and work on the ones that are beneficial to spend. A lot of it is just iteration.

“I think you guys have your stuff together”