2019-11-30 Design Review Meeting with Nate
- Micah Black
Nate - Senior Hardware designer at Nuvation, PM for MSX
- Has used Elcon chargers before
- MSX used the SMC100s as a backup motor, they had it working.
- TI has support engineers, for reference boards, etc - SDC contacts - TI reps are assigned geographically.
Present: Aashmika, Micah Bai, Arshan, Josh, Micah Black, James, Jenny, Chen, Lauren, Jessica, Darby
Aashmika went through general car overview of the electrical system
MSX BMS:
Go/No Go for battery parameters
ADI8280 over SPI for voltage/temperature
MSIX used a purely logic system for the BMS
Scrutineering just needs to see contactors open for 3 conditions
Steering
Critical buttons should not be on screens, they should all be physical buttons
Tablets for a screen, Pi creates a wireless connection that the tablets connect to. You have a whole app ecosystem to use. Kiosk (lock down the tablets) app that would navigate to a webserver hosted on the Pi. With the webserver, we can connect to it with our laptops when debugging the car as well. Just let the tablet run a native android OS. Open ports for specific devices to access.
Double sided foam tape on the tablet, attach it from the back side of the opening, and it looks like you are not really using a tablet.
For telemetry - wireless CAN bridge over the 400MHz? band - is transparent to the network - cream colored project boxes should be somewhere.
MSX used 3 different CAN buses - TI part that had 3 CAN buses, and aggregate the data.
-Telemetry
-Battery
-Control
Strategy timesaving - should be able to drive without the Pis booting up - get away from pitstops quick.
Short distance wireless communications should work well within the car.
The steering wheel gets abused the most. Make the steering board robust. Discrete buttons with the fly-wire to the board. Prevent the button from being over-pressed.
Power Distribution
LTC4417 Power Path Priority
A lot going on in this board.
For previous versions there was CAN and power over the same wire, so some questions about the CAN hub.
RGBW serial lights that can go different colors. MSX used the flash LEDs from blackberry. Kapton tape for the Amber lights.
Motor Controller
MSXII Precharge was hardware based.
Conformal coatings
Silicones based conformal coating comes up as a strip - toluene can caused hearing issues - use a fume hood.
Bi-Metal strips for the thermostats - can be used as an upper bound for voltage monitoring.
Available in 5 degree increments
Lights Boards
Thermal Vias - Usually spaced as close as possible, and as small as possible.
Heatsinking to something must be able to radiate the heat as well.
Aux Charger
Rules used to be primary cell Aux.
If someone wants to take this on, then this is a great project to do.
Keep one-upping the scrutineers for regulations
Solar Sense
What is the issue?
Yellow construction work lights for testing the panels
Spool of wire for loads,
Raceware Tech - MPPTs that were programmed for settings.
Robustness - They'll fail and the no one will no how to fix them.
DC-DC Modules
Vicor modules have the switching logic inside, but the components outside.
Solving the heating problem - bigger package - larger heatsink - bigger fan.
Thermistor switch for controlling the fan.
Management Input Perspective
Break in to teams to work on projects - mentor relationship
If not working on the board, probably not ideal to bring up the board - usually ends up in more broken boards.
Battery
MSX did battery testing - capacity - great job for co-ops
Why did this knowledge not get transferred to MSXIV
Lithium at low voltage is not dangerous??
Firmware
See Arshan's firmware overview presentation
Measuring MPPT currents - measure battery current, measure load - Solar is the difference
Undervoltage fault - current directional fault - disable fault while charging
Killswitch - Regening on to a bus, but you lose the load - voltage spike - the killswitch should be wired through the motoro controller relays as well.
BPS Strobe - Through the power distribution rear board
How do we check our battery states - can we see them when powered on the AUX?
Have a timer on the current direction (30 seconds) - prevent misuse (driving it beyond low)
Driver is not going to interact with the Idle state
Write a user manual
Nate knows about the relay hysteresis issues - seems like a common problem.
DC-DC Overtemp
In any states, the fault goes to an emergency - take action based on where you came from.
If you aren't able to close the contactor - there is no reason to do precharge - do we still want firmware control?
Time sequence delay for heartbeats - make sure its within the acceptable range.
MSX was taken to FSGP 9 with code that Nate wrote ("scary because I'm not a coder")
-Arshan should be thinking about the state diagrams, etc, CAN communications, GPIO driver, CUBE implementation, etc
-Code written by others should work at a black box level to what a lead defines.
-Start at the high level, eat the dots going to the lower levels
-Complete your task before I do.
-Do the architecture RIGHT. Give yourself the time for this. If this is wrong, then any code written will also be WRONG.
-CAN Message Maps
-State transitions, etc
-What to do when in a state if you don't want to be there
-Do you need state __?
-High level testing can be done on Linux, mock out the drivers, etc. HIL testing - make sure it is working on a controller board as well - use a Pi to provide any inputs necessary.
-Backend database for logs on the Pis
-Lift the wheels off the ground and do all the remote control testing
-Interior mirrors that go out through the windows
Driver Selection
A driver that drives the car like a car is best.
They picked drivers from the PAC area, and tested how well they respond to commands, stay cool, etc. - Drive around ring road, tell the driver to speed up and slow down continuously until the driver tells them to stop. You can get some driver ergonomics testing this way as well.
The best driver will be one that drives it like a car but also knows everything about what is going on inside it. If you don't drive it like a car, then you will be much less efficient, slower, etc.
Anything that people will be interacting with should be designed for robustness.
MSX had issues with brake testing, had to reduce tire pressure as well.
Other comments in the bay:
-at FSGP 2009, Midnight Sun did a barrel roll, landing on its tires. MSX got the "I want to be an airplane" award.
-Rotor locked up and driver said there was smoke but couldn't identify where it was coming from. Keep
-Battery Undervoltage protection - the undervoltage condition on lithium batteries is not too big of an issue. You have less energy stored and thus a less violent explosion, usually just a small swelling and a puff. It is really the overvoltage that is an issue because then you are generating heat and have a ton more energy stored that will cause violent explosions.
Inside the cells, the crystal will get larger, dendrites will form, the pressure will build, and the cathode and anode will be squished together, creating an internal short circuit.
Motor tuning - the motors should be electrically silent when running. If there is noise, they are not tuned correctly. The Tritium software gets its tuning values from the motor itself, so it has to be connected, you can't just type in configuration values. To get better efficiency (at the cost of some torque) you can hold the motor absolutely still so that when measuring the inductance in the
All grids are just one big control loop - this is where Nuvation can compete on some super cool projects.
There was some multiplier on our score for MSXII 0.83% (or something like that) that was dragging our score down - what was this? This is the car to break the "E5 curse".
At competition, everyone is on the same team. We are here to prove that solar powered transportation is possible. The best race is one where everyone finishes
As an alum, he is not really seen as a threat, so teams will be more open about strategy, etc. Michigan's strategy is not to have the best and most reliable car. It is to be able to swap parts in and out super quickly. They spend the last year before comp getting their team running like a well oiled machine.
MSX was ready in February, and was testing as soon as the snow melted.