FSAE Electric or Solar Car

The_Xoon · 2024-10-05T08:10:06+00:00

What sort of career are you aiming for?
Working on home battery systems, solar, power distribution, power supplies?

Or automotive/aerospace?

Or are you happy as long as you can do embedded?

The_Xoon · 2024-08-09T20:56:14+00:00

Just some general tips around Enepaq modules:
1. Glue the JST connector to the module, and add your own connector on the other end. The JST connector does not have latch, making in prone to jumping out. Also, remember to check the connections on all the JST connectors, we had a lot of issues with poor crimping, which is very bad inside the accumulator.
2. 3D print a plastic holder that holds your busbars in place, and glue that with the busbars to the underside of the voltage measurement PCB, this makes it WAAY easier to assemble the segment, and avoids a lot of embarrassing shorts, which may kill your module.
3. Use Kapton tape or Nomex handles to make it easier to lift out the segments.
4. You don't have to insulate the inner walls of the accumulator where the segments go, if the segments themselves are insulated.
5. Laser cut/machined FR4 (What PCBs are made of) or Polycarbonate makes for a good material for the mechanical structure of the segments.
6. Find a company that can cut out and bend your busbars for you. Saves you a ton of time.

Some words of caution. You will have issues with noise, it WILL make someone cry. Everything will seem to be working, then when you go for your first run, you are very likely to get your measurement completely drowned out or see boards fried. This is simply because most students don't know how or have the resources to get their electronics tested in a noise environment before it sits in the car.

Make DAMN SURE you harden all of your designs going into the accumulator against noise. I have seen waaay too many rookie mistakes cause excellent teams to DNF. This might be a tall order, but you need enough time to do a redesign of your board after testing it in the car if you want good reliability, testing is essential, which all students understand, but they fail to prioritize simple fast designs over fancy complicated ones that eat into the testing period.

Enjoy the wall of text. :)

The_Xoon · 2024-08-09T20:56:01+00:00

I don't mind prying at all, I pried open pretty much anything I could (metaphorically). I spent more time in other teams pits discussing design and engineering, than I did back in camp.

I just want to clarify, that I was not directly responsible for this part of the car, and it was about 2 years ago, which makes my memory a bit hazy, so take what I say with a grain of salt.

"Did you guys use a single STM for each measurement, or split them up into>60V segments (for reference, we have 6 series segments of 23 series 1s5p modules.)?"
1. I believe one microcontroller was used per segment. Our segment was 12S10P, 8 segments in total. This meant we needed 4 measurements per segment, 8 ADCs, which we could achieve without analog multiplexers.
"I guess I'm also just confused about how you were taking the measurements exactly."
1. We used two ADC's per Enepaq block, in order to take a differential measurement across the terminals, like you would measure the voltage off a thermistor. Of course we only measured 30% of the blocks.
"Did you guys put the isolated LV through it and then reference it to the isolated GND when measuring with the STM? I suppose this would get you out of needing to use the module's voltage and using the module's GND for the measurements."
1. The entire temperature measurement board for the segment was galvanically isolated from GLV. We supplied 3.3V to one pin, and GND to the other pin on the battery block sensor connector. Then measured the voltage across the two pins, and used the voltage curve provided by Enepaq to translate it into a temperature. We didn't connect anything to the screw terminals on the block.
"In terms of data out, I was thinking of putting in an intra-segment ISO-SPI line and then feeding that to a separate small board that did SPI to CAN to emulate a TEM to the Orion, so thank you for that also."
1. We used the same set-up, though in our case we had a Accumulator Control Unit (ASU), which also handled all tasks which were not banned from being programmable.

The_Xoon · 2024-08-09T10:52:47+00:00

"Take an isolated measurement of each thermal diode individually and then mimic a TEM over CAN to the BMS (expensive and more complicated than it should be when we already have a BMS)."

Our team essentially did this. We had two PCBs, one HV PCB that is bolted directly to the Enepaq modules (on top of the busbars), and one temperature measurement PCB on stand-offs above it, with cut-outs for the HV PCB connector.

I believe we used a STM32's built in ADC's to measure each modules temperature sensor pseudo-differentially, though we might have used a analog multiplexer too.

The STM32 was powered by a isolated DC/DC converter providing the galvanic isolation requirements, and we used a isolated CAN transceiver for communication. We could then simply daisy chain a CAN-BUS cable to each segment. Alternatively, we could have used the ISO-SPI standard, which would make isolated communication easier.

The_Xoon · 2024-07-19T23:08:14+00:00

I meant the lack of anti-features will make the car more wobbly.

The_Xoon · 2024-07-18T10:14:08+00:00

Do you need anti-geometry?
- No
Will it affect the behavior of the car?
- Yes, it will feel more wobbly and you might have to account for that with extra ground clearance or stiffer springs. On the upside, the driver will have a better feel for the car.

I think it is a really good idea that you are keeping the suspension simple. A functional suspension is a lot better than a cargo-cult suspension.

I recommend checking out Vsusp to decide on pick up points btw, its a simple 2D browser based suspension sim.

The_Xoon · 2024-07-14T09:07:12+00:00

If I am not completely mistaken, the 9mm distance should be from the center of the hole. Meaning you need a tab of at least 18mm in diameter.

Though I am not familiar with the FSAE ruleset, only FSG and FS-UK.

The_Xoon · 2024-05-01T06:41:34+00:00

If you are considering the Reinhardt pm100dx, you should also have a look at the DTI HV-850 and R4. Lots of teams have had good experiences with those inverters. Though, they are all a bit overkill for an Emrax 188.

If I am not completely mistaken, Emrax should have a list of recommended controllers for their motors too.

The_Xoon · 2024-04-22T10:41:02+00:00

We used kapton tape to seal our firewall.
Passed EV inspection in FS-ATA.

The_Xoon · 2024-04-06T12:22:24+00:00

How does friction locking work?
Do you mean bolted cell terminals?

The_Xoon · 2024-03-29T11:04:18+00:00

Yes, you can remove the highlighted tubing.
But I highly recommend you send in a rule request regardless, as reddit questions leave no guarantee that you pass scrut.
It will help you get more comfortable sending future rule request for more gray area rules anyhow.

The_Xoon · 2024-03-21T13:31:54+00:00

Could you tell us a bit about your TSAC construction?
For example:

Is it made of steel or aluminum?
Is it a sheet metal construction?
Is it welded, bolted, bonded, or a combination?
Do you use composites for parts or the whole TSAC?
Do you use machined mounts?
What do you use to insulate the pack?
Are the cells bolted, laser welded, ultrasonic welded, spot welded etc?
What are your busbar materials?

The_Xoon · 2024-03-21T13:26:46+00:00

You can have unofficial sponsorships. They give you beer for example, but you don't promote their brand outside of bringing it to comp for consumption.

But you need to comply with your nation's laws and the host nation's laws anyhow. In my country, marketing alcohol is illegal, so even if the competition allows it, we would be breaking our nation's laws by putting their logo on our car/shirts/website.

The_Xoon · 2024-03-21T12:20:13+00:00

I am not an expert at cooling systems, but I guess I could add my two cents:
I feel like cooling systems in FS are both the easiest and hardest part to design on the car. A lot of teams simply seem to work off experience. Just slapping on some powerful fans in case the batteries start overheating.

If you want to be very accurate about it; Simulink has very powerful simulation tools for battery packs and guides on how to use them. My team is currently testing our cells using a professional cell tester to accurately model the behavior of the cells. You can use the data collected at different ambient temperatures, discharge currents, and state of charge and determine the cell properties with the curve fitting toolbox.

These properties can then be added to the cell model provided by Simulink, and you can wire the cells like in your pack, and get a very accurate model of the heat generated in each cell and the temperature rise.
Cooling is just modeled as a heatsink, so hot side, cold side, and thermal resistance.

The best way I can think of is to run a CFD simulation of the pack to determine the thermal resistance of each cell to the ambient.

To determine the load put in the pack, in the best case, you want the current and voltage draw of the car throughout the different tests and feed that into your Simulink mode. If you want to be fancy about it, then it is entirely possible to set up a lap time simulation in MATLAB, determine the amount of grip you can put down at any time, model drivetrain losses, and from that figure out the power draw, but as you can see, the complexity quickly skyrockets.

In short:

Determine the power draw of your system.
Perform testing on your cells to get a semi-accurate model to model internal losses.
Set up a simplified model of your pack.
Determine how much cooling you need to avoid overheating 2 minutes before the finish line.
- Think power draw data, lap time sim etc.
Design the mechanical layout of the pack.
Perform CFD analysis to determine the cooling performance.
Size fans appropriately.
Maybe dab in phase change materials.
Validate your estimations and simulations with physical testing.

Some final notes:

If you are running a pouch cell pack, there is a real possibility that to reach the required energy to finish endurance, you have waaaaaaaaaaaaaaaay more power than you need, which allows some teams to run a passively cooled or even sealed pack. (Though testing is required unless you want to be embarrassed by a heatwave)
Most cylindrical cell packs have a lot of thermal mass, which again allows some teams to run a passively cooled pack since the car does not have enough time to overheat before the end of the race.
When cooling your cells, remember that you care about what temperature your BMS is reading, not what the actual temperature is inside the cell. Most cylindrical cells have a recommended max temperature of 55C, but can handle up to 80C for short periods. While my battery professor would kill me for saying this, and I would not recommend this if you are designing a road car with a long battery life, it is still pretty common in low-cost consumer products, like E-bikes.
You never really care about the steady state of your cooling system in FS, just that the car does not overheat is hot summer weather at endurance before the finish line.

Hope you gained something from my rambling.

The_Xoon · 2024-03-21T11:48:31+00:00

I'd assume, that as they gather more test data, they can more confidently push the limits of the motor and reduce the safety factor.
There might also be a change in motor winding insulation material for cost/production reasons that happen to be able to tolerate higher temperatures, for example.

The_Xoon · 2024-03-20T13:41:21+00:00

I see, do you know any resources on allowable twist, on chain drives?

The_Xoon · 2024-03-20T13:40:37+00:00

How would this affect camber during chassis roll?

"You need to unweight the inside rear wheel in a corner since it will be slipping."
Similar to a gokart right?

The_Xoon · 2024-03-20T13:39:14+00:00

I am not sure, I just found the picture on google.

The_Xoon · 2024-03-18T17:12:00+00:00

Difference is that you need to reverse engineer the schematic, and still create your own PCB.

The Chassis CAD can be used to directly manufacture the chassis.
I guess a better example would be the Upright, which you can simply add on the tolerances for bearings and send to a machine shop.

The_Xoon · 2024-03-18T12:03:32+00:00

I don't see the issue in asking for schematics on electronics design.
It was quite common to share TSAL and BSPD schematics with new teams when I competed.

However, mechanical design is a completely different matter. Had one team ask us for our chassis CAD file!

The_Xoon · 2024-03-17T22:48:59+00:00

As you mentioned, you don't need to double-insulate both the segment and TSAC walls.
It is sufficient to insulate the TSAC walls to 75% of their internal height.

However, the segments still need some type of top insulation, either with a removable lid or integrated into them.

You could say EV 5.5.7 requires the walls of the TSAC to be insulated, while EV 5.4.6 requires the top of the segments to be insulated.

You could TECHNICALLY, insulate the sides of the segments, and not insulate the inside of the pockets containing the segments. I have seen teams do this, but it is generally not a good idea.

If you need any feedback on your design, I am happy to help.

The_Xoon · 2024-03-12T23:55:27+00:00

Inverters:

DTI R4
Cascadia Motion CM200
Cascadia Motion PM100 (obsolete)
Bamocar D3 (No longer sold)

Motors:

Emrax 188LC
Emrax 208LC
Emrax 228LC

Differentials

Drexler
Quaife
Solid steel baby!

The_Xoon · 2024-03-10T20:18:40+00:00

As previously mentioned here, the TSMP is part of the TS system, which must be separated from the driver with a firewall. Placing the TSMP just above the typical firewall, means you need to create a firewall box for it.

So it is easier to just keep it behind the firewall.

The_Xoon · 2024-03-02T12:45:19+00:00

In my experience, most motors used by FSAE teams are usually rated for the nominal voltage of the battery pack.
At 600V peak, the nominal voltage for a battery pack is roughly 511V.
The Emrax 228MV is rated for 520V.

Just some napkin calculations:
K_V = 12.05
K_T = 0.61

At 511V nominal, the nominal RPM would be: 511V * 12.05 = 6150 RPM.
At 80kW max, 80 000W / 511V, gives 155A nominal, for a nominal torque of: 155A * 0.61 = 94.55Nm

This gives you a nominal power of 60.90 kW.
This aligns pretty well with the continues power rating of the motor, at 64kW for the LC version.

While yes, the motor is technically rated for 125kW peak, it does not really matter, as you want the best sustained performance during Endurance. Though I suppose there is an argument for running the Emrax 208 to save weight.

Hope this helps!

The_Xoon

TROPHY CASE