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Discussion Starter · #1 ·
Land vehicle Vehicle Car Ac cobra Sports car


Land vehicle Vehicle Car Formula libre Sports car


Vehicle Automotive exterior Auto part Car Machine


I'd like to present our Tesla powered Race Car project. The car utilizes a custom designed chassis, drivetrain from a Tesla P85, body from a classic 427 Cobra, and a battery pack from a Kia Soul EV.

I am a long time road racer (Sunbeam Tiger, Mustang GT1, Toyota MR2) in the PNW and have been wanting to build an electric race car for a while. However, up until now, the cost of doing this has been prohibitive. The availability of OEM EV components in the salvage yard has changed things.

This car is being collectively built by a group of friends who love the idea of doing something different. We have been working on the project for since December 2015, and are hoping to have the vehicle on track for testing this summer. We call ourselves "EPower Racing"

The motor is from a Model S P85 which is rated at 310 kW peak. However, we have no illusions that we will be able to run the motor at anything close to that for sustained periods due to overheating of the motor/inverter. We are putting in lots of extra cooling but only testing will tell if that helps. All reports we hear of from Tesla Track Days show Model S's going into power limiting within a couple of laps. For longer events, we will probably limit the maximu power to the motor to prevent heat build-up. Although we will have regen capabilities, we will most likely not use it the same reason. (Regen would also upset the brake balance as well which would be undesirable for a race car).

We realized very early on that the massive available torque and an open differential without the benefit of Tesla's traction control system was not a good combination. We worked closely with Jack Rickard/EVTV and Quaife Engineering to produce a custom torque biasing differential. These are now available from EVTV.

We chose the Kia Soul EV as the battery pack donor largely based on DOE test reports which showed it as one of the few OEM packs capable of putting out over 300kW for sustained length of time. It is also one of the lightest packs available. The 30 kw-hr pack (27 usable) only weighs 400 pounds. We purchase what was probably the first Kia Soul EV that was written off, and hauled it across North America! It was fully functional vehicle which allowed us to do some reverse engineering of the CAN bus. We are able to utilize the factory charger for both regular and ChaDeMo charging and obtain cell temperature and voltage data from the BMS. We will be limited in the duration of our runs due to the pack size, but we didn't want to double up on the pack before we even had any real world test data.

The chassis was designed in Solidworks including FEA optimization. The chassis with roll cage weigh about 220 pounds. VR3 engineering took our CAD files and CNC cut and bent all the tubes.

The suspension utilizes C5 Corvette spindles and hubs to keep costs down. However, since we were designing both the frame and A-arms, we were able to dial in exactly the geometry we needed using our SusProg3D suspension analysis program.

Total design weight of the vehicle with driver is 1800 pounds which, even with a torque limited motor, should give us a very good power to weight ratio.

The goal is to have the vehicle on the dyno early spring, then on track for testing in the summer.



https://www.youtube.com/watch?v=Ci8kHAb6iVw
 

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Fabulous build. IMHO you must use regen breaking to the max possible. Without your laps will be severely limited, I would expect this to give you perhaps 50% more laps. Depending on the track type, much less on a high speed oval. I do not see the brake balance being such an issue as it is in highbrid formula 1 cars as they fully charge their batteries I think. 4 wheeldrive would be a big benefit as it would give front wheel regen breaking.
 

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Discussion Starter · #5 ·
Our Tesla Cobra EV finally hit the race track in June and we have now run 3 races and a number of test sessions with it.

The performance has met our expectations and has surprised a lot of people!

As predicted, range, length of time to recharge, and battery/motor temperatures have been the issues. However, we did complete one 20 minute race at 180kW peak power setting and a second at 220kW. We have run the motor up to 300kW on the dyno, but it is unlikely we will ever be able to run at that level in a race. Qualifying sessions and time trials are a different story though!

Here's a link to some in-car footage:
https://www.youtube.com/watch?v=onPaceYswN4

Regenerative braking will help our range issues, but doesn't help with the temperature issues. It's a fine balancing act! We have tried running with various levels of regenerative braking but it makes the car hard to control at turn-in. In the one race we ran with regen on, I compensated by putting on some throttle at turn-in to disengage the regen braking.
(Tesla uses a throttle off/regen on strategy). In the future, we will try to implement a strategy to only use regen during straight line braking.
 

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The performance has met our expectations and has surprised a lot of people!
In reality you pissed them off.
ICEers hate being beat by electric cars.
Off the track, be very diplomatic, tread lightly and dont brag.
On track you will still be embarrassing them and they will eventually eek you out.
At least thats what happened down here (ELMOFO electric Radical)
Personalities might be different up there.

How many laps would you get on full power ? I think it would be at least twice as much as a Model S because of the weight.
 

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Discussion Starter · #8 ·
I think having a lighter car only helps with range if you run at the same power levels. Our pack is 27 kW-hrs. We are using all of that in 20 minutes - which is about 16 laps on a 1.4 mile road race course.
 

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I'm very interested in doing this to a vehicle myself for daily driving not racing. What controller is being used to run this thing? What is required from the tesla besides the rear drive unit which I see on ebay for $10k?
 

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Discussion Starter · #12 ·
Lessons Learned and Upgrades for 2018

We were extremely pleased with the 2017 debut of our Tesla Cobra EV car. It was quick right out of the box despite having to run at lower power levels. The issues we had were problems we anticipated: High motor temperatures, and insufficient battery pack capacity.

Battery Pack. The 27kWhr Kia Soul EV pack worked superbly, but was a little small. In order to run our 20 minute races, we had to drop our maximum power to 200kW or lower. Battery temperatures were high, but manageable. We added two high head centrifugal fans to our custom enclosure to help reduce the time required to cool the batteries between sessions. We are attempting to get hold of a 2018 Nissan Leaf 40kWhr pack for the new season. The pack is about the right size, the modules are easy to work with and can be re-arranged to fit into our available space, and the weight should not be much more than our Kia Soul pack (400 lbs). The cars will not be available for sale until Feb. 2018, but we have no doubt that we will be able to find a salvage vehicle within a month or two of release! If anybody can help with locating a pack, it would be much appreciated.

Motor Cooling. Stator temperatures would reach 150 degC in about 6-8 laps. To protect itself, the Tesla controller would cut back on the maximum power delivered. At the end of most races, we were down to about 150kW. The Tesla stator/rotor/power electronics are water cooled. Despite having a very high capacity cooling system and an ice reservoir, we were not able to keep the stator temperatures down. (There were no problems with inverter temperatures). This year, we will be experimenting with oil bath cooling of the stator/rotor air gap in addition to the water cooling. We will utilize a water/oil heat exchanger and a positive displacement gear pump to circulate ATF.
Regenerative Braking. With 60kW of regenerative braking, we were able to increase our range by 20%. Unfortunately, the car was very difficult to drive due to the huge rear braking bias. The Tesla controller puts regenerative braking on anytime the throttle is off – not good for corner entry. I think I spun the car more times than I have ever spun a car in my life! With a bigger battery pack for 2018 we should be able to get by without regenerative braking.

Charging. We utilized the 6.6kW factory Kia Soul charger last race season, but the long charge times (4.5 hours) quickly became an issue limiting us to the number of sessions we could run in a day. For 2018, we will be attempting to piggy-back off the work of the DIY community (Damien Maguire) and utilize two or three Tesla chargers in parallel for 20 or 30kW of charging capacity. We are working with the Sports Car Club of BC at our local track and hopefully will get a 150 amp service installed in the pits for 2018.
 

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Are you allowed to run AWD? I think running one of the small Tesla units up front would help you with a lot of your issues. You would have more balanced regen, there would also be power splitting, so each motor should get less hot to make the car go the same speed. For racing I wonder if some other non OEM battery solution would get you better results with less weight. The car companies lean the chemistry towards long life, ability to recharge at a fast rate and range. Generally you can get batteries that are lighter and have higher amperage ratings with the sacrifice of battery life, shouldn't be an issue in a car that will probably never see five figures on the odometer before the batteries get upgraded for the latest and greatest.
 

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Discussion Starter · #14 ·
If we were to build a 2nd generation car we would probably go with two of the smaller Tesla units (or even a pair of Nissan Leaf units) for the reasons you mention. However, this setup would also add a couple of hundred pounds to the car.

As far as batteries, going the salvage route significantly reduces the cost of the pack. In addition, there are not too many high performance cells actually available to the public. Pretty hard to beat the latest and greatest OEM offerings.
 

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It would add weight to the car yes, but wouldn't it allow a high enough increase of your current setpoints to offset that? Maybe it would be better on tracks with less turns since the extra weight probably reduces cornering capability.
 

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Motor Cooling.
Stator temperatures would reach 150 degC in about 6-8 laps.
...
The Tesla stator/rotor/power electronics are water cooled. Despite having a very high capacity cooling system and an ice reservoir, we were not able to keep the stator temperatures down.
That's an interesting challenge.

Do you have coolant temperatures at the inlet and outlet of the motor that you are willing to share?
 

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Discussion Starter · #18 ·
Yes, if the power we could put to the ground with an AWD setup were high enough, it would overcome any weight disadvantage.

Gaseous cooling is a possibility, but would actually be quite a bit heavier. The flow rates we would require would mean using some very large tanks. We already have the water cooling system which consists of a radiator and high flow electric pump (The ice box use is optional). The addition of the water/oil heat exchanger, gear pump, and lines will add less than 20 pounds.

Water temperatures are very cool. Here's a data point: Stator temp 171 degC, Inverter temp 43 degC, Water in 35 degC, Water Out 37 degC
 

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Water temperatures are very cool. Here's a data point: Stator temp 171 degC, Inverter temp 43 degC, Water in 35 degC, Water Out 37 degC
Thanks :)

With cooling water gaining only 2 °C in a pass through the motor, the coolant isn't being used very effectively. With the water outlet at 37°C and the stator at 171 °C, the flow of heat through the motor to the coolant is remarkable ineffective. I can see why running coolant through the stator-rotor gap is being considered, since the heat is not flowing effectively from the heat source to the existing coolant path.

If the outlet temperature were high, the solution might be more flow. If the inlet temperature were high, the solution would be a more effective radiator. But those do not appear to be the problems.

I think you're pushing Tesla's motor design into territory for which it was never intended. The cooling is only expected to keep up with average street demands, of perhaps 30 kW motor power; high power is only expected for one stoplight drag race or freeway on-ramp at at time. The heat of high-power bursts is soaked up by motor mass, the way the heat of a single stop is soaked up by brake rotor mass, with the assumption that a much longer cooling period will be available. Higher average power seems to be too much for it.

Leaf motors may have a similar issue, since they are not intended for sustained high power service, either.

I'm looking forward to seeing how this is resolved.
 

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I understand there is a difference between the temperature limit of the motor (being a higher limit) and the inverter (being a lower limit) and for some reason the coolant flows from the motor to the inverter.
is it possible to reverse the flow so it does the opposite? or separate the two with different cooling systems.
I also understand the piece at the end of the motor the funnels to coolant into the motor and then to the inverter is one piece so this would need to be redesigned.
 
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