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PostPosted: November 19, 2023, 2:17 am 
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I figured I should start a new thread to cover the electric conversion of my R1-powered book build. Original build thread wasn't very detailed, but can be found here: viewtopic.php?t=18839


I finished the car in 2019 and autocrossed it every season except this past one. It was a lot of fun, but I had several gripes.

-Too loud: Even with the biggest muffler I could find, plus a muffler insert in the collector, I was getting sound warnings every other event. Sometimes going over.
-No torque/abysmal launches: Sure the thing had a heavy duty clutch, but it just did not have the torque to make a good launch. Below 5000 RPM it was not fun.
-Bad gearing: The rear end was 3.45:1, I could have gone as high as 4.56 but that would make it undriveable on the highway. With the 3.45 gears I was still around 5000 RPM at highway speed.

So, I figured electrification could be a cool evolution of the car. After a lot of research, I decided a cost effective solution would be a motor from a Nissan Leaf, and batteries from a Chrysler Pacifica hybrid minivan. The Leaf motor is about the same weight as the solid axle it would be replacing, and the batteries were only a bit heavier than the bike engine (228 lbs for 16kWh). Having a bit more front weight wouldn't be the worst thing either, since the car only came in at 1200 lbs with the bike engine, but about 65% of that was on the rear wheels. Removing the bike engine, solid axle, driveshaft, reverse box, fuel tank, and adding back the Leaf motor, reducer, batteries, new rear wishbones.. It will be interesting to see what it weighs in at after all is said and done.

Then there's the matter of performance to consider. Everyone knows electrics have full torque right off the line, but the horsepower numbers can be deceiving. I was running most autocross courses entirely in first gear (since it could go more than 60mph in 1st). So, I made a comparison chart. Now the Leaf motor originally made 80kW (107 hp), but with a new brain board in the inverter, people have managed to get closer to 140kW (187 horsepower). Basically just more torque at a given RPM. Here's a spreadsheet I made by taking a dyno graph of a R1 motor, adjusted for my altitude, and multiplied by the final drive to get the actual wheel torque at a given speed. Then I did the same for the electric motor. I think the numbers speak for themselves!

Attachment:
torque.png


I also later used some simulation software to get an idea of what to expect.

Attachment:
FOC charts.JPG


Then there's the question of range. I don't want to carry more weight in battery than absolutely necessary, as long as I can get some kind of decent drive in. I found a formula to estimate watt draw at speed, but you need to know your drag coefficient and frontal area. I googled it and found that a locost can be as high as .75 drag coefficient. I had to take a bit of a WAG at the frontal area, but figured about 16 sq ft. With those numbers I could drive 60mph for one hour. Or 50mph for almost 2 hours. Or 35mph for over 4 hours... I think that's good enough. Happy to share the math if anyone is interested.


Alright, now that the justification is out of the way, here's my progress to date. Last year my wife and I welcomed our first child into the world, so progress has been a bit slower than I had hoped, but hey, priorities.

So I did briefly look at mounting the electric motor up front and keeping the solid rear axle, but the ratio of the axle itself wasn't quite right and the battery arrangement was abysmal. I was also assuming I'd be using an 18kWh battery out of a Chevy Volt. Those batteries are arranged in a pretty inefficient way, and nothing I could come up with looked like a good solution.
Attachment:
Front motor test.JPG


Then I decided to just mount the damn thing in the rear and take the opportunity to design an IRS.

Attachment:
IRS testing.JPG


New uprights CNC'd, and they accept the same SN95 Mustang rear brakes I had been using, but with a Nissan Leaf hub (same bolt pattern thank the stars).

Attachment:
rear uprights.JPG


Attachment:
irs test fit.png


CNC'd parts to convert the Wilwood throttle pedal to work with a hall sensor (used part of the old cable linkage for a return spring).

Attachment:
APPS top.jpg


And here is the motor, gearbox and inverter installed, along with the HV charger off to the right.
Attachment:
trunk.jpg


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Last edited by ZiG on November 19, 2023, 2:37 am, edited 1 time in total.

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PostPosted: November 19, 2023, 2:28 am 
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Now I also had to mount the drive unit backwards to how it was originally installed in the Nissan. Not a big deal since the inverter control board can apply full power in either direction, but the reducer box does use a splash lube system. So I grabbed an electric scavenge pump from a BMW and machined a new block for it, then plumbed it into the transmission. Now it will fill up the same reservoir that was fed by the ring gear splash, which drips onto the intermediate shaft/bearings. I also added a couple holes and channels to feed more directly into the bearings. The pump has a decent flow rate so hopefully it all works out. Apparently others have had success with running these in reverse anyway.

Attachment:
oil pump.JPG


Attachment:
oil channel.JPG


Wiring the battery management system. Had to repin connectors for 96 cells and 10 thermocouples...
Attachment:
bms wiring.png


Battery enclosure. The battery is divided into 2 modules that I was forced to stack vertically. The top and one side of this frame comes off to facilitate installation into the car. Then aluminum panels cover all sides.
Attachment:
Screenshot 2023-10-03 172935.png


And, actually I'm not happy with how it turned out. The panels don't fit very well across the front. But lucky me! The SCCA has released a set of draft rules for EVs that would make this box illegal anyway So I have the perfect excuse to remake it out of 1/8" aluminum. That'll be a winter project...
Attachment:
Screenshot 2023-08-16 203827.png


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PostPosted: November 19, 2023, 3:02 am 
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Now all you need is to tow an inversion generator when driving on the street.

Congrats on a wycked build :cheers:

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My build log viewtopic.php?f=36&t=10658&start=0 NOW NAMED =The Wycked 7

My other build log viewtopic.php?f=18&t=15162 The Skayt'R6


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PostPosted: November 19, 2023, 3:21 am 
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Haha, thanks. I have considered a cheap generator in my hauler.. Or a big inverter since it has the dual 200a alternator package. Probably won't go through too much juice in 8-10 runs at autox though. The onboard charger will take like 5 hours to go from 0-100%, but if I add some hardware I could add fast charging at a public station, probably take as little as 20 minutes if the cooling system can keep up.


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PostPosted: December 26, 2023, 4:14 pm 
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ZiG wrote:
Haha, thanks. I have considered a cheap generator in my hauler.. Or a big inverter since it has the dual 200a alternator package. Probably won't go through too much juice in 8-10 runs at autox though. The onboard charger will take like 5 hours to go from 0-100%, but if I add some hardware I could add fast charging at a public station, probably take as little as 20 minutes if the cooling system can keep up.

I'm really looking forward to watching this progress. My Chevy Bolt goes through ~1kWh / run when I autox it (70-75 second course) for reference. With less power and weight I'm sure you'll use less than that.


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PostPosted: January 3, 2024, 12:55 am 
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Oh, awesome! I was figuring it would be somewhere in that ballpark, good to get some confirmation.

As for recent progress, I got the suspension assembled to the point where I was confident taking measurements for new axles. One needed to be shortened only slightly, the other needed a good few inches taken off. Unfortunately shortening the axle only a little bit is not possible due to how the diameter is reduced near the ends. So, I had one shortened and one made completely new. This one also didn't have the same diameter reduction machined in, which I suppose is okay because it will help to limit the torsional deflection and hopefully prevent any noticeable torque steer issues (Yes I know it's RWD but Caterham actually had a bit of a torque steer issue on their cars before they were able to center the rear diff.... allegedly).

I have also been working on ensuring the car is compliant with the new SCCA rules, which necessitated getting an insulation monitoring device. Found an ISO165c-1 in new condition on eBay, so that's somewhere in the mail now, along with about $100 worth of connectors, indicator lights, resistors etc to hook it all up.

After installing the axles I decided I was at a good place to do a test of the motor while connected to the HV battery. I had previously done a basic spin test with three 20v Dewalt batteries in series to verify the accelerator pedal sensor was working and that all the wiring was done correctly. I didn't want to feed it higher voltage until I had the axles installed so I could stomp on the brakes if it tried to spin up uncontrollably or something. Thankfully, the test went fine.

And I figured what the hell, adding a rasyberry pi to the dash with Android Auto and it will also be tied into the inverter and master control unit, so I can datalog and tune on the fly. Still working on that, more on it later.

Axles:
Attachment:
axles.jpg


Cleaned and re-greased all CV joints plus new boots all around:
Attachment:
CV joints.jpg


Also took the time to figure out a way to cover up the giant hole in my hood from where the ICE air intake sat:
Attachment:
louvers.jpg


Axles in:
Attachment:
axles in.jpg


Motor wired up:
Attachment:
motor.jpg


J1772 charge plug, charge indicator (there's also a screen on the dash that will show more detailed info while charging) and coolant reservoir (location chosen due to it being the highest point in the system, since the coolant passes through the top of the component it's bolted to):
Attachment:
j1772.jpg


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PostPosted: January 3, 2024, 4:11 am 
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Superb writeup, brilliant project. Following with keen interest! :cheers:


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PostPosted: March 18, 2024, 12:43 am 
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Finally got the new battery enclosure finished. Funny enough my current job involves a fair bit of sheet metal design, so I was able to model something up and have it laser cut and CNC bent at Send Cut Send. They also installed PEM nuts which I wanted to use rather than rivnuts so as to avoid leaving a raised surface on the mating side of the sheet. Now since I was farming this work out I tried to be as cost effective as possible, making some parts identical for quantity discounts and then modifying them later. Very impressed with the quality of what came back, even the zero clearance holes I drew lined up perfectly, even around corners. I also made some of the brackets and the top plate myself, to save a bit of money. In some cases I did use rivnuts, but I counterbored the holes on my mill to get them to sit flush.

This was the basic design.
Attachment:
inventor.jpg

Contactor box with 3d printed parts.
Attachment:
contactor box empty.jpg


(And once it was installed, but only partially wired).
Attachment:
contactor box partially complete.jpg


First group of cells in place. The liner is Nomex 410 paper and Kapton tape. A requirement in the SCCA rulebook.
Attachment:
bottom pack installed.jpg


Mid tray (same part as the base tray but I cut the front off and bent it downward for rigidity).
Attachment:
mid tray.jpg


Top group of cells in place and most of the wiring done.
Attachment:
top pack installed.jpg


And done! I'll have to pull the lid off again later to check for leaks once I refill the coolant, though.
Attachment:
finished box lid on.jpg


I also decided to change up my accelerator pedal situation, so I removed the single channel hall sensor and modified a Prius pedal. Basically I cut the pedal part off, then mounted it upside down behind the Wilwood pedal box and connected it with a linkage. I also ran a nicer shielded wire, just in case. And then I forgot to take a picture. oops. Oh, and I discovered a small problem with myself while testing the feel of the pedal. I was checking to see how it felt to roll on and off (linearity, overall resistance, etc) and caught myself making engine noises as I did it.

Lastly, I have been working on the computer. The one on the left is a Raspberry Pi running Open Auto Pro, powered by a CarPiHat. It can communicate with the inverter over wifi, and the BMS/MCU via USB. Eventually I want to get it onto the CAN network for datalogging too. Possibly add a camera feed and run it with TrackAddict. The screen on the right is the Dilithium display for power usage, SOC, cell balance etc. The shroud I printed for the back was a tad too tall so the dash is sitting a bit high in this picture. Will have to print a new one asap. There's also a speedometer that will be mounted below the blue buttons but I can't mount that until I reinstall the cover for the transmission tunnel.
Attachment:
screens on.jpg


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PostPosted: March 18, 2024, 11:12 am 
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I came >this< close to building a third car, EV-based this time - but didn't. Why? This can either serve as a cautionary tale, or words from an old cynical car guy. Summed up, I found that driving a self-built high performance sports car on the street produced too much anxiety to be enjoyable for several reasons: Fear of damaging the drivetrain; concerns about not being seen, and the worst: traffic taking much the fun out of driving.

That said, for an autocross-only car, it's nearly perfect - except that around here, nearby venues have disappeared, and I've had my fill of autocross. My negativity aside, I'm curious what your total all-in cost will end up being. Also, are you driving the car to events or trailering it?

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Last edited by KB58 on March 18, 2024, 1:46 pm, edited 1 time in total.

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PostPosted: March 18, 2024, 11:52 am 
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I'm not tracking the cost too closely, it kind of is what it is at this point. I got a great deal on the battery and motor though, and did alright selling off all the old drivetrain components. That said, custom CV axles were a lot more expensive than I expected, and I've also had to spend more money on compliance with SCCA rules. Rules which didn't even exist when I started the conversion.

It's trailered to all autocross events, yes. Most of them are 1-2 hours away, so no chance I'd make it with a battery this light. I could have drove it with the bike engine, but chose not to because it would have meant an hour or two of 5000rpm down the highway each way.

I totally agree though, the lack of sound won't inspire confidence on the street. It should be better to drive in the city now, but I'll be far less inclined to do so!


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PostPosted: March 21, 2024, 5:47 pm 
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From another forum, and hope this won't impact you - but something to check on:
Quote:
An EV can work (quite well) for autocross, but keep in mind that tracks are increasingly banning EVs completely right now because they don't have the firefighting capability to put out a lithium battery fire. Also consider that even with a quick charger at the track (edit: a very optimistic assumption since few tracks have any chargers at all), you're probably going to be doing a number of laps per day that you can count on your fingers and toes.

Sadly with the new bans I think an EV makes even less sense as a track car right now than they did in 2021 when I thought long and hard about whether to buy another ICE vehicle and decided that an EV still didn't make sense as a track car.

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/


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PostPosted: March 22, 2024, 12:10 am 
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Ah, yes I'm aware of that. I didn't mention it on this thread, but I've been in direct contact with the SCCA committee who developed the supplemental rules for electric vehicles, and even got in on a recent meeting to answer questions about the rules once they were approved.

The bad news that the governing body for Alberta has indeed banned fully electric vehicles for the time being.

The good news is they are still fine in BC, so I could always head to Kelowna to get my fix (though probably not this year). The better news is the Canadian version of the FIA is working on their own EV rules and apparently they are close, though it still might not go into effect this season. My local autox clubs all reference the SCCA Solo rulebook and I have designed and built everything to be in compliance with the aforementioned EV supplemental.

Due to some life circumstances I may not have much time to autox it this summer anyway, so I think I'd be happy if I only got it out for some a few shakedown runs on the street this summer.


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PostPosted: March 22, 2024, 10:52 am 
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If the worst happens - that autocross isn't allowed - can additional batteries be added to make it road-going?

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Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/


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PostPosted: March 23, 2024, 10:28 am 
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I could add more capacity, but I doubt I'd bother. With 16kWh It should already have enough range for any drive I'd likely want to do (or have done in the past) according to the calculations in the first post. I could also add fast charging capability if I cared enough to bother. I will have regenerative braking turned off for autox out of fear of it unpredictably altering my brake balance, but for street driving I could always turn it back on if I wanted the extra range. Unfortunately I'd have to do that through the computer screen, rather than having a switch. You can adjust the portion of the pedal travel that is assigned to regen, so I'd have to go in and change the value from 0% to say 30% and hit save.


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