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=18839I 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 Now the Leaf motor originally made 80kW (107 hp), but with a new brain board in the inverter, people have managed to get closer to 140kW (187 horsepower).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!
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torque.png
I also later used some simulation software to get an idea of what to expect.
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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.
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Front motor test.JPG
Then I decided to just mount the damn thing in the rear and take the opportunity to design an IRS.
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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).
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rear uprights.JPG
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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).
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APPS top.jpg
And here is the motor, gearbox and inverter installed, along with the HV charger off to the right.
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trunk.jpg