# EV SCCA A-Mod Car... feasible?



## ftaffy (Mar 13, 2009)

Looks interesting, Thats some high currents! I like the design, though do you really use that big wings? 
Also have you thought about the power vs weight of 4 motors vs say 2 twin shaft motors? This is something we expored in the SAE car (below) but ended up with the simpler option of a single motor.

There is something similar in the SAE Cars, RMIT has built an electric one: http://www.fsae.rmit.edu.au/

Was not allowed to compete but was quicker then some of the cars, for some more info see this thread at AEVA: http://www.aeva.asn.au/forums/forum_posts.asp?TID=718&PN=2

And a review of the weekend http://www.saea.com.au/wp-content/uploads/2009/02/formula-2008-report.pdf


Some things we found:
Spreadsheet calcs are great until you start to run it. We found that our gearing ratio was way out! So i just went to got a pile of sprockets from a local supplier and just kept running test till we got a good one.

Pick your controller carefully: We could not get hard acceleration from stop due to interal controller protection. Once going was brilliant, the coasting in corners made it very easy to get quick times.

Be very mindful of overcurrent draw, we melted a couple of thundersky batteries during out final run when we just kept going until the warning buzzers were going nuts.

With the connections between wires, use VERY solid and firm connectors. We had alot of problems to start with due to how hard we would turn.

The battery terminals need to be protected in the case of a HEAVY crash so that they cannot become in contact with the rest of the vehicle. This was a big thing with the judges before we were allowed on track.


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## john818 (Aug 1, 2008)

Way cool cars! Both GTLock13's concept and ftaffy's electric FSAE!

Sorry, I can't offer much advice. I'm a noob in both the EV world and homebuilt car world, but I'm trying to learn about both before I begin my project, whatever it ends up being. I do have a couple of comments and questions though.

*GTLock13 -* Like ftaffy touched on, from what I've read (I'm a noob, remember?), getting multiple motors to work together can be tricky, especially if you're running one at each corner. The controller(s) might be the problem. I could be wrong, but you might want to look into it. Also, is that a starter battery? I don't know if racing applications are different, but starter batteries generally don't work well in EVs. Something about them not being able to handle high levels of current for prolonged periods. Oh, and you might want to think about how many runs you can get without recharging or swapping packs. Maybe you can charge at the track. I've seen EV drag racers do that. Then again, if this is just a design exercise, maybe you don't care. I'm not trying to discourage you. Just trying to offer constructive criticism.

*ftaffy -* If you don't mind my asking (and sorry for taking this off topic), did you use a transmission? I assume you had a differential. Did you run a chain drive to a transaxle, like a Quaife or something? Or did you somehow mate a motorcycle transmission to the motor? I've been thinking about building a reverse trike (2 front, 1 rear wheel), but I don't see an easy way to go from motor to transmission to chain drive. Just wondering what you did. Thanks.


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## ftaffy (Mar 13, 2009)

john818 said:


> *ftaffy -* If you don't mind my asking (and sorry for taking this off topic), did you use a transmission? I assume you had a differential. Did you run a chain drive to a transaxle, like a Quaife or something? Or did you somehow mate a motorcycle transmission to the motor? I've been thinking about building a reverse trike (2 front, 1 rear wheel), but I don't see an easy way to go from motor to transmission to chain drive. Just wondering what you did. Thanks.


No Diff, used a set up called a Cush Drive, which is found in motorbikes. Basically its an insert which goes between the sprocket and the axle and removes the metal on metal contact. Its softer then metal but still hard, so the its a shock absorbing layer that still transmits power from sprocket to axle to wheels.
The chain goes straight to this sprocket. No trasmission, direct drive to the rear. At the AEVA site we are currently exploring the options available of running a 2 speed gear box with an EV, CVT's are looking like a likely route at the sec.

There are a few vids up on youtube of it, should put up some later ones when i had the brakes off set so it spun when you jammed the brakes on.


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## GTLocke13 (Mar 25, 2009)

They're AGM motorcycle batteries. With keeping the weight low total stored energy isn't the big thing, I just need high power output with low weight. I think the EV drag guys use them. Are there batteries with a better power to weight ratio out there?

I would probably try to run the motors on a single controller if possible and just wire the motors in parallel (or is it series? One of them acts like a LSD). I was looking at the Zilla when I was first pondering this. It seems like now there are more high-end controllers out there as well.

You wouldn't want to use a twin shaft motor for 1) packaging - width is critical on an autocross course and 2) you would need a differential.

And yes, they do use wings that big:


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## ftaffy (Mar 13, 2009)

Look at Lithium Ion batteries, they are what we ran. 96V @ 40AH gave use ~20mins (hard) run time @ 200A. They blow lead acids away for power/weight.

Zilla no longer make controllers, you will need either a custom or your choice is limited (The Amps your talking). I am currently looking for a controller for my Lotus 7 EV but looking in the 750-1000Amp range. 750 Amps would give me enough power to do 0-100 in 5 sec (in theory lol, i know of someone who tried to do this and it flopped.)

Not saying it cant be done but 4 x motors and controlling them is going to be a difficult task as you said. 1 controller for 4 motors, not too sure about this. Maybe someone who has run a 2motor set up can comment. You will actually want the motors to switch between parallel and series, gives you more torque then more rpm as you accelerate. It was an option we were looking at, maybe look at the mini EV that runs 4 x hub motors and see if you can find out how they did it

Series you split voltage (but same current across each motor = torque), parrallel you split current (But same voltage across each motor = speed). - I think i got that right... please correct me if my mind is backwards today.

The question is, do you really need indepdent wheels or can you run no diff. It does make it a pain in the arse to push the car around but once at speed its fine.


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## DavidDymaxion (Dec 1, 2008)

http://sccaforums.com/forums/thread/179961.aspx has a thread on electric A-Mod cars.


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## epyon (Mar 20, 2008)

I would use diff's in the front and back and a motor on each . That should help get it off the line . It's how I would build a street car . I wished I lived near you so I could help or see you race . I live in Las Vegas and I don't get any help with my car at all . And I already got the parts .


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## jr dragster (Oct 11, 2010)

heres a gear grinder it might help you some with the gearing ,we used it one the jr dragster and it was close to what it was running.
http://www.jrdragsterplus.com/geargrndr.htm


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## mizlplix (May 1, 2011)

This would be a perfect project for wheel speed sensors and traction control. It would be a nice match. 

Our race team had this set up back in 1995 in a World Challenge Cup car. {illegal I know}

We had to do a last minute percentage adjustment just before the race to correct for weather and temps. BUT, The drivers could just bury the throttle on exit and worry about other things. 

Yes, the cars were noticeably quicker. We did back up runs with it on/off on every track'

Miz


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