# Motor in place of diff on IRS?



## booksix (Aug 26, 2008)

Ok, so I HATE the idea of not having a clutch and shifter for my car, but I'm just thinking about some cool setups.

I'm am just finishing up an custom install of an 03 Mustang Cobra IRS (independent rear suspension - in case you didn't know) rear-end in my 88 Thunderbird Turbo Coupe. It has a complete subframe that bolts to the chassis and the rear-end goes in it. I was thinking, it'd be really cool to replace the pumpkin with a double shaft motor. But, for it to be realistic, I guess you'd need some kind of gear reduction between the motor shaft and the half-shafts (that could handle some serious high voltage torque). Anyone know of anything out there that could work? If I could figure it out I'd eventually want to retrofit a front drive setup into the car and have 2 dbl shaft engines and AWD...


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## TX_Dj (Jul 25, 2008)

Yes, you could do it... but here are the factors to consider...

1) if you connect the half shafts to each tailshaft on the motor, you no longer have a differential, and driving this vehicle will be like driving a spool rear end. Can the motor you choose hold up to the stresses of turning on pavement with one side hopping and jerking trying to keep up with the other side?

2) You will need a seriously beefy motor & controller, and a wild battery setup to handle the sort of amps necessary to turn at 600-700 RPM at freeway speeds without any gear reduction. Expect range to be low, and motors to require severely frequent maintenance and/or rebuilds.

Yes, gear reduction is key. When guys like NEDRA draggers talk about "direct drive", quite often they mean directly driving the differential- not the axles themselves. If you have a tire that rolls out 700 revs per mile, then at 100 MPH you'll have to be turning it at 1200 RPM. If your motor has a max speed of 5000 RPM, then the lowest ratio you can run to turn the wheels at that speed is 4.16:1, which is within the scope of what a diff can provide.

Even still, such a setup is not well suited to daily driver use, but is quite well suited to 1/4 mile strip use. Because even then, that ratio is so high that it will require incredible motor amps at a dead stop to get the car running, which eats your brushses and commutator alive.

Thats why we retain the ICE transmission on the road and typically shift between 2 or 3 ratios, depending on what the overall ratio (gear ratio * diff ratio) and tire diameter are.

Clutch is purely optional, only needed if you have trouble shifting gears in motion, which is far easier on EV than on ICE on most transmissions. That's the only time the clutch is used on an EV, and in fact, because of that, if you convert your vehicle with a new clutch, machined flywheel, and pressure plate, your clutch is likely to slip like mad because it can't "break in" like it would in an ICE, where it must slip a bit every time you start rolling the vehicle.


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## booksix (Aug 26, 2008)

I figured there'd be some issues like this. Just thought it'd be cool to setup it up this way. I was thinking some kind of gear box that would allow a limited slip type function on each side. Anyway, just fun thoughts... too expensive for me, atleast right now, but still sool to plan and get others inputs


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## Schmism (Aug 16, 2008)

on IRS there is a rear differential that is mounted to the body.

instead of driving the front drive flange with a drive shaft, mount your motor to it and drive it directly off the motor.

you remove the transmission, remove the driveling, and am able to keep a gear reduction for the motor as well as retain the diffrental speed for turning.

I know bmw rear diffs range from about 3.07 to 4.27... you can even include a LSD.

to find out what your current gear reduction is, (assuming you use 2nd almost all the time) take your second gear ratio and mulipuly it by your rear end ratio.

to pretend you have no transmission reduction just the rear end, use 3rd or 4th as they are close to 1:1 (5th is usually an overdrive if you have it)


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## booksix (Aug 26, 2008)

well, the goal wasn't to remove the transmission. If I wanted to a setup like that I'd keep the clutch and trans. The reason I asked about the possibility of the above setup was to create a twin motor AWD car where each motor ran 2 wheels with gear reduction in between. Basically, trying to build a lighter AWD car (no transmission, transfer case, etc...)


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## OHM (Jun 30, 2008)

http://www.diyelectriccar.com/forums/showthread.php?p=67100#post67100

My topic of  * DC motor and differential all in one!!!

Ive found a supplier but cant get a response on information.
Does anyone speak Italian that can contact them?

*This little beauty from Best Motors in Italy 
Could be used with two separate short drive-shafts

Look under ¨Traction DC motors¨

http://www.bestmotor.it/frameset_ei.html

15kw or 20hp nominal


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