# which motor for direct drive?



## neanderthal (Jul 24, 2008)

I am converting a 1985 rx-7 it is a light little car 2300 lbs stock I have already bought most of the parts i am using kinetik agm batteries and the 144v battery pack will end up about 470 lbs I have a 1000 amp controller from logisystems. So the car will end up weighing 2300-2500lbs when im through. 

I am going with a direct drive setup the motors im considering are these

9 inch adc 
9 inch warp or impulse
9 inch transwarp
11 inch warp or transwarp ??? (expensive only if the 9 inch ones are not powerful enough)

I want the car to be quick and fun to drive

the only reason in considering the transwarp motors is because of the cool tailshaft depending on how much it would cost to machine a piece one the other motors, the transwarp might be more cost effective

I guess my real question is this Will a 9 inch motor be enough to make my car fun to drive in a direct drive setup with a 1000 amp controller?


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## madderscience (Jun 28, 2008)

probably the 9" warp is your best bet.

the 11" will not have a very high top RPM so you would have a car with heaps of torque but no top end. (bigger motors are more torquey but will not spin as fast under the same load at the same input voltage)

Also, find and install the highest ratio rear end you can find. (hopefully around 4.7:1) and use the smallest diameter tires that will fit your car and roll easily, to further increase the effective gear ratio.

Good luck.


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## neanderthal (Jul 24, 2008)

hey ok thats a great piece of advice thanks a lot

now i was leaning toward the warp 9'' but the problem is they are backordered a few months pretty much everywhere i am hoping to get this car on the road soon 

do you guys think that the other motors i listed ( the adc 9'' or impulse 9'') can provide the required power? Im sure even an 8'' motor could drive the car, but iam am hoping to have a quick car that is fun to drive


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## madderscience (Jun 28, 2008)

in a direct drive situation a too small motor will overheat and/or burn out, and might not have enough power on the hills regardless of how many amps you are cooking it with. 

The bigger ones are probably still too big in your case. You aren't building a truck.

I would say you should probably just wait for the right motor. Waiting sucks, but not as much as getting the wrong motor and being dissatisfied with the performance and/or damaging it.

Chances are there are enough other parts of your project to keep you pretty busy while waiting for parts. Such was the case with my car, where the charger showed up later than everything else but I had lots of wiring work and dent repairs to keep me busy.


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## Qer (May 7, 2008)

Direct drive will probably equal a very low rpm on the motor for long times (like if you're traveling in a city) which will mean that the built in fan won't cool it well enough (especially at high amps). You will probably have to add an external fan that blows air on the motor, otherwise the brushes might go bye-bye on you.


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## john818 (Aug 1, 2008)

I'm wondering about direct drive too. To stay on topic, I'll use neanderthal's example.

If my quick research and calculations are correct, the Warp 9 is good for 5500 rpm, a 1985 RX-7 GSL-SE has a stock tire size of 205/60-14, and its Final Drive Ratio is 4.0 to 1 (non-SEs are 3.9:1). If my math is right, that's a theoretical top speed of about 95 mph.

Noob that I am, I don't know, but that sounds too high. I would guess that accelerating at low speeds would be slow and hard on the motor and other electronics. Am I right?

Say neanderthal found some kind of gear reduction (swap the differential, smaller diameter tires, or even chain drive) and topped out at 70 mph at 5500 rpm, would that give him "fun to drive" acceleration? If not off the line, maybe from a rolling start? How about with additional cooling like Qer suggests?

My uneducated guess would be that it wouldn't work well either. In a single DC motor application do you need some kind of transmission for good acceleration and highway speeds?

I've heard people talk about series-parallel switching of dual motors to get a wider range of performance. Does this work well for direct drive? Too complicated for what it's worth?


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