# Displacement on Demand (DOD) for electric motors?



## notailpipe (May 25, 2010)

Further, how would scenarios A, B, and C differ in performance, where:

A) Two motors connected at the shaft. Controller can either run motor 1 alone, or can run motors 1 AND 2, in *series* connection.

B) Two motors connected at the shaft. Controller can either run motor 1 alone, or can run motors 1 AND 2, in *parallel* connection.

C) Two motors connected at the shaft. Controller can either run them in parallel or in series. But either way, *BOTH* motors are on. i.e. White Zombie.


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## Frank (Dec 6, 2008)

I think DC series motors kind of do what you're suggesting automatically. ICE's have pumping losses and friction associated with each cylinder which is why deactivating cylinders allows them to work more efficiently. DC series motors have very low rotating friction and losses are proportional to I^2. It takes a certain amount of force (i.e. torque i.e. amps) to propel a vehicle down the road at a certain speed and I don't think it matters if that torque is created by one or two motors. Hmmm, maybe two motors are more efficient than one in this case? Not sure...

I do know that max output with DC series motors depends totally on batteries and controller. Think of the motor(s) as acting as a mechanical transformer: it/they will try to convert everything the controller/batteries can throw at them into mechanical motion.

I hope I understood your questions correctly!


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## DavidDymaxion (Dec 1, 2008)

That's a beauty of electric -- you give up almost nothing to have a fast one, unlike a gas car. You'll do maybe 100 or 200 lbs more motor, and 15 pounds more controller (~7% more weight), but the bigger motor is a bit more efficient so you get a little bit of that back.

An electric that has a high top speed will also tend to have good range.


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