# Challenge: Multiple Motors in Series



## ithinkidontknow (May 14, 2009)

I have an electrical engineering question for all you electrical engineers!

If I have multiple motors in series, there will be a voltage drop due to the internal resistance of the motors. What will this look like for the motors? Will each motor experience a different voltage or will the voltage they receive be identical? In other words, will they all act identically (RPM, torque, etc.)?

For each of the motors in series to act identically to a single motor, what would have to change about the battery or controller input to the motors (in terms of the current, voltage, etc.)?

If anyone could give some insight on this matter I really appreciate it!

Thanks


----------



## speedster (Apr 4, 2009)

My 2 cents....
Each motor will have its own set of characteristics so *exact* identical performance tends to be a bit of a myth. Plus there is no way you can confirm your power pack's behavior, that is it power deliver to each motor will not be a constant either. Just connecting two motors together in series (electrically) IMO will not give you a output usable in a EV application. You will need to have some form of mechanical binding or controller regulation.

Some thoughts....
You will need to bind the output of the two motors, together via their rotor shafts or via a dual motor gearbox. Large heavy EVs like buses and trucks sometime use a single gearbox sporting a dual motor system. 
If you look at the White Zombie specs you can see how it migrated from a drive system that initially bound two motors together via their rotor shafts to a custom _single shaft _sporting dual rotors. This appears to be built specifically for the White Zombie application (high torque EV drag racing). The custom rotor does away with any potential mechanical weak point, possible where two motors with separate rotors are bound. There's probably some electronic control in the White Zombie setup too plus there is a mechanical differential on the final rear drive train.

If your using the motors in *dual* *direct drive* mode delivering their output independently to two separate drive trains e.g. separate wheels you will need a advanced controller than can monitor and mange both motors safely, thus allowing them to produce a regulated output to their independent drive trains (electronic differential). If you advance the control far enough should give you some tight turning circles lol!

I'm hoping, over time, to get a dual motor configuration together but have no experience of it yet.


----------

