# Motor per wheel?



## Sunking (Aug 10, 2009)

Aelwero said:


> What's the advantages and disadvantages of running a single motor at each wheel?


Advantage = Traction and performance.
Disadvantage = Cost, complexity, and efficiency.


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## Anaerin (Feb 4, 2009)

Aelwero said:


> ...with individual contactors on each motor so that any one can be individually "shut off"... (for two main reasons... first being efficiency, sort of like how modern ICE's shut off half their cylinders at speed, and the other is for off road purposes... It's not uncommon to have one or more wheels leave the ground)


If the motors are AC, you wouldn't have to worry about shutting them off if they're off the ground. Your controller demands a certain RPM from the motors, and they match that RPM as close as they can. If the wheel is off the ground, the motor can match the RPM exactly, and as there's no resistance on the wheel it takes almost no power to do so. 

As for efficiency, ICE motors turn off cylinders as it's the only way they have to reduce fuel consumption (You can't really make a "bang" in a piston any less strong). Electric motors can reduce their power consumption to zero, and as they have considerably less rotational mass than a full engine + clutch + gearbox + transmission + differential(s) set, it takes less power to change their speed, and causes less drag when they're freewheeling.


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## DavidDymaxion (Dec 1, 2008)

I have thought this would be fun with an AWD car. Here are some pluses and minuses:


Might be cheaper
You could set a low voltage NEDRA record
You can run a lower system voltage
Redundancy for reliability
A bit less efficient (more motor friction) than a single big motor
More drivetrain friction
If you have 4 motors, it might be more efficient to run all four all the time rather than switch some off. The wheels will have a little bit less rolling resistance if they are all driven. You might have a bit less resistive loss, too, as with I^2R effects each motor getting 1/4 current will produce less I^2R heat than one motor at 4x the current. Note this assumes four equal motors, this doesn't apply to four small motors vs. one large motor.


Aelwero said:


> What's the advantages and disadvantages of running a single motor at each wheel?
> 
> I'm thinking one "supply system" (controller) with output to all four motors, with individual contactors on each motor so that any one can be individually "shut off"... (for two main reasons... first being efficiency, sort of like how modern ICE's shut off half their cylinders at speed, and the other is for off road purposes... It's not uncommon to have one or more wheels leave the ground)
> 
> How big would the motors need to be at a minimum if there were 4 drive motors and max speed expectations were very low (so long as torque is kept fairly high)... say 55MPH top speed with a 20 mile range on cheap car batteries for starters?


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## Aelwero (Aug 24, 2010)

Thanks guys  I'm on the fence between electric motors at each wheel and a central electrically powered hydraulic to feed 4 hydraulic motors... and I'm a little gimped by approaching it from a "physics guy" perspective 

Started two separate threads because it would get a bit confusing talking about both ideas in one thread.

Your AC explanation is way over my head Anaerin, but I follow what you're saying thank goodness  I don't actually need to go that complicated with it because those off camber situations where a tire leaves the ground normally happen at very low speeds (although I did once go up on my two left side tires going about 35MPH ) and it would be feasible to manually switch that one off camber wheel off manually from the cab... like with a contactor (do you guys call them contactors? big giant circuit breakers... bus bar in em, operated with a small control voltage to shut off high voltage lines.. I work on radars and in radar parlance, they are contactors)

Anyways... a viable commuter vehicle isn't the goal. My jeep is a toy, and will always be a toy. Why not tear it up and see what I can do with nontraditional concepts on an off road jeep? I have the advantage of vehicle laws being negotiable in my case... If I wind up not street legal, I'll just trailer it out to the trails... jeepers do it all the time


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## Bfalken (Apr 29, 2009)

Aelwero said:


> Anyways... a viable commuter vehicle isn't the goal. My jeep is a toy, and will always be a toy. Why not tear it up and see what I can do with nontraditional concepts on an off road jeep? I have the advantage of vehicle laws being negotiable in my case... If I wind up not street legal, I'll just trailer it out to the trails... jeepers do it all the time


I think a electric mud churning - rock crawling truck would be great idea. but I think your going to need some kind of transmission/transfer case to give you both axle twisting-vertical rock climbing torque and still have a reasonable cruising speed. Electric motors have a lot of torque throughout their rpm range but there is a limit to how fast you can spin them. 

Bob


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## Aelwero (Aug 24, 2010)

Bfalken said:


> I think a electric mud churning - rock crawling truck would be great idea. but I think your going to need some kind of transmission/transfer case to give you both axle twisting-vertical rock climbing torque and still have a reasonable cruising speed. Electric motors have a lot of torque throughout their rpm range but there is a limit to how fast you can spin them.
> 
> Bob



Yep. Based on the feedback, and some key points, I'm pretty much ruling out electric direct drive. The amount of power isn't an issue, it's the ridiculously LARGE transfer at low speed (jeeps occasionally break axle shafts... lot of power to push through wires). 

I started another thread in tandem with this one, on using electrically driven hydraulic drive, and I think that's much more suited to what I'm trying to do, and from a "jeep guy" standpoint, it's making a whole lot more sense  Going to pursue hybrid instead of electric, but it still could be powered solely on batteries...

I do appreciate the insights though


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