# Transmissions, hub motors and electric vehicles



## major (Apr 4, 2008)

pengyou said:


> The use of hub motors seems to have fallen out of favor. Why is that?


http://www.diyelectriccar.com/forums/showthread.php?t=20591&highlight=wheelmotor

It is a product everyone wants but nobody has. You can find lots of discussion here and other places.



pengyou said:


> Also, related to the hubmotor question, there was talk of an "electronic" transmission that would manage the electricity to the motor - or motors, in the case of 4 hub motors - so that a mechanical transmission would not be necessary. What happened to this idea?


It's called the motor controller. And shifting transmissions are not necessary in EVs. None of the commercially available EVs use a multiple ratio gearbox.


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## pengyou (Nov 21, 2012)

Thanks! What about differentials? If a separate motor were used for each wheel would a differential be required to maintain the proper speed during a turn?


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## Frank (Dec 6, 2008)

That's an interesting question and one I've pondered from time to time. If I were doing it I think I would start with the assumption that a differential action would happen automatically and if it became an issue, worry about it later. That would be the least of your problems if you used a separate motor for each wheel anyway.


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## pengyou (Nov 21, 2012)

"That would be the least of your problems if you used a separate motor for each wheel anyway"

What would be the bigger problems with separate motors for each wheel?


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## major (Apr 4, 2008)

pengyou said:


> What about differentials? If a separate motor were used for each wheel would a differential be required to maintain the proper speed during a turn?


http://www.diyelectriccar.com/forums/showthread.php?t=82349&highlight=mira

Lots of ways to make EVs  Choose one and go for it.


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## pengyou (Nov 21, 2012)

major said:


> http://www.diyelectriccar.com/forums/showthread.php?t=82349&highlight=mira
> 
> Lots of ways to make EVs  Choose one and go for it.


You are right, but, unfortunately, I am not independently wealthy so I want to look at what others have done, learn from their successes and failures and then go from there. I am willing to try something a little bit new but I have to make sure that there is enough science to substantiate trying it. One of the reasons why I want to electrify a VW-dune buggy is that it has a solid steel frame, rather than unibody, which means that it is less trouble to make a serious modification. There are also more spaces in this body to hide batteries, i.e. up in the front trunk (where the gas tank used to be, under seat pedestals, and, without an engine, where the engine used to be. The distribution of weight in this vehicle should be pretty close to ideal.


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## gunnarhs (Apr 24, 2012)

pengyou said:


> You are right, but, unfortunately, I am not independently wealthy so I want to look at what others have done, learn from their successes and failures and then go from there.


OK, then you are DIY like most of us here and you will then be limited to conversion. You will certainly not be using many (hub?) motors then...



> I am willing to try something a little bit new but I have to make sure that there is enough science to substantiate trying it.


Most DIY-experience is with DC-series-motors, but the science is also quite solid for Sep-Ex DC (hard to find a good controller though) and AC-(Induction /PMSM/BLDC)


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## Frank (Dec 6, 2008)

pengyou said:


> What would be the bigger problems with separate motors for each wheel?


How will you physically connect the motor output to each wheel? (Hub motors are a theoretically nice way to do this but in practice have many issues.) Chain or belt drive? Driveshaft? Have you thought about unsprung weight and suspension geometry? These problems go away if you eliminate the suspension but that won't make a very practical vehicle. Using a single motor (or two motors coupled together before the rest of the drivetrain) allows you to use more OEM parts which saves a lot of headaches in the long run.

Having said this I don't mean to discourage you! If you want to pursue an innovative way for your EV - go for it! Just be aware that solutions tend to coalesce to what's already on the road for good reasons.


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## pengyou (Nov 21, 2012)

I am not sure what I will be buying at this point. I want to pick some brains first so that I know what questions to ask, and then study those questions to find the answers. 

RE: installing hub motors, a more likely scenario would be to weld an assembly to the frame and install the motor to that assembly and connect the motor to the wheel with a cv joint. That would eliminate the problem of the unsprung weight issue, I think, as well as the suspension geometry issues...at least, in theory. I have seen 10hp golf cart motors - 48 volt - that will push that little roller skate up to 24 mph with a 10" wheel...I know that a car weighs at least twice as much as the cart, but (if the multiple motor idea works) there would be 2 motors upfront working in tandem turning a 15" wheel, and possibly a third or third and fourth in the rear. Assuming that the motors have adequate torque, 30 mph should be reasonable. This motor was about $400. 4 10 hp motors...need 4 controllers..but I know from experience working with electric bicycles that if the voltage/wattage of a motor doubles, the cost of the controller (if in the upper ranges) more than doubles - sometimes triples or quadruples, so it might be cheaper to use 4 of these motors...The question then is whether or not such a motor would be durable...are there power losses using multiple motors? how would these compare to the power loss of using a differential? etc...many questions. But right now, I am just happy to pick the brains of such an informed group of people. Every point you mention gives me something more to study.


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