# Wheel Hub Motors: Are they viable yet?



## major (Apr 4, 2008)

Yup. Wheelmotors still suck for anything larger than a bicycle or small scooter.

edit: here's one of my favorite threads on the subject:
http://www.diyelectriccar.com/forums/showthread.php/wheel-motor-affordable-20591.html


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## brian_ (Feb 7, 2017)

There are endless announcements of hub motor designs, and they all share the same problems:

Unspung weight is important to ride and handling. An electric motor of sufficient power (even for one wheel worth of propulsion) is heavy. The motor's weight can be minimized by operating it at high speed, but that means lots of gear reduction, which means a heavy, bulky, and expensive pile of mechanical hardware riding with the hub... increasing weight and packaging problems.
Electric-assist bikes and similar vehicles routinely don't even have suspension, negating this concern.​
High power density leads to the need for cooling, which means hoses carrying liquid coolant between the motor and radiator. While many (probably most) DIY EV conversions make do with no more cooling than a fan on the motor shaft, continuous-duty motors in commercially produced electric vehicles are typically liquid-cooled. With a wheel motor, that means hoses running along the suspension links, flexing with suspension travel, and flexing through even greater angles with steering.
Electric-assist bikes and similar vehicles typically run only a few hundred watts, which is relatively easily dissipated through the surface area. This is a scaling issue - sometimes smaller is easier.​
One reason to use a hub motor is to avoid the need for a jointed shaft to connect the hub to a motor or transmission... but those shafts are very effective and reliable, while a hub motor setup requires that the electric power cables flex with suspension and steering movement.
The cables for an electric-assist bike's hub motor are thin, minimizing the problem - this is the scaling issue again. Similarly, electrical cable to a wheel speed sender is not a problem, because the wires are thin.​
Although most braking effort for an electrically-driven wheel should be regenerative action by the motor, a mechanical brake is still needed to supplement regenerative braking, as a backup, or for parking. That's difficult to package in the hub assembly with a motor (and likely gearing as well). I noticed that a recent design actually used a drum brake, because it was easier to package than a disk brake, even though drums have long been obsolete for automotive use other than for parking.


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## brian_ (Feb 7, 2017)

major said:


> ... here's one of my favorite threads on the subject:
> http://www.diyelectriccar.com/forums/showthread.php/wheel-motor-affordable-20591.html


Thanks 
I'll apologize for having responded (my post above) without looking at this thread. I still haven't read the whole thread yet, but the fact that the person proposing to produce hub motors as a commercial product doesn't understand the meanings of "rotor" and "stator" is not a great start... and another dozen posts in he's talking about 96 volts of lead-acid battery, so it's not about wheel motors for a serious roadgoing car. Into post number twentysomething and we see that he was planning on an open motor, exposing the flux gap to road debris and brake dust!


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## brian_ (Feb 7, 2017)

Still reading the old (started in 2008) wheel motor thread...

It seems to me that many people proposing designs (such as the original poster in that thread) don't know much about automotive design. That's okay - I don't know much about inverter design, and we all need to start somewhere - but in many cases it seems like they haven't even taken a wheel off a car and looked at what is there!

At post #80, ten months into the discussion, the original poster finally realizes that inboard brakes exist. That's not surprising since most people - even many auto enthusiasts - are not familiar with inboard brakes, but his reaction is either disturbing or hilarious: he proposes mounting the motors in the hubs and brakes inboard, still requiring the halfshafts and putting the heaviest and most complex parts bouncing around with the hubs! Not a lot of rational thought going on here...


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## brian_ (Feb 7, 2017)

That classic wheel motor thread has a link (at post #165) into the middle of another thread. That one - _open source hub motor/wheel motor_ - runs to 481 posts , apparently with no viable wheel motor appearing.


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## USAVeteranRealtor (May 16, 2017)

Thanks for the input, i was thinking this was the case still, just wanted to ask to see if something new and amazing had come out that changed the situation... 

Another idea that has been bouncing around my head is placing the electric motors in the nose area of the vehicle in front of the passenger area which is typically filled with nothing or just the brake system. I could mount a pair of narrow motors so the shafts face outwards and possibly either gear drive or chain drive them to a centered area on the side of the passenger compartment which allows the ability to run a short axle from the output gear/sprocket to the wheel hub like how FWD cars are connected from the transmission to the front wheel hubs. Even if it was chain, probably be best to enclose it inside of something to prevent road trash on the chain and possibility of filling partially with oil/grease for lubrication. 

I still have a lot to learn, but curious if most motors could be wired up to spin opposite at the same rate of increased speed via the motor controller? so the 2 motors in the front would be somewhat equal in acceleration...


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## USAVeteranRealtor (May 16, 2017)

Another option is the use of hydraulics. You could use 1 single larger motor mounted somewhere, then coupled to a common hydraulic pump which feeds equal pressure to either 2 front wheels or all 3 wheels equally being powered by the electric motor, but i feel like this would be the slowest and heaviest route of going about it.


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## Karter2 (Nov 17, 2011)

USAVeteranRealtor said:


> My question is this... Have any wheel hub motors become viable yet in regards to reliability. I looked into this a few years back when i converted my catrike expedition to electric with a hub motor and nearly everyone told me that they were junk, that the wires would overheat at the center with any type of spirited driving.


 Reliability of direct drive hub motors is the least of their issues for vehicles above 200kg or so.
Bicycle /trike conversions are viable up to 3-5 kW , beyond that, the weight of motor and battery begins to move things up to a different power league.
Infact any "direct drive" ( motor running at wheel speed) becomes unattractive at those 200kg+ weights where torque becomes a serious requirement, and hence gear reduction between the motor and wheels is beneficial to get useful torque and efficiency.
There are several electric fwd "mototrikes" already available if you are looking for inspiration.
However, if i were building it, i would keep it simple with a geared ( chain) drive to the rear from a single chassis mounted motor, and solve the traction and handling issues with weight distribution and wheel/tire selection.


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## brian_ (Feb 7, 2017)

USAVeteranRealtor said:


> Another idea that has been bouncing around my head is placing the electric motors in the nose area of the vehicle in front of the passenger area which is typically filled with nothing or just the brake system. I could mount a pair of narrow motors so the shafts face outwards and possibly either gear drive or chain drive them to a centered area on the side of the passenger compartment which allows the ability to run a short axle from the output gear/sprocket to the wheel hub like how FWD cars are connected from the transmission to the front wheel hubs. Even if it was chain, probably be best to enclose it inside of something to prevent road trash on the chain and possibility of filling partially with oil/grease for lubrication.


After wading through the 39 pages of the other thread, I went for a walk and thought exactly the same thing: presumably the space directly between the front wheels is foot room, and so the interest in wheel motors, but you can still have individual motors without mounting them out at the wheels.

A more fundamental question might be why use this vehicle design, if radically changing the way it works? Three-wheelers have substantial challenges in dynamic behaviour, and the change from driving the rear wheels to driving the fronts has consequences. As Karter2 suggests, a more suitable design makes more sense.



USAVeteranRealtor said:


> I still have a lot to learn, but curious if most motors could be wired up to spin opposite at the same rate of increased speed via the motor controller? so the 2 motors in the front would be somewhat equal in acceleration...


I believe the answer is 'yes' regarding reversing motor rotation direction. Although some in this forum will tell you that individual motors are crazy and unworkable - and I agree that controlling them appropriately would be a challenge for DIY project - they are now done in a few production vehicles, so it is certainly a viable approach. Of course, every wheel motor design requires the same control of independent motors, but none of them have made it to production.


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## brian_ (Feb 7, 2017)

USAVeteranRealtor said:


> Another option is the use of hydraulics. You could use 1 single larger motor mounted somewhere, then coupled to a common hydraulic pump which feeds equal pressure to either 2 front wheels or all 3 wheels equally being powered by the electric motor, but i feel like this would be the slowest and heaviest route of going about it.


Definitely slow, heavy, and inefficient! I like the creative thinking, though, and there have been a couple of hydrostatic drive motorcycles to prove that it can function, even if it has proven to not be a good idea.


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## skooler (Mar 26, 2011)

http://www.proteanelectric.com

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