One motor per wheel: pros/cons

[JRP3]

The quote to which you replied referenced in wheel motors, I was just differentiating the two technologies. Generally the term "wheel motor" applies to a motor contained within the wheel.

 

[thegruf]

There is one thing you can do with motor in wheel - no driveshaft so you can fully articulate the wheel!
Now that can lead to some fun manoeuvers.
Where's that NASA video clip?

 

[wallet.dat]

Multi-motor = motors can be made smaller. Smaller motors = lower possible CoG.

 

[JRP3]

That doesn't make sense. Two 30lb motors are no lighter than one 60lb motor for example.

 

[Saghost]

That doesn't make sense. Two 30lb motors are no lighter than one 60lb motor for example.

Not lighter, no. But if the 60 lbs motor is 8 inches in diameter and the two thirty pound motors are each six inches in diameter, that 60 pounds can be an inch closer to the pavement for the same ground clearance, which is what I think he meant...
Walter

 

[lklundin]

(mod note: split from Multi-gear EVs are probably the future)


One motor per wheel is desirable for a bunch of other reasons, both traction and stability/handling benefit greatly from being able to independently apply arbitrary amounts of torque to each wheel. All the serious EV supercars are doing it already, and I rather expect that it'll become either standard or an upgrade option on higher class EVs in the future - possibly even on all of them.

Apart from the already mentioned advantages of one motor per wheel, I suspect there is also potential for a reduction in weight.

A mechanical differential is heavy and more so for an axle that has to handle a large torque, such as that on the (rear axle of the) Model S.

How much do the current, mechanical differentials on the (dual motor) Model S weigh?

Or to phrase it differently, how much would the weight be reduced if Tesla Motors modified a current Model S P90D to use four half-shafts, each with its own motor and reduction gear (preserving the current rear/front axle power) ?

I think that would make for an even more interesting EV.

Thanks.

 

[jkn]

Apart from the already mentioned advantages of one motor per wheel, I suspect there is also potential for a reduction in weight.

A mechanical differential is heavy and more so for an axle that has to handle a large torque, such as that on the (rear axle of the) Model S.

How much do the current, mechanical differentials on the (dual motor) Model S weigh?

Or to phrase it differently, how much would the weight be reduced if Tesla Motors modified a current Model S P90D to use four half-shafts, each with its own motor and reduction gear (preserving the current rear/front axle power) ?

I think that would make for an even more interesting EV.

Thanks.

Not much weight saving, since differential is also part of reduction gear. I agree: 4 motors would be better than two, but not much. Perhaps sport M3 will have 4 motors.

Since I mentioned Toroidion earlier: I haven't seen measured performance numbers. It is a racing car with 4 very noisy electric motors! They plan to participate Le Mans 2017. They will be taking orders next spring. There is a video of it driving, but not very fast. -> waste of time.

 

[Oldbateryman]

I'm not a suspension expert by any means, but what I've read is that a pound on the lower side of the suspension has the same effect on handling and bumps as three pounds on the upper side.

Once the motors get light/powerful enough, that might be traded against other traits for a better overall result - and with sufficiently reliable motors that have the torque to burn rubber on all four wheels, you could in principle eliminate the brake system and its weight (need some sort of a solution for energy beyond what the battery can take; locomotive style "dynamic braking" resistance/radiators is a possibility - with a little creativity, the HVAC system can probably dump power overboard at need by heating coolant as if for the cabin and sending the hot coolant to the radiators up front instead though it can't handle the surge power levels, so you'd need either an ultracapacitor stack or to hold some battery space for panic stops and dump it if needed.)
Walter

Unsprung wheel weight makes wheel motors unworkable, race cars do not have diskbrakes on the wheel adding to there weight,, there inboard, Major handeling issues.

 

[arnis]

Rivian R1T will have one motor per wheel. But motors are not in the hub to keep unsprung weight under control.
Offroad capability will be as good as it theoretically can be.
Extremely absurd things could be done, like turning with no radius

 

[SageBrush]

Extremely absurd things could be done, like turning with no radius

Perpendicular instead of parallel parking ?

 

[HeatproofGenie]

Perpendicular instead of parallel parking ?

That would need four wheel steering. Above example or idea could only be done on loose or slippery surfaces.

I do think four motor systems could be amazing for off road implementations but race cars as well.

 

[arnis]

When left tires rotate forward and right tires backwards, we get some awesomeness.
In extreme wilderness it might be handy feature.

 

[bxr140]

I do think four motor systems could be amazing for off road implementations...

I’ve always thought a crawler with hub motors and multi-direction suspension would be the beans...

 

[dane a]

Agreed, 1 is good, 2 is better, 4 is best,.......