Intricancies of 2+ motors

pengyou

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I have read a number of posts here about 2 motors on a 2 wheeled vehicle. My questions here are about a 4 wheeled vehicle.

The Tesla pick-up has something like 3 motors up front and 4 in the back, give or take. I would like to convert a small 4x4 vehicle like a Suzuki Tracker. If I could put one motor in the rear and one in the front, I could eliminate the driveshaft and have more room under the vehicle for storage. I think, the area that the driveshaft takes up would be ideal for storing batteries because it would be about the center of the vehicle. Search showed me a lot of people using multiple motors. I have some questions about the implementation of this: do 2 motors need 2 controllers? Or one controller designed to controller two motors? Can a switch be mounted for the driver to use the front, the rear or both? Can electric motors be mounted directly to the differential or is it better for them to have a driveshaft, even a short one? A motor from a Leaf has about the same specs as the original in the Suzuki, but more torque - always better in a 4x4. Two motors would be overkill...but fun!
 
I think either you have some fundamental misunderstanding, or I am not understanding your communication.
The Cybertruck (Tesla pickup) does not exist yet. It is being offered for preorder with 1, 2, or 3 motors. 1 motor is rear wheel drive only, through a differential. 2 motor is front wheel drive through a differential and rear wheel drive through a second differential. 3 motor is front wheel drive through a differential, and each rear wheel driven by its own motor, no rear differential. In the trimotor, the space normally taken by the differential and axle housing is occupied by the additional motor and its independent geartrain. There might be some space between the motors where batteries could go (ordinary humans haven't seen it yet), but that is an area of very high electrical noise. Vehicle suspension is better suited by putting the rear motors as close together as possible to maximise axle length and minimize CV joint angle at full stuff and full droop.

If you use 1 motor for the front and 1 for the rear, you require 2 differentials. Splitting power from one input to 2 wheels is the reason differentials exist. Perhaps you were thinking about a center differential, or transfer case in the center of the vehicle which splits power from one engine to 2 axle differentials. Each axle differential then splits the power again between the 2 wheels it is attached to. The space that would be occupied by a transfer case, 2 driveshafts and exhaust IS the space under the seats which Tesla and other manufacturers of "skateboard" type chassis use to hold battery packs.

"do 2 motors need 2 controllers?" Yes.

"Or one controller designed to controller two motors?" That would work too, but it is essentially the same thing as 2 controllers in a single box.

"Can a switch be mounted for the driver to use the front, the rear or both?" Yes. But it would not work the way you think it would. With a motor connected and spinning, because the wheels are turning, but not powered, it represents drag on forward motion that must be overcome by the second motor. That reduces the amount of ground traction available and could result in a skid in some situations. ACIM have less traction drag when off, but some still exists, which could be mitigated entirely by simply driving both motors at a lower current. If you are paying the weight penalty to have the motor onboard, it always makes sense to use it unless a specific traction situation (like being towed) requires it to freewheel.

"Can electric motors be mounted directly to the differential or is it better for them to have a driveshaft, even a short one?" If you require a differential, it is better to have the electric motor coupled directly to it without a driveshaft. Setups like this are available at very reasonable prices from China where they are used in small rickshaws and delivery trucks. It would suit your Sammy, and leave the open space where the transfer case was for batteries.

"A motor from a Leaf has about the same specs as the original in the Suzuki, but more torque - always better in a 4x4. Two motors would be overkill...but fun!" That sounds fun to me. A vehicle I would like to drive. Good luck!
 
Thank you! Sorry for the mistake. I meant, eliminate the drive shaft. Yes, I am still looking at a differential for each pair of wheels, with one motor attached to each differential. I have read on other forums that 2 controllers in the same vehicle need some way to be managed together, perhaps some other electronic device. Do you have any knowledge about that?
 
In most cases 2 controllers can receive the same signal. Even if they drive opposite sides of the car and wheels are forced to travel at different speeds around a corner it is not a problem. Some slip is allowed. You may choose to control motors individually if you have a compelling desire for something complicated like torque vectoring, but the difference is minimal and only there at all at the very edge of traction. Just split the throttle signal and ground reference to both controllers.
 
Sorry for hijacking this thread, but what about doing 4WD by having 4 hub motors? Granted, only for a small vehicle, but any reason why I shouldn't try this for a, let's say, the classic Fiat 500?
 
by FilipK » Sep 19 2021 2:54am

Sorry for hijacking this thread, but what about doing 4WD by having 4 hub motors? Granted, only for a small vehicle, but any reason why I shouldn't try this for a, let's say, the classic Fiat 500?

High speed and for best handling you want to keep your unsprung weight down. This is why you don't see factory cars/trucks with hub motors. Hub motors are doable to lower speed EV's that would not need the best suspension.
 
Hm, not sure if I understood you correctly, but it sounds that for a classic car, where I am aiming to keep the performance the same, it might be a suitable solution? From reading on QS, you can still reach 100kph, which is a respectable speed for a Fiat 500.
 
FilipK said:
Hm, not sure if I understood you correctly, but it sounds that for a classic car, where I am aiming to keep the performance the same, it might be a suitable solution? From reading on QS, you can still reach 100kph, which is a respectable speed for a Fiat 500.

Read up on "unsprung mass" to figure out why in-wheel motors won't work well, and why EVs with one wheel per motor are likely to feature articulated axle shafts.

I reckon tiny cars with donut wheels are even more dependent on good suspension qualities than cars with taller wheels and higher mass.
 
Ok, I get that - so it's not so much driven by the performance of the motor, more by the comfort of the ride.

Is the difference really that big - the motors would only need to be 2-3kW each, and we get rid of other components that would normally be unsprung on an ICE car. This is a genuine question as I've got no feel on the impact a slight (however vague that is) increase in unsprung mass would have on ride comfort.
 
FilipK said:
Ok, I get that - so it's not so much driven by the performance of the motor, more by the comfort of the ride.

Not just comfort, but traction and safety. The more unsprung mass, the more often the wheels lose contact with the ground.

I guess you'll need to find a candidate motor and wheel to compare its weight against the weight of the parts to be replaced.
 
You can read about all the bikes here with hub motors, they go bike speeds. As soon as you move up to motorcycles and much faster speeds they move the motor from the wheel to a mid mount. This transfers the unsprung weight to the chassis.

There is the exceptions of the big hub motors but you need to understand the trade offs before investing.

When wheels run across holes the suspension needs to react as the keep the chassis as stable as possible so you can remain in control. When the suspension does not perform well you will feel a loss of control. Grant you there is more to suspension than unsprung weight.

It's not that you can not do it. It's a low speed design and must be treated as such.
 
FilipK said:
and we get rid of other components that would normally be unsprung on an ICE car. ......
What components exactly do you believe you could “get rid of” ?
On a car with independent suspension like the Fiat 500 etc, there is little that can be removed, unless you think you could dispose of brake rotors calipers etc. But i am not aware of any EV that has done that yet,....or if it would be legal ?
 
Hillhater said:
FilipK said:
and we get rid of other components that would normally be unsprung on an ICE car. ......
What components exactly do you believe you could “get rid of” ?
On a car with independent suspension like the Fiat 500 etc, there is little that can be removed, unless you think you could dispose of brake rotors calipers etc. But i am not aware of any EV that has done that yet,....or if it would be legal ?

To be fair, you have to ditch the stock hubs if you're going to use hub motors. That probably means ditching the brakes too, at least in their original form. Substituting ATV brakes or whatever else can be made to fit might reduce the weight some.
 
https://www.diyelectriccar.com/threads/my-1986-suzuki-samurai-re-conversion.184017/
Probably best to do a traditional motor to transmission setup using one big motor, dilemma being the motors length and the space inside the engine compartment, they are pretty small suv's.
Suzuki Sidekicks and Geo Trackers have pretty amazing gearing, you can gear them so low and you'd be able to crawl up the tourist attraction called Everest, a summit where 8000 people have been.

I wouldnt bother with the electric axles (links + picture below) any half ass serious off roading, you need Toyota axles, or Ford 8.8 (slightly stronger then D44, dont go for the C-clip models) or D44 but the ifs of the Zukes can be made stout or go s.a.s.

Besides all that work, the 1.6L Suzuki Sidekicks / Geo Trackers get pretty amazing fuel mileage as it is.
You convert to propane and they get even better fuel mileage.
Then start doing exotic setups with sprayers or do a diesel swap and your kicking ass and taking names. Cant hit a mud hole or dunk in water with an EV.

All depends on what you want to do with your Zuki


https://www.goldenmotor.com/
https://www.goldenmotor.com/eCar/gearbridge18%20tooth.jpg

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For smaller slower moving vehicles multiple hub motors are probably fine.

Like if you are making a UTV or golf cart type vehicle.

The advantage to them is you can keep the suspension simple and have a wide open flat floor. Also keep the center of balance very low to improve stability on inclines. Like if you want to maximize passenger space or have a relatively low and wide platform for loading and unloading cargo.

Would be great for small offroad vehicle, agricultural vehicle, industrial vehicle, campus vehicle, etc etc. Things people use micro trucks, gators, and golf carts now.

I wouldn't want them as any sort of electric car or car replacement vehicle that is expected to safely and comfortably drive highway speeds.

As far as the complexities go... As long as all the motors and wheels are identical then you can just feed them all a shared throttle signal and they should be fine.

If you want to take advantage of the 4 wheel motor stuff... like being able to do things like make zero-radius turns like a bulldozer or zero-turn lawn mowor then you'll probably want to invest in some sort of micro-controller to manage the throttle signals to each wheel independently.

In terms of performance you are generally going to be always better off with 1 or two bigger motors then 4 smaller ones. Just depends on where/how you can fit the bigger motors and such things.

If I was converting a small car I would probably use the approach of using a Nissian leaf motor and use drive shaft adapters to the factor hub assembly.
 
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