Dual Motor Speed Control Arround Corners

[SuperV8]

Just having a think about my 'future' build and I think i'm heading towards dual motors for front and rear axles.

This got me thinking about controlling them, and couldn't see anywhere which my question is discussed.

Is the inverter controller/software able to drive two motors at different speeds depending on a signal from the steering angle sensor?

So going round a corner - front and rear axle will be turning at different speeds - can this variation in front/rear axle speed by mapped in depending on a steering angle sensor & vehicle speed?

Tom.

[CoreyS]

Tom,

I lost my original post somehow, so here is the short version.

I believe the software can drive two different motors, but you would need a ton of points to be mapped to get it to feel natural. Lots of trial and error.

The most important part is the left and right wheels will be turning at two different speeds and you want to apply more torque to the outside wheel.

You also need more input variables:
Throttle
Steering Angle
Brake
Yaw/pitch/roll
Individual wheel speed
And I'm sure I'm missing some.

I've thought about this on and off. Check out how some of the EV hypercars do it and you may be able to get some ideas!

[johu]

Not quite sure if I get your point. ONE motor in the front ONE in the back? Why would the front axle spin at a different speed then the rear axle, neglecting slip?

That said, controlling multiple inverters is a task for a VCU. The inverter just produces torque as commanded (not speed)

[arber333]

Not quite sure if I get your point. ONE motor in the front ONE in the back? Why would the front axle spin at a different speed then the rear axle, neglecting slip?

That said, controlling multiple inverters is a task for a VCU. The inverter just produces torque as commanded (not speed)

I agree. Besides, you can just use 2 different inverters if you like and use one Prius or Auris throttle with 2 channels. That way you can drive both inverters by the same throttle proportion.
https://leafdriveblog.wordpress.com/tag/throttle/
https://mazdamx3ev.wordpress.com/2016/02/12/pedal/

[Isaac96]

If the motors are the same then there should be no issue as the motor is torque controlled, not speed controlled. Even with different motors it would still work, just be painful to tune. Since you need one inverter per motor.
Left/right -- just use a torque biasing diff or something?

[SuperV8]

Not quite sure if I get your point. ONE motor in the front ONE in the back? Why would the front axle spin at a different speed then the rear axle, neglecting slip?

That said, controlling multiple inverters is a task for a VCU. The inverter just produces torque as commanded (not speed)

Yes, one motor in the front, one in the rear. (each with an open differential for LH & RH)

My thinking is that with truck 4x4's like the old Landrover Series III for example - there was no centre differential - so you could only use 4x4 when on soft/loose surfaces. I.E. the front and rear axles turn at different speeds when going round a corner.


If both axle's of an EV are driven at the same speed then when you go around a corner there would be some torque difference between axles which may compromise handling? Probably depends on how strongly each motor can match it's requested torque?

[SuperV8]

If the motors are the same then there should be no issue as the motor is torque controlled, not speed controlled. Even with different motors it would still work, just be painful to tune. Since you need one inverter per motor.
Left/right -- just use a torque biasing diff or something?

The torque biasing diff is a benefit to Left/Right on the same axle - so surly torque biasing for the front/rear axle would also be a benefit?

I see now that yes being torque controlled the front and rear axle's would be able to rotate at different speed around a corner so could work ok - but could it be optimised with different torque requests for front and rear axles? and can the dual inverter controller do this? - depending on a steering angle sensor?

[arber333]

The torque biasing diff is a benefit to Left/Right on the same axle - so surly torque biasing for the front/rear axle would also be a benefit?

I see now that yes being torque controlled the front and rear axle's would be able to rotate at different speed around a corner so could work ok - but could it be optimised with different torque requests for front and rear axles? and can the dual inverter controller do this? - depending on a steering angle sensor?

Hm... I found out that once you get an idea you think is something new, go and check if there isnt something similar out there. Usually progress is built on the shoulders of existing success.

Would a 4x4 car with ESP implemented work for you? There you have direct control of engine torque output using existing ABS sensors. You would have to find correct CAN msg that reduce torque to the engine...

On second thought i would just use a leading/main motor with larger torque, say 25% more torque on the front axis and rear motor with lower general torque that would follow the first one. Then you can use a mixer controler that will take throttle and regen inputs and distribute them between front and rear.