Quote:
Originally Posted by thingstodo
I'm with Astro on this one. The differential case of going around the corner, and allowing one wheel to 'slip' is OK with the same torque setpoint to each wheel.
If one wheel loses traction, the torque setpoint will accelerate the wheel quickly. Depending on the acceleration rate, I don't know if the current will go down in an obvious way?
Maybe a limit on the difference between the frequency output for the two wheels? That would imply sharing the output frequency between the paralleled controllers.
I see a solution in having the same controller develop outputs for both AC motors - twice the calculations and twice the outputs ... but less complicated to co-ordinate? I don't like that solution but I can't come up with anything better right now.
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Not quite. Yes the wheel will accelerate, but by the time you gain traction, if nothing is done, it will kick all the mechanical inertia of the motor to the pavement. Dangerous with icy/rainy conditions.
Most new controllers can drive two motors from the same CPU with little overhead. ST has a few. Then you need to implement a differential in software. The torque is only the same if both wheels are in sync, otherwise kill torque to allow the wheel to adhere to the road again. Once they are synced apply torque again.
EDIT: Kill torque is the wrong expression:
To clarify:
Imagine two DC motors connected in series. As one wheel slips, torque will be lost, therefore the current is reduced. At this point the second motor will also loose torque as the current is shared between them. This is exactly how a mechanical differential works. So its just a case of adapting the control of the AC motor to follow the same path.