I agree on the separate rear motor not needing a locker. Response time will be sufficient like that without using the brake modulation for traction control.
I thought the the motor setup was the other way around with the induction being better for power but the PM motor better for efficiency?
The PM in the front was meant to make it operate in FWD in cruise for better range?
The PMSR motors are more efficient than the induction motors.
When you get into an AWD trimotor that’s cruising on the freeway at maybe five percent of rated power, it gets more complicated.
In that situation, the best case would be to have one PMSR running at fifteen or twenty percent of rated power, with the other two motors asleep and just rolling along - but you can’t put the PMSR motors to sleep, because the magnets keep on generating current.
That’s part of why Ravens have a PMSR front motor - the big induction motor in the rear is asleep 90% of the time on Performance cars, and that’s more efficient than having a bigger PMSR in the rear for them that’s running at lower power levels most of the time. (The other part being Tesla hasn’t designed a 350 kW PMSR motor core.)
So four obvious options for the Trimotor Cybertruck:
Could do induction on all three, but it’d overheat at high loads and be less efficient.
Could do PMSR front motor and induction rear motors. This is most efficient on the freeway, with the PMSR running in the mid load range and the two induction motors asleep.
Could do PMSR rear motors, and induction front. This has better track performance, but is slightly less efficient on the freeway because the two rear motors both have to stay alive, and each is operating at a lower, less efficient power level. That my guess for Plaid, and I wouldn’t be surprised if the Cybertruck trimotor copied it.
Finally, could do three PMSR motors. This option offers the best long term heavy load performance (Track driving, etc,) because all the motor rotors run cooler, but you can’t put anything to sleep on the freeway, and may even pay extra losses for through the road torque mismatches, like I suspect the AWD PM EV competition are. This is likely slightly less efficient on the freeway than the all induction solution , but I’m not 100% sure.
From what I’ve read, the PMSR motors are likely cheaper to build than the similarly sized induction motors. So it’ll be interesting to see which option Tesla chooses.
