Arlo1 wrote:Stock colossus has 8uh! What we need is to wind it to 35kv and terminate it in WYE! I worked all the numbers and it will work out to be 10 turns a tooth and 106uH inductance
Rewinding the motor to get higher inductance will not help, unless you plan to keep the same battery voltage as before the rewind (and get less power in the process).
If you double the amount of winding turns, the inductance will get 4 times higher, and the kV will be halfed. 4 times more inductance will lower rise rate in windings by a factor of 4, and I guess that is what you seek. However, when you double battery voltage to get the same RPM as before the rewind, then you double the rise rate, which will put you at half of what the rise rate initially was. Further, with a halfed kV, the peak current will be halved. So, if the peak current is halfed, and the rise rate is halfed, then the rise time will be the same as it originally was.
If you want to lower the rise time (EDIT, I mean increase rise time / lower rise rate), you could just lower battery voltage, it will have the exact same effect as rewinding the motor without changing battery.
Adding external inductance will not help you get to 50kW either IMO, because that added inductance will prevent currents to rise fast enough to get much torque at high RPM.
I once read about a controller for an ironless motor. It had little different approach compared to the common BLDC controllers. It used the 3-phase bridge only to commutate the machine. Then there was also a PWM stage similar to a brushed DC controller. And in between them there was an inductor. So, it was a high power Buck-converter followed by a 3-phase bridge.
I think the normal hardware approach will do though. I think it's a matter of software. My thought is that the software needs to drive the motor with a waveform which corresponds to the EMF of the motor. If the motor is driven with a constant PWM, then I think the current will spike near the end of every commutation step. When the EMF passes the peak and starts to fall, then the difference between EMF and battery voltage will rise, and the current will then rise too. This is just a theory, and I have no experience in making brushless controllers, but I do have some experience with switched inductors.