Can somebody explain me teh difference between the modes you can select in the PPM mapping and when to choose one more to the other, or point me to where I can find the discussion on that topic. I am using a Trampa VESC to control a foil board motor, which mode will fit the best and why (definitely no brake needed...)
Current control - controls the current to the motor and consequently the torque, it gives torque control (acceleration) but does not limit or try to control the speed.
Duty cycle control - controls the duty cycle (voltage) to the motor and consequently the speed, it gives rough speed control (velocity) but does not control the current (the maximum set motor current will be used to accelerate or decelerate the motor to the commanded duty cycle). Will not increase the duty cycle to maintain the same speed when under heavy load.
PID speed control - controls the ERPM (velocity) of the motor, tries to always make the motor turn at the commanded speed irrespective of the load. Duty cycle and current will change to maintain set ERPM. Requires tuning for best performance.
For your use case of efoil, current control will change your acceleration, duty cycle will control your speed (but acceleration can be very harsh), PID will act similar to duty cycle.
So I would either use current control, or duty cycle with the positive ramping time in the PPM page set to something reasonably high to limit the acceleration, (at least while you get used to it)
Thanks for the clear explanation. Yes current seems the way to go for my application.
trom
Actually, using the current set up, I reach the max phase current my motor can handle (100amp) at about 50% duty and therefore only a power of 2 kW with an input current around 45Amp, so I guess a phase voltage about 20V. Would a duty cycle program with a max current of 100amp allow me to get about 4.5kW at 100% duty (with the full 12S voltage of 45V?)
trom
If you are hitting the current limit before 100% duty cycle then your not gearing down the motor enough for you load. Try adding some more mechanical reduction, smaller pinion, pulley, gear etc.
Thanks a lot for the answer but it is on an efoil, I guess I can try to change the propeller pitch (though it will reduce the max speed).
But I am a bit surprised that the VESC can't be tuned up to fit better the actual spec of the motor/gear/prop assembly. I am using the Trampa VESC6.4 rated at 80 amp continuous with 12 S battery, the motor max current detected is 100amp so it should fit quite well...
trom
It doesn't work like that, the load will always determine the torque required from the motor at a given speed. If you can't accelerate past a certain speed with the current pitch, change to a lower pitch and you will get better acceleration and probably a higher top speed as well.
Old thread, but on the efoil use case:
Before you are on foil you are pushing a lot of water so the load is way higher. I have my throttle set to current control with ~120-150A max, I can easily hit that before I'm on foil. After on foil, I'll top out my duty cycle way before current (maybe at like 60A). Attempted to use duty cycle mode, but something wasn't configured correctly and it didn't work well. Maybe PID speed control would be better yet, but haven't had to to experiment with that yet.
Same thing could happen with a skateboard with a changing load, going up a steep hill (max out current) vs going down a hill(max out duty cycle), but probably not as dramatic unless you had a extremely torquey setup.