Quote:
Originally Posted by MPaulHolmes
I don't think the problem is lack of resolution. The problem is that it's perfectly fine (according to the throttle-power scenario) at zero rpm for the current to go to 500 if the duty is very small, since all that matters is the product of current and duty. There would be no reason in the throttle proportional to power scenario to keep one extreme from happening when the other is the opposite (huge current, tiny pwmDuty or tiny current, huge pwmDuty for tiny throttle). It wouldn't know to make current smaller, since the product would be small.
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Yes I think I see your point now, and I am realizing that what we perceive as power is not the same as the actual power being delivered. what we perceive as power is really just thrust or the torque applied at the drive wheels; so motor torque / gear ratio / final drive ratio. Real power is exactly what your equation is, so at 0 or low RPM you are getting all torque to reach the requested power level and you get that kick in the ass as soon as you step on the throttle even lightly, then the torque drops off rapidly once the motor starts turning and generating back EMF.
I don't know if you have logged your current / PWM with this formula, but I doubt that you were actually getting 500 A at PWM of 1 other wise all of your other formulas would also have low throttle problems as well.; as I was saying before if your PWM is already at 1 then your program will be unable to get the current any lower, so the problem must be in the handling of that PWM value. as you stated at low RPM the power can remain low even with high amperage so with a low throttle setting you may initially get a PWM of 1, but because the the formula calculates this as not enough power it quickly increases PWM to get that power, and current goes excessive. you may even be getting oscillations depending on the reaction times of the code and hardware.
In short I think that you are correct that throttle = power is not the correct method, but I am writing all of this because I think that the hyperbola graph I showed you is still relevant applied to PWM, but use it with your formula for throttle = current instead of throttle = power. this will give your program better ability to control the current at low RPM.