Thread: Discussion ESC update frequency
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Old Sep 12, 2011, 05:48 PM
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ESC update frequency

I have seen it stated many times that 400 Hz is a desirable update frequency and that 200 Hz is borderline unstable.

Can someone point me to testing that can support this? I am skeptical because of the basic physics of accelerating and decelerating the air mass out of the propeller. I doubt you can influence it that quickly, after all a propeller is not a speaker.

For example a 6000 rpm prop is spinning at 100 Hz. With a 400Hz update you are trying to change the rpm every 1/4 revolution. I find it hard to believe that any significant acceleration or deceleration can happen in 1/4 revolution, 2.5 milliseconds.

A typical prop weighs 20 - 25 grams. It is spinning at 6000 rpm therefore it has a certain angular momentum and it seems hard to believe it can slow down or speed up any significant amount in 1/4 turn. After all the prop has to change it's velocity enough to change the amount of air it is pushing down. This means the thrust needs to change. How much? I don't know.

Here is a plot from my eagle tree logger collected at 50 Hz. That is not fast enough to capture 200+ hz activity but it shows very little prop rpm change over this 1/2 second. An interesting bit is the watts shows a lot of activity over the same period. I don't know if that is noise/ ripples in the power or what.
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