HW 100A v3 - Re-do Gov Store calibration after changing PWM setting?

[The Tok'ra]

Hey guys,

Ive got a HW 100A v3 on a G500 sport with a XNova 4020 1200Kv motor.

I've been running the ESC on the default settings of 15° timing and 32kHz PWM, but I have noticed that the ESC is getting a bit too warm to touch after each flight.

I will change the PWM from 32kHz to either 24kHz or 16kHz so the ESC will run cooler, but when I've done that, do I need to re-calibrate the gov store again? i.e. RPM standardization, or perhaps changing the PWM frequency does not require re- calibration?

Thanks!

[The Tok'ra]

I asked the same question over on HF, and the answer from Darksyd3D (HW Support) is NO, you do not need to re-do Gov Store RPM Standardization when just changing the PWM frequency.

Hopefully this thread can help anybody else who has the same or similar question.

[Crashalotjoe]

The PWM (Pulse Width Modulation) value changes the duration of the pulses driving the motor. It doesn't change the frequency of the pulses so the motor speed does not change.

As above: there should be no need to adjust the governor.

[Grumpy]

The PWM (Pulse Width Modulation) value changes the duration of the pulses driving the motor. It doesn't change the frequency of the pulses so the motor speed does not change.

As above: there should be no need to adjust the governor.

Actually no, the PWM setting that you adjust in the ESC does change the frequency, that's why the adjustments are in units of frequency (KHz). But you are right that PWM frequency doesn't effect motor speed. Motor speed is dictated by the duty cycle (% of time that the pulse is on vs off) which is controlled by throttle.

[The Tok'ra]

Just wondering, does anybody know if reducing the PWM frequency from say 32kHz to 16kHz is likely to have a noticeable difference is ESC temperature, assuming no other parameters are changed, and the gearing stays the same? I'm currently using the stock 18T pulley on my G500, and 75% throttle in Gov Store mode, I realize this is not optimal, and a 17T pulley and a higher % throttle curve would probably be a better choice for the HS I'm running.

[Grumpy]

As you say, slightly lower gearing and higher % throttle curve would be the much better option, but yes, running lower PWM frequency should reduce ESC temperature at the possible expense of a bit more heat in the motor.

[Crashalotjoe]

Actually no, the PWM setting that you adjust in the ESC does change the frequency, that's why the adjustments are in units of frequency (KHz). But you are right that PWM frequency doesn't effect motor speed. Motor speed is dictated by the duty cycle (% of time that the pulse is on vs off) which is controlled by throttle.

Interesting. I thought the PWM pulses were made up from a string of pulses followed by a period of 0v followed by the string of pulses again and so on. The duty cycle is the frequency of the +ve pulse string vs the 0v portion of the signal and so changing frequencies via the throttle drives the motor at different speeds. Changing the frequency of the PWM signal changes the pulse width of the pulses in the +ve part of the cycle and so has no effect on the motor speed but changes the effective power levels applied to the motor. Obviously changing the pulse width changes the PWM frequency (hence why it's quoted in kHz) but it's not the 'mark/gap' frequency that is driving the motor speed.

I have to say; if you can make head or tail of what I just wrote you are a better man than me (or maybe you've just consumed a similar amount of whiskey) .

[Grumpy]

PWM is just a series on on off pulses. The length of time the pulses are 'on' vs the length of the 'off' period determines how much power the ESC puts out, AKA 'the duty cycle':

Read all about it: https://www.arduino.cc/en/Tutorial/PWM

[Crashalotjoe]

PWM is just a series on on off pulses, all equally spaced. The length of the 'on' pulse vs the length of the 'off' period determines how much power the ESC puts out, AKA 'the duty cycle':

Read all about it: https://www.arduino.cc/en/Tutorial/PWM

Yes, I know about PWM but the motor drives are not that simple. As far as I can find out, the drive is a string of PWM followed by a period of no PWM followed by more PWM pulses. It's the gap between one string of PWM and the next that defines the drive frequency and therefore the motor speed. The frequency of the PWM itself defines the power delivered to the motor. At least, that's how I understand it.

[Grumpy]

Yes an ESC is more complex but the PWM part is just as I described. What you also have on an ESC superimposed over the background PWM signal is the commutation frequency as the ESC switches between positive and negative as it energises the motor coils. So what you have is a series of positive PWM pulses followed by a series of negative pulses, but the +/- commutation frequency is governed by the RPM and pole count of the motor and is nothing to do with the PWM frequency that you set in the ESC.

[The Tok'ra]

Good info there, thanks guys!!

[Grumpy]

So this is what the ESC signal looks like. The short on/off pulses is the PWM signal and the sine wave like positive to negative wave is the commutation frequency. The PWM switching frequency (as set in the ESC) should always be considerably higher than the commutation frequency (about 3x or more)

[The Tok'ra]

Nice!! Thanks for posting that Grumpy, very interesting!