Hi -

On my 5" quad I set my PWM low to 16 khz and PWM high to byRPM (running 32.9 blheli32). When the low is set to 16khz and I arm the quad I get a fluttering noise from the motors. It flies fine when I take off and performance is good but I was wondering about the sound. The fluttering sound goes away when I move PWM low to 24khz and leave PWM high at byRPM.

Any ideas?

Thanks!

I personally never go lower than 24khz for the low pwm settings and on 5” motors you have enough torque.

Going any lower is something I have not tested but it should be a function of the motor build/design/quality and the MOSFETs used on the ESC.

I am sure most MOSFETs will be able to handle the lower pwm range since it means less switching off/on cycle (in layman’s terms) but components can behave differently when part of a circuit.

Im not going to technically dive into this much but an article like this will explain some basics: https://www.4qd.co.uk/docs/what-is-pwm/

Based on what I have read on rcgroups and github around BLHeli, the devs usually mention that the min/max PWM limits of an ESC is usually decided by the manufacturer. However I am not completely certain if they just come up with such ranges or have actual tests to backup their specifications.

If someone wants more objective comparison then a motor test stand will be great to justify the behaviours based on measured data rather than just “sound or feel”. Personally even if I can afford buying a motor test stand, I can’t justify owning one for the rare use it will get.

(13-Aug-2022, 02:51 AM)kafie1980 Wrote: I personally never go lower than 24khz for the low pwm settings and on 5” motors you have enough torque.

Going any lower is something I have not tested but it should be a function of the motor build/design/quality and the MOSFETs used on the ESC.

I am sure most MOSFETs will be able to handle the lower pwm range since it means less switching off/on cycle (in layman’s terms) but components can behave differently when part of a circuit.

Im not going to technically dive into this much but an article like this will explain some basics: https://www.4qd.co.uk/docs/what-is-pwm/

Based on what I have read on rcgroups and github around BLHeli, the devs usually mention that the min/max PWM limits of an ESC is usually decided by the manufacturer. However I am not completely certain if they just come up with such ranges or have actual tests to backup their specifications.

If someone wants more objective comparison then a motor test stand will be great to justify the behaviours based on measured data rather than just “sound or feel”. Personally even if I can afford buying a motor test stand, I can’t justify owning one for the rare use it will get.

Interesting. I guess I'll just go to 24khz for the low. Don't think it made a noticeable difference on responsiveness to me anyway.