although it’s actually more like an ultrasonic scan.
Slightly off-topic, but there was a comment conversation about whether ESC PWM input pulse width ratio was linear wrt output motors RPM.
I used the Audio Spectrum Analyzer app, combined with running tests at various PWM speeds. Oh, and some Blue-Tak to keep Phoebe on the floor as she went over take-off speed.
Here’s what you get – make of it what you will, but it’s definitely not linear – although there are linear sections – the samples are at 5% PWM intervals and it is linear between 20 and 25%, 25 and 45% and finally between 45% and at least 60%. I daren’t take the test further just in case the blue-tak let go and she whizzed up to the ceiling. So the ESC microcontroller is doing some sort of logarithmic approximation – also not shown on the graph is that the motors RPM climbs steadily up to the PWM spin rate; the ESC is playing a role there to soften changes in desire spin rate. I’m guessing the non-linearity of the ESC is to adjust / compensate for non-linearity of the power delivered by each blade for a given rotation speed.:
I guess if I have time to kill another day, I could attach my iPad iMSO digital ‘scope and see what the ESC output PWM looks like – but, as I say, that’s for another quiet day. Now back to PID tuning, where depending on the weather, the next steps are to rerun the Z-N PID tuning with a better (nearer centre of gravity) hang of Phoebe, or a test flight with a lot lower Ki gain.