shutting down a servo?

jay_s_uk

@Tinchus the servo will always have power unless you switch that power off. you would need a relay to do so

droftarts

@Tinchus Strange, it works for me, I've just tested it. I sent:
M280 P0 S100 > servo moves to 100 degrees
M42 P0 S0 > servo 'turns off', can be moved manually

M280 P0 S100 > servo moves to 100 degrees
M280 P0 S10 > servo moves to 10 degrees
M280 P0 S5 > servo tries to move to 5 degrees, but stalls, with noise
M42 P0 S0 > servo 'turns off', noise stops, can be moved manually

My servo is a Hitec HS-70MG 12.5g.

Ian

Tinchus

@jay_s_uk ok. My intentio is not to cut the power" but to achieve what in the documentatios is refered as away to avoid having the servo in a stall situation.
lets forget about the noise, if I execute m42 P0 S0 even if I have the noise I can trust no control signal is being sent to the servo?

Tinchus

@droftarts I remember having tried that servo, I changed it just becauso of it torque (the futaba one is almost double). And the other important differentce is that your servo is analog, mine is digital

droftarts

@Tinchus I think if you still hear noise, it's still trying to get to position, so still stalling. If M42 isn't working, maybe digital servos need a different mechanism to turn off. I've asked @dc42. Is there any information on this in the futaba SU-300 data sheet?

Ian

o_lampe

A humming servo is a regular thing, when it doesn't reach the desired angle.
It happens, even when the servo arm is within the boundaries of the internal gears, but it's no problem then. (unless your setup requires too much torque)
You could try one thing, for peace of mind:

command the servo 5 degree or microsecond past the point you want to reach (whichever you prefer)
wait a little while for the arm to reach the position (eg. G4 P200 ; waits 200milliseconds)
move 5 back

With that trick, you'll overcome the backlash of the internal potmeter and it will be quiet
Maybe have to adapt to different angles/microseconds for your specific servo

zapta

@Tinchus, I have a non Duet project where a servo needs to be quiet between moves and I solved it by stopping the signal to the servo (PWM output stays at zero volts) instead of pulsating. Potentially you can do the same with the Duet. E.g. by reconfiguring the IO point.

achrn

@Tinchus your problems might be your choice of servo.

Futaba SU300 is a digital servo. It doesn't want to see PWM, it wants to see SBUS, which is serial data, 25 byte packets, at 100,000 baud, and the polarity is inverted.

I think that if it doesn't get SBUS, it 'falls back' to looking for 'normal' servo PWM, which is why it works at all.

I suspect (but this is speculation) that M42 doesn't work as expected because when the servo doesn't see either SBUS or PWM it holds position. Possibly you can program what it does in that situation if you put it on a programmer (you want a CIU-3 programmer, I believe), but that's about 50 quid. I'd buy a 'normal' PWM servo instead.

Alternatively, there's a reasonably straightforward SBUS arduino library by Bolder Flight Systems - possibly you could lash together something where your Duet talks to an arduino and the arduino talks to the servo. Still, I'd buy a 'normal' PWM servo instead.

Tinchus

@achrn I think you nare oin the righht truck. I was suspecting something about this and ttalking to futaba support about it. I will try to get a non pwm servo, any recommendations about it?

droftarts

@Tinchus You may be able to get the Duet to send the correct SBUS commands, similar to how @DonStauffer did it with the NeoDriver LED board: https://forum.duet3d.com/topic/35384/neopixel-driver-results

Ian