Rc Servo For Extruder Switch

Krunder

Hello.

I just installed a Duet 2 wifi 1.04 firmware 2.05 on a dual extruder printer (Raise3D Pro2)
The printer uses a rc servo to lift / lower the nozzles.

I found and read this description: https://duet3d.dozuki.com/Wiki/Using_servos_and_controlling_unused_IO_pins

I supply the servo 5v via a buck converter.
I would like to use the PWM pin on fan2.

I send M106 P2 I-1 to disable fan2.
With M106 P2 it replys: Fan disabled.

The pwm pin in fan2 is now be called 22 right?

When I send M280 P22 S90 the servo should move to center-ish position, but nothing happens?

What am I missing?

Thanks Krunder

Phaedrux

@krunder said in Rc Servo For Extruder Switch:

The pwm pin in fan2 is now be called 22 right?

I'm not actually positive about that, but I think so. 20 = fan0, 21= fan1, 22 = fan2.

Might I suggest switching to RRF3? It's far easier to define and use pins.

M950 S0 C"fan2" ; create servo 0 on fan2 pin
M280 P0 S90 ; control servo 0

@krunder said in Rc Servo For Extruder Switch:

I would like to use the PWM pin on fan2.

Which pin are you using from Fan2? PWM is switched on the negative side.

Krunder

@phaedrux

Yes, I use the negative pin.

I stayed with RRF2 because it has worked well for me - I will take a look at RRF3 and see if it makes a difference.

Thanks Krunder

alankilian

@krunder Do you have a pullup resistor from the servo signal pin to the servo positive power pin?

Since the fan negative is a MOSFET to ground, it doesn't actually produce a signal that switches from 0Volts to 5Volts without an external pullup resistor.

I think anything anywhere in the 4-20 kilo Ohms would work.

Krunder

@alankilian

I tried 4,7K and 10K - Not working.
I will try again tomorrow at work and see what happens.

alankilian

@krunder OK, do you have the negative output of the buck converter connected to the negative of the Duet?

(Just in case it's an isolated buck converter. But I doubt it. I'm really just guessing now since you're doing everything right as far as I can tell.)

Phaedrux

Any details on the servo? Photo? Photo of the wiring? Maybe we can spot something.

Krunder

Sorted

I got it working. The pullup resistor did half the job. The other part was to reverse the signal with M280 P22 S90 I1

Being a RC pilots for many years, a reversed servo signal means that the servo moves in the other direction. This is not the case here - where I expect it reverses the pause with the output.
Here is a small sketch to help others with the same problem

Thanks for the help.
Krunder