Servoless RC undercarriage retracts connecting to Duet 3

becky9 · 15 Feb 2021, 13:31

https://www.flyingtech.co.uk//electronics/servoless-retract-metal-trunnion-diy-landing-gear

I've had the idea to use one of these to flip out a brush to clear nozzles, they can run off 5v and are fairly inexpensive. They run 3 wires, presumably Power,GND & a control signal. I'm hoping I can hook up to an external 5v source with a common ground with the Duet and run the control from an IO pin?

Does this sound ok?

x

Phaedrux · 15 Feb 2021, 18:17

If it accepts a servo signal it should be similar to connecting any other servo and control with M280 or M42

becky9 · 17 Feb 2021, 09:55

Thanks @Phaedrux its supposed to accept a servo signal. I can get a normal servo working but when I swap it out with the Retract it doesn't do anything. Its designed to fit onto an RC channel with a 2 position switch, and I expected beyond particular values for it to trigger.... will have to play some more! x

DIY-O-Sphere · 17 Feb 2021, 10:52

@becky9
Smart idea, but I would choose a more stable version. link
The alignment with the 4mm pin is not that easy.
In the linked variant you could also cut threads in the trunnion to mount a plate.
Would like to see your design.

becky9 · 17 Feb 2021, 12:23

Thanks @DIY-O-Sphere that does look better, as soon as I get it working I'll order one of those. I don't have a design yet, but I'm going to bolt it to something similar to Gregs Adjustable Cleaning brush. Unfortuately I don't have the space to run Gregs as it is and will need a swing arm. Currently I have a stepper bolted to a mount, which bolts to a piece of extrusion which has a short piece of rail, and a leadscrew on the stepper. Just need to design and print the carriage, which will depend on whether I actually use the RC Retract thingie x

becky9 · 17 Feb 2021, 12:25

by Gregs, I meant Greg from E3D, https://www.thingiverse.com/thing:3744969

becky9 · 18 Feb 2021, 09:18

Just as a follow up to this, it is now working.

This being my first foray into servos through the Duet, I hadn't realised that values with M280 beyond 544 were pulse widths.

simply ran a loop sending increasing pulse widths every second from 544, broke in down into chunks, so did 300 at a time, until something happened, then narrowed it down from there...

To extend the leg, the window was 666 to 1200, so 900 works well.

To retract the leg, the window was 1740 to 2300, so 2000 works well.

Oh yes before I forget, I'm running this off OUT9, which I understand has 5v pwm, not sure if it works off the other ports as I haven't tried it.

Happy happy! x

DIY-O-Sphere · 18 Feb 2021, 10:32

@becky9
For the final version you should supply the servo by an external power source.
The internal source supports only small servos.
Only the signal line is needed.

becky9 · 18 Feb 2021, 11:01

@DIY-O-Sphere I'm ahead of you, it was always running off an external psu, but thanks