12v Servo Control 1LC Tool Board

toms

Hi!

Should it be possible to drive a 12v servo using the 1LC Tool Board? I'm powering the tool board and Duet3 Mini 5+ with a 12v power supply capable of 7 amps.
I've tried the following...

a) I originally tried running the servo off of out2 but It wouldn't move, so I figured the 0.8 amp limit wasn't sufficient to drive the servo.

b) So I tried...

The power and ground wires of the servo routed through to out0 (because of the higher amp limit 5amps) (still at 12v - Vin == 12v)
The signal wire of the servo running to out2.tach

The config I'm using is

M950 S0 C"121.out2.tach" Q250
M950 S0 C"121.out2+out2.tach" Q250 ; Doesn't work "invalid pin name"

M280 P0 S1500 ; Doesn't work, no movement, no sound from the servo
M280 P0 S45   ; Doesn't work, no movement, no sound from the servo

I've tried the same set up using out2 as well (instead of out2.tach)

The tool boards CAN address is the default 121 and I can communicate with the tool board, M115 B121 and M122 B121 commands return results as expected.

The servo's manual claims that the signal line can operate between 50-330Hz, and the operating voltage is between DC8.4V~12.6V.

I feel like I might be over looking something simple here. Any help would be greatly appreciated!

droftarts

@toms I think there are a few things wrong
.
First, wiring. The positive and negative wires of the servo need to be connected to +12V and GND on your separate 12V PSU. Make sure the GND of this PSU is connected to the GND of the PSU that supplies the 1LC. See the image on the servo main page to identify the wires.

The signal wire needs to be connected to a PWM-capable pin; out2.tach is a digital input pin, not a PWM output pin. OUT_0, OUT_1 and OUT_2 (VIN signalling, 12V maximum for this servo ) or IO_0 (3.3V signalling) can be used. However, I can't see what the signal voltage should be from the servo specification; usually 3.3V is okay.

Next, configuration. Assuming you are using 121.out2 for the signal wire, send M950 S0 C"121.out2" Q250. The frequency set by M950 Q250 (250 Hz) is within the range of the specifications (30-330Hz). The pulse width you send with M280 must be between 500 to 2500 uSec, so don't send S45; you may damage the servo.

For more info and recommendations, see https://docs.duet3d.com/en/User_manual/Connecting_hardware/Motors_servos

Ian

toms

Hey @droftarts

Thanks for clarifying that out2.tach is an input pin, I saw three pins and just assumed it was power, ground and signal.

I think it ended up being a signaling voltage issue! I tried switching the signal wire over to io0.out like you suggested and it worked! So I guess the servo wasn't responding to 12v PWM signals.

toms

The current set up that's working now...

12v power supplied to the 1LC Tool Board
Power and ground wires of the servo running to out0 power and ground screw terminal
Signal wire running to io0.out

The reason for the power and ground routed through out0 is due to only having a single power and ground line running from the main board to the tool board. I guess I could splice the power lines at Vin but using out0 lets me cut power to the servo using the M42 P0 S0 command.

The config.g file

G4 S2                       ; wait for expansion boards to start
M950 P0 C"121.out0"         ; out0 5amps @ Vin (which is 12 volts in our case)
M950 S1 C"121.io0.out" Q250 ; io0.out 5v PWM capable, Q = 250Hz PWM Frequency

Interacting with the servo

M42 P0 S255   ; Supplies the Servo with 12v

M280 P1 S600  ; Moves the servo to lowest position
M280 P1 S2500 ; Moves the servo to highest position

M42 P0 S0     ; Turns the servo off

I know this probably isn't the intended use case for the 1LC Tool Board but it seems to be working.

Thanks for the help, I really appreciate it!

dc42

@toms with that wiring configuration there is a danger that you will feed 12V into the io0.out pin when the tool board is powered up. You should connect the servo negative supply wire to ground instead. The 4-pin output connector OUT1 has both +VIN and ground connections if you fit the VOUT jumper.

toms

Hey @dc42, thanks for the heads up! So out0_neg isn't ground?

So the new, better, approach is...

12v power supplied to the 1LC Tool Board
Power and ground wires of the servo running to out1.VOUT and out1.GND pins (with the VOUT Jumper installed for 2amps @ 12v)
Signal wire running to io0.out

The config.g file

G4 S2                       ; wait for expansion boards to start
M950 S0 C"121.io0.out" Q250 ; io0.out 5v PWM capable, Q = 250Hz PWM Frequency

Interacting with the servo

M280 P0 S600  ; Moves the servo to lowest position
M280 P0 S2500 ; Moves the servo to highest position

dc42

@toms out0_neg isn't ground until out0 is turned on.