Servo Motor and Pen Up/Down Not Working on OpenBuilds BlackBox

Hi everyone,

I’m using an OpenBuilds BlackBox to run a pen plotter and having issues controlling the pen lift with an SG90 servo motor.

Setup:

  • I’m using the latest version of OpenBuilds CONTROL.
  • The pen plotter uses an SG90 servo motor for pen up/down.
  • I’ve configured GRBL with laser mode enabled ($32=1) and set up PWM for the servo, but it’s not responding to G-code commands like M280 P0 S90 (pen down) or M280 P0 S0 (pen up).

Issues:

  1. Servo Control: The servo doesn’t respond, despite correct wiring and settings.
  2. G-code for Pen Movement: Using Z-axis commands (G0 Z5 for pen up, G0 Z0 for pen down) doesn’t work either.
  3. Missing 2 Axes + Servo Option: The 2 Axes + Servo option is not available in the GRBL Flashing Tool under Wizards and Tools, even though I’m using the latest version.

What I’ve Tried:

  • Manually sending G-code via the console.
  • Ensuring the power supply provides enough power for the servo.
  • Verifying GRBL settings for PWM control ($9=1, $33=50, $30=255, $32=1).

Questions:

  • Has anyone successfully controlled a servo motor for pen lifting on the BlackBox?
  • Any additional GRBL settings I need to adjust?
  • Why don’t I have the 2 Axes + Servo option, and how can I enable it?

Any help or suggestions would be greatly appreciated!

Hi @Rich_Saenz ,

Afik GRBL can only use the servo as a tool, not an axis. Which is why you won’t find it as a movement action, it cannot be used as the Z axis.

What happens when you switch the tool on and set it to the max pwm value, eg: send M3 S 1000?

You need to think of the servo as a tool, tool on = servo down, and vice versa.

1 Like

Okidoki; you may want to look at this:

…an older repo from Bart Dring, the creator of FluidNC and maker of pen-plotters.

If he felt the need to fork GRBL to make it work properly with pen plotters it probably menas there is no easy standard configuration for them…

1 Like