OpenBuilds BlackBox provides support for using an RC servo to raise/lower a pen, in Pen Plotter type applications, or other imaginative uses

Make sure to set $33=50 in grblHAL settings (CONTROL > Grbl Settings Tab > Scroll down to $33 Spindle PWM Frequency > Set the value to '50' and Save

TIP: Set $33=50 (PWM frequency), $34=5, $35=5 and $36=10 to generate a “standard” PWM signal: 20ms repetition rate, 1 - 2ms pulse length range. You may decrease $34 and $35 to output a shorter pulse than 1ms at min, and increase $36 to get a longer pulse than 2ms at max.

For most standard RC Servos that have moves 180 degrees when $34 and $35 are set to 2 and $36 to 15 - resulting in a 0.4 - 3ms pulse witdh range.

OpenBuildsCONTROL includes a tool to calibrate the Pen Up / Pen Down positions of your Servo. Please perform this step prior to trying out the Pen Up / Down values, and also note down the S-Values as advised by the Calibration Tool to use in your CAM setups later on.

Go to Wizards and Tools > Calibration > Calibrate Servo Pen Up / Down:

When $33 is set to 50hz, CONTROL will enable the Pen Up / Pen Down Buttons you can use to test you servo, check Pen Down positions to ensure your pen is touching the writing surface, etc