Openbuilds Acro

Model Acro 1510

Openbuilds G-code generator


The blackbox motion controller runs on GRBL (see list of commands)

Prepare your drawing and export as SVG.

Go to This website generates the Gcode.

Load the SVG file.

In the documents section, select the layer.
In the Toolpaths section, click the green 'Add' button, then click on the popup 'Create a New operation'

Choose type of cut: other: Pen Plotter (no offset).
Set the servo limits:

  • For the Flexure mount:
    • Pen up: 232 (a higher number is further up)
    • Pen down: 143 (a lower number is further down)
    • Click apply

The M3Sxxx code in GRBL means Spindle ON (clockwise), with a speed of Sxxx. In Openbuilds this is repurposed to control the servo.

In the Toolpaths section: click 'Generate Gcode'.
Then click the 'save' icon.

  • Connect the USB cable of the pen plotter to the computer
  • Open the application 'Openbuilds Control'
  • Select the USB serial port and click Connect
  • Open the Gcode that was previously saved

This only needs to be done when you open the CONTROL software for the first time, or when the flexure Z-stage is changed.

  • In openbuilds CONTROL click 'Wizards & Tools'. Select 'Calibrate Servo Pen up/Down'
  • Drag the slider carefully:
    • Pen Up value: 20 (a lower value is a higher pen position)
    • Pen Down value: 89 (a higher value is a pen position)
  • Click Save & Apply

Note for advanced users

The servo horn is mounted on the servo shaft in such a way that it the zero position is a bit further than the desired pen up value: this allows for a bit of adjustment of the pen up value, while it avoids breaking the flexure. Clicking on the Calibrate Servo Pen Up/Down button 'homes' the servo before any adjustments can be made: it travels quickly to zero, and then back to its previous position. If the horn is mounted such that position zero won't over-stretch the flexure, this is safe to use.

For ballpoints

For pens that can handle a bit more pressure

  • In Openbuilds Control click 'Unlock Alarm'
  • Click Pen Up
  • If you didn't yet calibrate the pen up/down positions, click here
  • Insert the pen and screw it tight (don't over-tighten) so the point floats a few millimeters over the paper surface
    • You can put a thin piece of wood or cardboard underneath when tightening.

For felt tips and brushes

For pens that require delicate pressure

  • In Openbuilds Control click 'Unlock Alarm'
  • Click Pen Down
  • If you didn't yet calibrate the pen up/down positions, click here
  • Insert the pen and screw it tight (don't over-tighten) so the point touches the paper with the right pressure.
    • Instead of pushing down on the pen, you can also lift the flexure mount up a little bit before tightening

Tip: it might be a good idea to do this roughly in the middle of where the drawing will be.

todo: icons

  • Plug in the power from the Pen plotter
  • Turn on the driver (blackbox)
  • In Openbuilds Control:
    • Click 'Pen up' (if you forget this, the plotter will draw a line from the home position to the start of the drawing)
    • Click 'Home All'
    • Define the start position
      • Move the pen head to the right start location.
        Remember that the work origin is the left bottom of the SVG file.
        If you don't set this, the plotter will use the previously set zero point.
      • Click 'setzero'
    • Click 'Check Size' (this traces around the perimeter of the drawing to check the location and size of the work in the plotter)
    • Click 'Run Job'
  • Click pen up (if pen is not already up)
  • Use the arrows to move the pen away from the paper (in the rough direction of home). If you don't do this, the pen might drag on the paper while homing.
  • Click 'Home All'
  • Remove the pen
  • In Openbuilds Control, click 'Pen Down'. Don't forget this, as it releases tension on the flexure mount.
  • Disconnect the USB connection
  • Turn of the driver & unplug the plotter
  • Download an install Openbuilds CONTROL
  • Open it
  • Select USB serial connection and click 'connect'
    • The Grbl machine settings are transferred to your computer and you're good to go.
    • A popup will open. Configure the following settings:
      • Select your controller: Openbuilds Blackbox 4x
      • Select your machine: Openbuilds Acro with servo pen attachment.
        • select the 1510 model
      • Select your tool initialization
        • Leave this blank
      • Customise defaults
        • Do not change anything here

You're ready to start

  • Check belt tension after a crash. Re-tension by undoing one of the set screws, pulling on the GT2 belt by hand and retightening the set screw.
  • openbuilds_acro/openbuilds_acro.txt
  • Last modified: 2023/03/22 06:23
  • by formlab