Distal pen arm for EggBot

by tml, published

Distal pen arm for EggBot by tml Feb 24, 2015
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This is a customisable version of the pen holder arms used by EggBots (http://shop.evilmadscientist.com/productsmenu/51-accessories/205-distalarm).

It was designed to be a solid, one piece object without any nuts and bolts for holding it together. It actually turned out to be 2 pieces glued together, as it's easier and faster to print this way.

To allow fitting different kinds of pens (for example Sharpie Ultrafine and Sharpie Fine markers), the pen arm itself contains a hole for an pen adaptor module. This way, when you want to change pens, you only need to replace the adaptor with another one and you get a tight fit on any pen of yours.

I supplied STLs for adaptors for the ultrafine Sharie and for the fine-point Sharpie. If you want to use a custom pen, a configurable OpenSCAD file is available where you can change the diameters around.

The OpenSCAD file also allows the customization of various parameters, like the length of the arm, the thickness of the piece and the diameter of the bolt fixing the pen.

Extra parts needed:

  • 1x M3 nut
  • 1x M3 bolt

Compatible with Basic, Deluxe and Ostrich EggBots. You can use the same S90 TowerPro servo on this arm as on the one you got from EvilMadScientist.

Update 1 @ 2015-04-12

  • increased the thickness of the "thin part" of the pen arm from one layer thickness (0.2mm) to two layer thickness (0.4mm) to increase durability
  • modified the OpenSCAD script printing the pen adaptors so that you can specify the to diameter and bottom diameter of the adaptor module in order to model the shape of the pen better.
  • updated the ultra fine sharpie STL to have better dimensions


The supplied STL files have been generated from the OpenSCAD file. They are configured for a standard EggBot, for use with an M3 bolt and nut as pen fixers and contain adaptors for the ultrafine Sharpie and the fine Sharpie markers.

  1. Print all STL files
  2. Glue the "stepper arm" and the "pen arm" together
  3. Put an M3 nut into the shaft designed for it, found on the inside of the hole for the pen adaptor on the pen arm
  4. Insert the pen adapter (fine.stl and ultrafine.stl) into the hole designed for them on the pen arm

Pretty straightforward. If you want to customize it, take a look at the SCAD file, it even has comments. The most important settings in it:

  • l1: size of the stepper arm
  • l2: size of the pen arm
  • thickness: thickness of the arms
  • gap: gap to leave between objects that should fit into each other. For printers that are not 100% exact. Like mine.
  • screwDiameter: diameter of the bolt fixing the pen in its place.
  • nutDiameter: diameter of the nut for holding the bolt
  • nutThickness: size of the shaft to house the nut
  • diameter parameter for the penHolder() module: Diameter of the pen to print an adapter for.

At the end of the OpenSCAD file you will find module calls that you can comment out to obtain the specific parts you want.

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Nice idea. Thank you for sharing it.