List of materials

3d printed parts

STL files for 3d printing are available here. The required tolerances are not very tight; any reasonable print settings should be fine.

picture of 3d printed parts

  1. head
  2. forehead
  3. rotors (you'll need two copies)
  4. servo mount
  5. battery box

Other parts

Here is a picture of most of the other parts you'll need (I forgot to include the batteries). I've tried to include Amazon and AliExpress purchase links where possible, but they tend to go stale. See the Notes section for more details on the parts, and some advice on substitutions.

picture of misc parts

  1. two stepper motors (28BYJ-48) (amazon, aliexpress)
  2. two stepper motor drivers (ULN2003); often sold in combination with the motors
  3. the wires that came with my stepper motors and drivers. You can also just supply your own wires.
  4. servo motor (sg90) (amazon, aliexpress)
  5. ESP32-C3FH4 dev board by WeAct Studio (aliexpress)
  6. DC step down converter, 5v output (amazon, aliexpress)
  7. Power switch (amazon, aliexpress)
  8. Terry clips, big enough to firmly hold your markers (amazon, aliexpress)
  9. Suction cups, (amazon)
  10. Thread (or fishing line)
  11. A bunch of M3 screws, and two M2 screws.
  12. Assorted wires, with "Dupont" style connectors and ring terminals (amazon, amazon, aliexpress, aliexpress)
  13. Two 9v rechargeable batteries, and two 9v battery connectors (not pictured)

Tools and equipment

  • soldering iron
  • 3d printer
  • screwdriver
  • hot glue gun
  • tool for cutting and stripping wire
  • crimping tool
  • USB-C data cable
  • computer

Notes

Motors and servos

28BYJ-48 stepper motors are made by many manufacturers, and often packaged with ULN2003 drivers. As of me writing this, a pack of 5 motors and 5 drivers is available for $15 on Amazon or $10 on AliExpress.

The pen is lifted with an SG90 servo, which is also made by many manufacturers. A 5-pack costs about $10 on Amazon, or $5 on AliExpress.

The batteries

I'm using two rechargeable 9v Li-ion batteries. At about $20 for a 4-pack on Amazon, this is definitely the most expensive part. You'll also need two 9v battery connectors with wire leads. A 10-pack is about $5 on Amazon.

Power supply

We'll power the device with 9v batteries, but that 9v needs to be converted down to 5v. Adjustable DC step-down converters are available in packs of 5 for about $10 on Amazon or $5 on AliExpress. Any cheap converter should be fine; we won't draw much current.

The brains

The device is controlled by an ESP32-C3 chip. Development boards with ESP32-C3 chips are available on AliExpress for as little as $2. There doesn't seem to be much difference between the different boards except for the locations of the various pins; probably any of them will work. But if you want to use the exact same board as me, I'm using WeAct Studio's ESP32-C3FH4 Core Board. This seems to be available only on AliExpress.

Pen holder

I'm using two terry clips to hold the marker in place. You can also use a binder clip, a rubber band, or anything else that holds the pen firmly in place.

Wiring

I cut my own wires to approximately the correct length; I connected the wires to the various devices using "Dupont"-style connectors, and I connected the power wires to one another using a screw and ring terminals. You can of course use pre-cut and pre-crimped wires if you prefer.

String

You'll need a few meters of string for hanging the device. Ordinary sewing thread works well (it isn't very heavy), as does fishing line.