A wall-hung cable plotter: two steppers pay out Dyneema line to a gondola that carries a technical pen across a vertical sheet.

The gondola is the design. Its structural core is a half-inch raw brass plumbing cross — 145 g of mass exactly where the pendulum wants it — with lubrication-free igus polymer bearings, a press-fit iglidur bushing in the pen bore, PTFE glide tape on the rear contact face, and a ring magnet glued to the back. A micro servo lifts the pen. Nothing about it is precious; almost all of it is plumbing stock, hardware-store parts, and two self-printed PETG spools.

Motion is 24 V through TMC2209 SilentStepSticks on a CNC Shield, stepped down to 5 V for the ESP32 by a buck converter that has to be trimmed before the board is ever connected.

The repository is not the firmware — it is the build guide. Every part carries a quantity, a price, a named vendor and a note, alongside the tools each step needs and the order to do them in. It is the production route for the coaster work.