Open-source mini 6-DOF arm uses 3D-printed planetary gearboxes and closed-loop PID control

blaizedsouza · x · 2026-09-19

James Gullberg has open-sourced a mini 6-DOF robotic arm driven by low-cost stepper motors, featuring custom 3D-printed split-ring planetary gearboxes and an inverted belt differential wrist with custom bearings.

The firmware is written in C for the STM32 MCU on a BTT Octopus board, achieving full closed-loop PID control via daisy-chained AS5048A encoders over SPI. The controller communicates with a Raspberry Pi 5 over CAN bus, exchanging joint targets and joint states. The GitHub repo is public and serves as a solid reference for budget robot arm builders.

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