No updates since 2024, and its makers moved on to the cheaper SO-101.
The Koch arm is a low-cost 3D-printed arm built around Robotis Dynamixel XL430 and XL330 servos, originally designed by Alexander Koch and used as a leader and follower pair for teleoperation and imitation learning. Version 1.1, published in a separate repository, cleaned up the CAD, added a wiring diagram and assembly video, and removed the need for soldering. It was one of the first arms supported by LeRobot and preceded the cheaper SO-101.
At a glance
| Parts cost | $480 (2024) project · Stated by the project for v1.1 in the US, $199 for the leader arm plus $278 for the follower source ↗ |
|---|---|
| Difficulty | 2/5 Easy · Bolt-together printed parts and Dynamixel servos, but servo power wiring has tripped up many builders. |
| Build time | Not stated |
| Tools needed | 3D printer (PLA+, ABS or PETG, about 30% infill; print time not stated), 1.5 mm cross screwdriver, no soldering in v1.1 (v1 needed soldering) |
| Motors | Follower uses 2x Dynamixel XL430-W250 + 4x XL330-M288; leader uses 6x XL330-M077 |
| Controller | Waveshare serial bus servo driver board per arm, USB to a PC (LeRobot or Dynamixel SDK) |
| Sensors | Servo position encoders |
| Published | ✓ Parts list✓ CAD/STL✓ Assembly guide✓ Wiring✓ Software✓ Video GitHub README with parts list tables, STL and SolidWorks files, wiring diagram PDF and YouTube assembly video |
| Activity | Last update 2024-09-17 · 733 GitHub stars · v1.1 repo 733 stars and 68 forks; original repo 3,422 stars and 301 forks (last commit 2024-09-21) |
| Kits | PartaBot sells Koch robots (per the SO-ARM100 README); original author ran a parts waitlist via tau-robotics.com (unconfirmed whether it shipped) |
Licenses
| Design files | Apache-2.0 (v1.1 repo-wide LICENSE covering STL, SolidWorks files and wiring PDF); MIT for the original v1 files source ↗ |
|---|---|
| Code | MIT (original repo, control scripts); Apache-2.0 (v1.1 repo) source ↗ |
| Documentation | Apache-2.0 (v1.1) / MIT (v1), repo-wide, no separate docs license source ↗ |
Builder notes
Practical points from the project's issue tracker, forum and docs, each linked to its source.
- Two repos exist. The original by Alexander Koch is the v1 design under MIT, while the improved v1.1 (fixed screw clashes, leader platform, no soldering, wiring PDF) lives in a separate repo under Apache-2.0. Neither has had commits since September 2024. source ↗
- On the original design, feeding 12V to the small XL330 servos destroys them. They must run from 5V, which is why v1 used a separately adjusted voltage reducer. source ↗
- The Waveshare board's servo headers do not accept Dynamixel cables directly, so builders used jumper wires between board and first servo. source ↗
- The original repo's URDF models an older 5-DOF arm, not the 6-DOF arm in the photos. source ↗
- In v1.1 the printed leader platform differs from what the assembly video shows, since the part was changed to a screwed fit after the video was made. source ↗
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