The SO-101 is a small 3D-printed 6-axis arm built from Feetech STS3215 serial bus servos, designed by The Robot Studio with Hugging Face. It is normally built as a pair, a follower arm plus a lighter leader arm that a person moves by hand, so demonstrations can be recorded and used to train AI policies in the LeRobot library. It replaces the earlier SO-100.
At a glance
| Parts cost | $230 project · The project's US parts list totals $229.88 for a leader and follower pair, excluding 3D printing. A single follower arm is about $122 source ↗ |
|---|---|
| Difficulty | 2/5 Easy · Printed parts plus off-the-shelf servos and screws, no soldering, but print tolerances and calibration take care. |
| Build time | Not stated |
| Tools needed | 3D printer (PLA+, 0.2 mm layers, 15% infill; print time not stated), small Phillips screwdrivers #0 and #1, no soldering |
| Motors | 12x Feetech STS3215 serial bus servos (6 per arm; leader uses mixed 1/345, 1/191 and 1/147 gearing) |
| Controller | Waveshare-type serial bus servo driver board per arm, connected over USB to a PC running LeRobot |
| Sensors | Servo position encoders; optional wrist and overhead USB cameras |
| Published | ✓ Parts list✓ CAD/STL✓ Assembly guide✗ Wiring✓ Software✓ Video GitHub README (parts list, printing) + Hugging Face LeRobot docs page with per-joint assembly videos |
| Activity | Last update 2026-09-23 · 7,639 GitHub stars · Discord linked from README; 708 forks; LeRobot repo has about 27.9k stars |
| Kits | Kits and assembled arms from several vendors listed in the README, including Seeed Studio, WowRobo, PartaBot, RobotEd and ForgeMotion Labs |
Licenses
| Design files | Apache-2.0 (single repo-wide license covering STL, STEP and docs) source ↗ |
|---|---|
| Code | Apache-2.0 (LeRobot library) source ↗ |
| Documentation | Apache-2.0 (same repo-wide LICENSE, no separate docs or media license) source ↗ |
Builder notes
Practical points from the project's issue tracker, forum and docs, each linked to its source.
- The SO-100 docs are marked deprecated. The SO-101 changed the wiring, removed the need to strip servo gears for the leader arm and changed the leader motors, so SO-100 guides and parts lists do not map one to one. source ↗
- The leader arm needs three different STS3215 gear ratios in specific joints (1/191, 1/345, 1/147), so a bag of identical servos will not build a correct leader. source ↗
- Several builders found servos or parts too tight to fit after printing. The repo ships fit gauges, and the community fix is printing those first and using the slicer's XY size or hole compensation. source ↗
- Vibration in the base and shoulder joints during teleoperation was traced to servo settings rather than loose prints. Lowering the minimum startup force on those two motors fixed it for one builder. source ↗
- A 12V STS3215 variant with more torque is an option, but it needs a 12V supply of at least 5A instead of the stock 5V one, and the leader arm stays on 7.4V servos. source ↗
Other arms plans
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- EEZYbotARM MK2 · $100 (2018) · difficulty 2/5
- GELLO teleoperation arms · $280 (2023) · difficulty 2/5
- Thor arm · $390 · difficulty 4/5
- reBot-DevArm (Seeed Studio) · $1,500 · difficulty 4/5
- OpenArm · $6,500 · difficulty 5/5
- Koch v1.1 arm · $480 (2024) · difficulty 2/5
- ROBOTIS OpenMANIPULATOR-X · $1,600 · difficulty 2/5
- BCN3D Moveo · $430 · difficulty 4/5
- PAROL6 · $970 · difficulty 4/5
- Faze4 robotic arm · $1,000–$1,500 (2020) · difficulty 4/5