SO-100 / SO-101 Arm

A sub-$300, open-source, 3D-printed robot arm built to pair with Hugging Face's LeRobot.

SO-100 is an open-source desktop robot arm co-designed by TheRobotStudio and Hugging Face, with 3D-printed structural parts; each arm uses 6 Feetech STS3215 serial-bus servos, 5 for joints and 1 for the gripper, and a leader-follower pair forms a teleoperation rig: a person moves the leader arm by hand, and the follower arm copies it and logs the data. SO-101, a 2025 revision, improved cable routing, no longer requires disassembling servo gears to build, and swapped in a different-gear-ratio servo for the leader arm. The official bill of materials lists a full leader-follower pair's parts at about $230. It plugs directly into the LeRobot library for data collection and training policies such as ACT and SmolVLA, making it one of the cheapest ways for a newcomer to get hands-on with imitation learning.

ExampleUsing an SO-101 leader-follower pair to collect 50 demonstrations of “put the block in the box,” then training an ACT policy with LeRobot so the follower arm can do it autonomously.

Also called

SO-100, SO-101, SO-ARM100, SO-ARM101

Related

LeRobot · Leader-Follower Teleoperation · Feetech STS3215 Servo · Action Chunking with Transformers · SmolVLA · Desktop Robot Arm

Sources

GitHub: TheRobotStudio/SO-ARM100
CNX Software: SO-ARM101 open-source dual robotic arm kit

As of

2025-05