SO-ARM100 vs SO-ARM101 vs SO-101: What Changed and Which Parts You Need
Share
The SO-101 is the 2025 revision of the SO-100, the low-cost 6-axis arm designed by TheRobotStudio for Hugging Face LeRobot. Vendors sell it as the "SO-ARM101" (Hiwonder, Seeed) but the geometry, servo protocol and LeRobot configs are the same open-source design. This guide lists the concrete differences and the parts you need to build or repair one.
What changed from SO-100 to SO-101
| Item | SO-ARM100 | SO-ARM101 |
|---|---|---|
| Leader arm servos | 6 × 7.4 V STS3215, all 1:345 | 6 × 7.4 V STS3215 in three ratios (1:345, 1:191, 1:147) so the leader is lighter to move and back-drives smoothly |
| Follower arm servos | 6 × 7.4 V or 12 V STS3215 | 6 × 12 V STS3215-C018 (30 kg·cm) recommended |
| Wrist | Straight wrist link | Redesigned wrist with more range and a built-in camera mount on the gripper |
| Wiring | Cables exposed along the links | Cable channels inside the links; easier routing, fewer snags |
| Base | Screw-down base | Base plate with slots for two G-clamps |
| LeRobot config |
so100_follower / so100_leader
|
so101_follower / so101_leader
|
What carries over
- All STS3215 servos, metal horns and 3-pin cables
- The USB servo interface: BusLinker V3.0 or the Waveshare Bus Servo Adapter (A)
- Power supplies, G-clamps and cameras
Parts list for one SO-101 leader + follower pair
| Part | Qty | Where to get it |
|---|---|---|
| STS3215 12 V (C018) for the follower | 6 | STS3215 singles and the 12-servo set |
| STS3215 7.4 V, three ratios, for the leader | 6 | Included in the 12-servo set |
| Metal main + rear horn sets | 12 | STS3215 metal horns, 6-set |
| USB servo adapter board | 2 | Waveshare adapter or BusLinker V3.0 |
| 3-pin servo cables (15 / 20 / 40 cm) | 24 | cable sets |
| 12 V 5 A adapter (follower) and 7.4 V 3 A adapter (leader) | 1 + 1 | 7.4 V servo adapter |
| 2-inch G-clamps | 4 | G-clamp 4-pack |
| 3D-printed parts | ~1 kg PLA | Free STL files with the SO-101 Builder's Pack |
| Wrist and overhead cameras (optional) | 1 + 1 | 1080p camera module and desk arm |
If you would rather not print anything, the assembled SO-ARM101 kits include everything above pre-built and calibrated.
FAQ
Is the SO-ARM101 the same as the SO-101?
Yes. SO-101 is the open-source design name from TheRobotStudio and Hugging Face; SO-ARM101 is the same design as sold in kit form by Hiwonder, Seeed and others. Parts, servos and LeRobot configs are interchangeable.
Can I upgrade an SO-ARM100 to a 101?
Partly. The servos, adapter boards and cables carry over. You need to print the new 101 leader parts (the leader's gear-ratio change and the new wrist) and, if you want the wrist camera, the 101 gripper with camera mount.
How many servos does a pair need?
Twelve: six 12 V STS3215 (C018) in the follower and six 7.4 V STS3215 in the leader, the leader mixing 1:345, 1:191 and 1:147 gear ratios so it is light to move by hand.