SO-101 Robot Arms
SO-101 Robot Arms is an Apache-2.0 physical design from TheRobotStudio with partial BOM data.
Source repository: https://github.com/TheRobotStudio/SO-ARM100
SO-101 at a glance
The SO-101 is The RobotStudio's second-generation 6-DOF desktop arm, built with Hugging Face for the open-source LeRobot stack. Against the deprecated SO-100 it improved its wiring, updated the leader-arm motors and assembles without removing servo gears. It is a leader/follower pair: the follower carries the gripper and executes motion, while the leader is the hand-guided arm you move by hand to teleoperate the follower or collect training data.
Source: TheRobotStudio/SO-ARM100 README (Apache-2.0).
Which arm are you building?
- Leader + follower teleoperation set — 12 servos in total.
- Single follower arm — 6 servos.
Motors by arm and gear
Both arms use Feetech STS3215 bus servos, but the gearing differs: the leader only has to sense hand motion, not drive a load.
- Follower arm — 6 × STS3215 7.4 V, 1/345 gear (C001).
- Leader arm — 1 × 1/345 (C001), 2 × 1/191 (C044), 3 × 1/147 (C046); 6 total.
- Leader + follower set — 7 × C001, 2 × C044, 3 × C046; 12 total.
Torque: the 7.4 V servo is rated 16.5 kg·cm stall at 6 V; a 12 V STS3215 reaches 30 kg·cm. The 7.4 V part is sufficient for both arms and the leader is always 7.4 V. Fitting 12 V servos to the follower also requires a 12 V 5 A+ power supply.
Typical cost (upstream list prices)
From the repository's own sourcing tables: one follower arm ≈ US21.94; the full leader + follower set ≈ US$229.88, so the leader arm adds ≈ US08. The two-arm set is ≈ €226.3 (EU) or ¥1343.16 (CN). These are the upstream README's figures, not supplier quotes; observed per-part catalogue prices appear separately above.
3D printing the frame
- Material PLA+, 0.4 mm nozzle at 0.2 mm layer height (or 0.6 mm nozzle at 0.4 mm).
- 15% infill; supports everywhere except slopes over 45° and screw holes on horizontal axes.
- Each arm prints as one pre-oriented STL: the Ender profile (220×220 mm bed) or the Prusa/UP profile (205×250 mm).
- Print a gauge (servo or Lego size) first to check dimensional accuracy before committing the full arm.
Assembly
The SO-101 is built without removing servo gears, which is the main reason to choose it over the SO-100. The step-by-step build and LeRobot setup live in the LeRobot SO-101 guide. Pre-built arms and part kits are offered by Seeed Studio, WowRobo, RobotEd, Robonine, PartaBot, ForgeMotion Labs and others linked from the repository.
Project facts
- Category: other
- Kind: physical design
- License: Apache-2.0
- GitHub stars: 7,085
- BOM lines indexed: 14
- Last updated: 2026-08-26
Bill of materials (14 lines)
- STS3215 Servo 7.4V, 1/345 gear (C001) 2 — 7 each (purchased, unresolved)
- STS3215 Servo 7.4V, 1/191 gear (C044) 2 — 2 each (purchased, unresolved)
- STS3215 Servo 7.4V, 1/147 gear (C046) 2 — 3 each (purchased, unresolved)
- Motor Control Board — 2 each (purchased, unresolved)
- USB-C Cable 2 pcs — 1 each (purchased, unresolved)
- Power Supply — 2 each (purchased, unresolved)
- Table Clamp 4pcs — 1 each (purchased, unresolved)
- Screwdriver Set 1 — 1 each (purchased, unresolved)
- STS3215 Servo 7.4V, 1/345 gear (C001) — 6 each (purchased, unresolved)
- Motor Control Board — 1 each (purchased, unresolved)
- USB-C Cable 2 pcs — 1 each (purchased, unresolved)
- Power Supply — 1 each (purchased, unresolved)
- Table Clamp 2pcs — 1 each (purchased, unresolved)
- Screwdriver Set 1 — 1 each (purchased, unresolved)
Repository files indexed (70)
45 CAD models, 3 URDF robot descriptions, 16 documents, 6 images. Paths are exactly as they appear in the project's repository; RoboPartPicker lists only files it has actually indexed.
CAD models (45)
- Mini/Mini_SO_100_01g.STL
- Optional/4040_Base_Mount/step/4040_base_mount.step
- Optional/4040_Base_Mount/stl/4040_base_mount.stl
- Optional/Compliant_Gripper/stl/Compliant_Moving_Jaw_SO101.stl
- Optional/Compliant_Gripper/stl/Compliant_Wrist_Roll_Follower_SO101.stl
- Optional/Mount_Helper/stl/mount_helper v2.stl
- 39 more CAD models are indexed in the catalogue.
URDF robot descriptions (3)
- Simulation/SO100/so100.urdf
- Simulation/SO101/so101_new_calib.urdf
- Simulation/SO101/so101_old_calib.urdf
documents (16)
- 3DPRINT.md
- CHANGELOG.md
- CITATION.cff
- LICENSE
- Mini/readme
- Optional/4040_Base_Mount/README.md
- 10 more documents are indexed in the catalogue.
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