SO-101 vs SO-100 for LeRobot: what changed, what to buy

Published 2026-11-11 · Sources read 2026-11-11 · Not tested by us

Verdict first. If you're starting a LeRobot build today, the sources point to the SO-101: the repository calls it the next-generation version, marks the SO-100 docs as deprecated, and the LeRobot docs call the SO-101 their flagship arm. We haven't built either, so this is a reading of the public documentation, not a hands-on review.

The short comparison

Item	SO-100	SO-101	Source
Relationship	Original design by RobotStudio with Hugging Face	"Next-generation version of the SO-100"	[1]
Documentation status	"Deprecated" (SO-100 docs)	Current docs	[1]
Assembly	Not stated in the sources we read	"Improved wiring, easier to assemble (no gear removal)"	[1]
Leader-arm motors	Not stated	"Updated motors for the leader arm"	[1]
Follower servos	Not stated	6× STS3215 with 1/345 gearing	[2]
LeRobot tutorial	Not covered by the page we read	Step-by-step assembly, motor setup and calibration	[2]
Hands-on result	Not tested by us	Not tested by us	—

Servos and gearing

Per the LeRobot SO-101 page [2], the follower arm uses six STS3215 motors with 1/345 gearing. The leader arm uses three differently geared motors "to make sure it can both sustain its own weight and it can be moved without requiring much force":

Leader axis	Motor #	Gear ratio
Base / shoulder pan	1	1/191
Shoulder lift	2	1/345
Elbow flex	3	1/191
Wrist flex	4	1/147
Wrist roll	5	1/147
Gripper	6	1/147

Source [2], read 2026-11-11.

Power notes

The repository README [1] says the follower's STS3215 comes in two sizes: a 7.4 V version with a stall torque of 16.5 kg·cm at 6 V ("and likely slightly less for a 5V power supply"), and a 12 V version with a stall torque of 30 kg·cm. The authors write that they found the 7.4 V sufficient. Choosing 12 V motors also means a 12 V, 5 A+ supply instead of a 5 V one, and the leader arm is always 7.4 V for the SO-101. Read 2026-11-11.

Bill-of-materials snapshot

The README's parts table [1] lists the STS3215 servo at a unit cost of US$13.89 (the same row lists €12.2 for EU), in a two-arm parts list of 12 servos: 7× 1/345 (C001), 2× 1/191 (C044) and 3× 1/147 (C046). By our own arithmetic, 12 × US$13.89 = US$166.68 for servos alone. This is not a price for a complete arm: the table also lists other parts, 3D printing and a power supply, and the README itself notes that "prices and items may vary depending on geographic location." We have not checked current vendor prices.

The README also lists vendor kits (including 3D-printed kits) from several sellers; see the repository's Kits section [1]. We have no relationship with any of them and haven't bought from them.

Which one, if you only want to get running

Starting fresh: follow the SO-101 path. It is the one with a current LeRobot tutorial [2].
Already own an SO-100: the SO-100 docs are marked deprecated [1]. Check the current LeRobot docs for what is still supported before you plan a project around it.
Want to see what LeRobot does first: the LeRobot docs [3] describe a "Teleoperate → Record → Train → Deploy" flow and a no-install dataset visualizer.

What we haven't checked

Real-world accuracy, repeatability or payload (not stated in sources we read; not tested by us).
Current vendor prices and availability.
Printing quality or assembly time.

Sources

[1] SO-ARM100 repository README (TheRobotStudio / Hugging Face) — https://github.com/TheRobotStudio/SO-ARM100. Read 2026-11-11.
[2] LeRobot docs: SO-101 assembly and setup — https://huggingface.co/docs/lerobot/so101. Read 2026-11-11.
[3] LeRobot documentation home — https://huggingface.co/docs/lerobot/index. Read 2026-11-11.