SO-101
Technical Specifications
Full hardware and software specifications for the SO-101 open-source robot arm.
Mechanical
Mechanical
| Parameter | Value |
|---|---|
| Degrees of Freedom | 6 DOF 5 arm joints + 1 gripper |
| Actuators | Feetech STS3215 Serial bus servo, 15 kg·cm stall torque |
| Reach | ~500 mm |
| Payload | ~500 g Varies with arm pose and servo temperature |
| Weight (arm only) | ~800 g Depends on print material; PLA typical |
| Build Material | 3D-printed PLA + off-the-shelf hardware |
| Joint Type | Revolute (all joints) |
| URDF Available | Yes — community-maintained, included in LeRobot repo |
Electrical
Electrical
| Parameter | Value |
|---|---|
| Input Voltage | 12V DC 3A minimum power supply recommended |
| Servo Bus | Feetech STS serial bus (daisy-chained) |
| PC Interface | USB-to-serial adapter CH340 or CP2102 chip |
| Connector | JST-style servo connectors (per STS3215 standard) |
| Polarity Protection | None built-in — verify polarity before first connection |
Software
Communication & Software
| Parameter | Value |
|---|---|
| Communication | USB serial /dev/ttyACM* on Linux, /dev/tty.usbserial-* on macOS |
| Default Baud Rate | 115200 baud |
| LeRobot Device Type | so101
Use --robot.type=so101 in all LeRobot CLI commands
|
| SDK | HuggingFace LeRobot (pip install lerobot) |
| Python Version | 3.10+ |
| OS Support | Linux (Ubuntu 22.04+), macOS |
| Data Format | LeRobot dataset format (Parquet + video, HuggingFace Hub compatible) |
| Simulation | URDF available for MuJoCo and PyBullet integration |
Build & Cost
Build & Cost
| Parameter | Value |
|---|---|
| DIY Build Cost | ~$100–200 USD Varies by servo sourcing, print filament, and region |
| BOM Source | HuggingFace LeRobot GitHub repository |
| Printable Parts | STL files available in the SO-101 GitHub repo |
| Open Source License | Apache 2.0 (via LeRobot) |
| Predecessor | SO-100 (SO-101 is the updated version with improved servo mounts) |
Where to get parts: The full bill of materials is maintained in the HuggingFace LeRobot repository. Search for "SO-101" to find the current BOM and STL files. Servos can be sourced from Feetech directly or via common electronics suppliers.
BOM
Bill of Materials
Off-the-shelf components for a complete follower + leader teleoperation set. All structural parts are 3D-printed from STL files in the SO-ARM100 GitHub repo.
| Component | Qty (2-arm set) | Unit Cost (US) | Source |
|---|---|---|---|
| STS3215 7.4V 1/345 gear (C001) — follower joints & leader shoulder | 7 | ~$13.89 ea | Alibaba |
| STS3215 7.4V 1/191 gear (C044) — leader base & elbow | 2 | ~$13.89 ea | Alibaba |
| STS3215 7.4V 1/147 gear (C046) — leader wrist & gripper | 3 | ~$13.89 ea | Alibaba |
| Waveshare Motor Control Board | 2 | ~$10.60 ea | Amazon / Akizuki |
| USB-C Cable (2-pack) | 1 | ~$7.00 | Amazon |
| 5V DC Power Supply | 2 | ~$10.00 ea | Amazon |
| Table Clamps (4-pack) | 1 | ~$9.00 | Amazon |
| Screwdriver Set (Phillips #0 & #1) | 1 | ~$6.00 | Amazon |
| 3D-printed structural parts (PLA+ filament) | — | Filament cost only | Print yourself (STL in repo) |
Total estimated cost: ~$230 USD for a complete follower + leader set (US pricing). A single follower arm alone is approximately $122 USD. EU pricing is comparable (~€226 for the full set). Pre-assembled kits are available from PartaBot, Seeed Studio, and WowRobo.
Actuation
Leader Arm Gear Ratios
The follower arm uses a uniform 1/345 gear ratio on all 6 joints (STS3215 C001). The leader arm uses three different gear ratios to balance back-drivability with the ability to support its own weight:
| Joint | Motor | Gear Ratio | Part Code |
|---|---|---|---|
| Base / Shoulder Pan | STS3215 7.4V | 1 / 191 | C044 |
| Shoulder Lift | STS3215 7.4V | 1 / 345 | C001 |
| Elbow Flex | STS3215 7.4V | 1 / 191 | C044 |
| Wrist Flex | STS3215 7.4V | 1 / 147 | C046 |
| Wrist Roll | STS3215 7.4V | 1 / 147 | C046 |
| Gripper | STS3215 7.4V | 1 / 147 | C046 |
Lower ratio = more back-drivable. Joints the operator moves most frequently (wrist, gripper) use 1/147 for lighter resistance. The shoulder uses 1/345 for greater torque to hold the arm's own weight. The follower arm uses 1/345 everywhere for maximum stall torque.
Compare with other hardware
See how the SO-101 stacks up against other arms on the platform, including the OpenArm 101 and DK1 Bimanual Kit.
Compare All Hardware →