Overview • Prerequisites • Motor ID Programming • Assembly at Neutral Positions • Calibration • Teleoperation • Adding a Camera • Troubleshooting
The SO-101 is a 6-DOF desktop robot arm built around the Feetech STS3215 servo motor. This guide covers the complete workflow to go from unassembled hardware to a fully functional bilateral teleoperation system using two arms (a leader and a follower).
| Joint # | Motor Name | ID | Role |
|---|---|---|---|
| 1 | shoulder_pan | 1 | Base rotation (left/right) |
| 2 | shoulder_lift | 2 | Shoulder pitch (up/down) |
| 3 | elbow_flex | 3 | Elbow bend |
| 4 | wrist_flex | 4 | Wrist pitch |
| 5 | wrist_roll | 5 | Wrist rotation |
| 6 | gripper | 6 | Gripper open/close |
| Component | Leader Arm | Follower Arm |
|---|---|---|
| Controller Board | Feetech serial board | Feetech serial board |
| USB Port | /dev/ttyACM1 |
/dev/ttyACM0 |
| Power Supply | 5 V external PSU | 12 V external PSU |
| Motors | 6 × Feetech STS3215 | 6 × Feetech STS3215 |
Note: Your actual ports (
/dev/ttyACM0,/dev/ttyACM1) may differ. Runuv run lerobot-find-portto identify each arm's port after connecting the bus adapter.
The leader arm uses lighter, faster motors since it only needs to sense and transmit joint positions (no payload to carry).
| Joint # | Motor Name | Model | Gear Ratio | Stall Torque | Operating Voltage | Encoder |
|---|---|---|---|---|---|---|
| 1 | shoulder_pan | STS3215-C046 | 1 : 147 | ~14.4 kg·cm | 5 V | 12-bit |
| 2 | shoulder_lift | STS3215-C001 | 1 : 345 | ~19 kg·cm | 5 V | 12-bit |
| 3 | elbow_flex | STS3215-C046 | 1 : 147 | ~14.4 kg·cm | 5 V | 12-bit |
| 4 | wrist_flex | STS3215-C046 | 1 : 147 | ~14.4 kg·cm | 5 V | 12-bit |
| 5 | wrist_roll | STS3215-C046 | 1 : 147 | ~14.4 kg·cm | 5 V | 12-bit |
| 6 | gripper | STS3215-C046 | 1 : 147 | ~14.4 kg·cm | 5 V | 12-bit |
Note: J2 (
shoulder_lift) uses the higher-torque C001 variant (1:345 gear ratio) because the shoulder lift joint bears the most static load even on the leader arm.
The follower arm uses the C018 variant across all 6 joints. This variant shares the same high gear ratio (1:345) as the C001 but is rated for 5V operation, providing substantially more holding torque to carry objects and resist gravity during task execution.
| Joint # | Motor Name | Model | Gear Ratio | Stall Torque | Operating Voltage | Encoder |
|---|---|---|---|---|---|---|
| 1 | shoulder_pan | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
| 2 | shoulder_lift | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
| 3 | elbow_flex | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
| 4 | wrist_flex | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
| 5 | wrist_roll | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
| 6 | gripper | STS3215-C018 | 1 : 345 | ~30 kg·cm | 12 V | 12-bit |
Common specs across all variants: TTL serial bus (half-duplex), 1 Mbps baud rate, 4096 steps/360° resolution, metal gears (backlash ≤ 0.5°), dimensions 45.2 × 24.7 × 35 mm, weight ~55 g.
Caution
Do not mix C018 and C046 motors on the same arm without updating the calibration. The gear ratio difference (1:345 vs 1:147) means an identical encoder movement produces a different physical joint angle on each variant.
| Requirement | Minimum Version |
|---|---|
| Python | 3.12 or later |
| Git | Any recent version |
| OS | Ubuntu 22.04 / Linux (tested) |
| USB serial port | /dev/ttyACM* (bus adapter) |
LeRobot uses uv as its package manager. Install it if not already present:
curl -LsSf https://astral.sh/uv/install.sh | sh
source $HOME/.cargo/env # or restart your terminalVerify the installation:
uv --versionOn Linux, your user must be in the dialout group to access /dev/ttyACM* serial ports without sudo:
sudo usermod -aG dialout $USERImportant
Log out and log back in (or reboot) after running this command for the group change to take effect. Without this, all motor bus commands will fail with a Permission denied error.
Clone the repository and install the base dependencies with Feetech motor support:
git clone https://github.com/rigbetellabs/lerobot.git
cd lerobot
# Base install — motor control, calibration, teleoperation
uv sync --locked --extra feetechThe --display_data=true flag on the teleoperate command requires the rerun-sdk visualization library. Install it together with the Feetech extra to avoid dependency conflicts:
# Install both together — installing viz alone will remove feetech dependencies
uv sync --locked --extra feetech --extra vizWarning
Do not run uv sync --extra viz alone after already installing Feetech. The uv sync command resolves a fresh lockfile and will remove previously installed extras. Always specify all required extras together in a single command.
Camera capture via OpenCV is included in the base dependencies (opencv-python-headless is a core dependency). No additional install is needed for USB webcams.
If you plan to use an Intel RealSense depth camera, install the RealSense extra:
uv sync --locked --extra feetech --extra viz --extra intelrealsenseThe set_middle_positions.py script (included in this repository) is used to program motor IDs and center each joint before assembly. No additional install is required — it uses the same feetech extra installed above.
Connect the bus adapter for one arm at a time (the arm does not need to be assembled — only the controller board needs to be connected via USB), then run:
uv run lerobot-find-portNote the port printed (e.g. /dev/ttyACM0) for the connected bus adapter, then connect the second arm's bus adapter and repeat.
Every motor ships from the factory with ID = 1 and default baud rate. Before assembly, each motor must be programmed with its unique ID (1–6) so the controller can address them individually.
Caution
Connect only ONE motor at a time when programming IDs. If multiple motors share the same ID on the same bus simultaneously, the communication protocol will fail and you will corrupt addresses on multiple motors at once.
Connect only the target motor's cable, then run:
# Example: program the elbow_flex motor (ID 3) on the leader arm
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 3The script will:
- Scan across all standard baud rates to find the connected motor.
- Reprogram the baud rate to
1,000,000if it is not already set. - Write the target ID into the motor's EEPROM.
- Move the motor to its neutral middle position (
2047).
Repeat the above for all 6 motors on each arm:
# Leader arm (replace /dev/ttyACM1 with your actual port)
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 1 # shoulder_pan - motor 0
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 2 # shoulder_lift - motor 1
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 3 # elbow_flex - motor 2
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 4 # wrist_flex - motor 3
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 5 # wrist_roll - motor 4
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 6 # gripper - motor 5
# Follower arm (replace /dev/ttyACM0 with your actual port)
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 1 # shoulder_pan - motor 0
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 2 # shoulder_lift - motor 1
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 3 # elbow_flex - motor 2
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 4 # wrist_flex - motor 3
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 5 # wrist_roll - motor 4
uv run python set_middle_positions.py --port /dev/ttyACM0 --id 6 # gripper - motor 5If you physically replace one motor (e.g. the elbow flexor), run only the script for that specific ID with only the new motor connected:
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 3Before attaching the structural arm links (horns, brackets, connectors), every motor must be set to its encoder midpoint (~2047) first. This ensures all joints are physically at 0° when the calibration defines them as 0°, giving the arm the maximum symmetrical range of motion in both directions.
Important
Never attach a joint link to a motor that is not at its midpoint. If the horn is attached at the wrong angle, the arm's software range will be mechanically offset and the arm may damage itself during teleoperation or policy rollout.
- Run the helper for the target motor ID. The motor will spin to
2047and hold. - With the motor holding torque, slide the structural link or horn onto the spline shaft.
- Align the link so the arm is at its natural resting position (vertical / flat / straight) at this angle.
- Tighten the set screw or push-fit horn to lock the angle.
- Press Enter in the terminal.
# Run all 6 motors sequentially on the leader
uv run python set_middle_positions.py --port /dev/ttyACM1
# Or run a specific motor only
uv run python set_middle_positions.py --port /dev/ttyACM1 --id 4Warning
Overload Error during assembly: If the motor is mechanically blocked and cannot reach 2047, the firmware will trigger an Overload protection flag and stop responding.
To recover: power-cycle the arm (turn off/on the 5V supply) and retry after clearing the mechanical obstruction.
The following images show the correct neutral position for each joint of the follower arm at encoder midpoint (~2047) before locking the horn.
| Joint | Motor Name | Assembly Reference |
|---|---|---|
| J1 | shoulder_pan |  |
| J2 | shoulder_lift |  |
| J3 | elbow_flex |  |
| J4 | wrist_flex |  |
| J5 | wrist_roll |  |
| J6 | gripper |  |
For the leader arm, J1–J5 assembly is identical to the follower arm (refer to the table above). Only the gripper (J6) differs due to a different motor variant:
| Joint | Motor Name | Assembly Reference |
|---|---|---|
| J6 | gripper |  |
Calibration records the real encoder range_min and range_max for each joint as you manually move the arm through its full range of motion. The result is saved as a JSON file (my_leader.json / my_follower.json) and used at runtime to normalize motor positions to degrees.
Caution
Do not force the arm past its natural mechanical stop. Moving a joint beyond its physical limit during calibration risks stripping the gearbox and is irreversible.
uv run lerobot-calibrate \
--teleop.type=so101_leader \
--teleop.port=/dev/ttyACM1 \
--teleop.id=my_leaderFollow the on-screen prompts. The GUI will guide you through each joint:
- Move the joint to its minimum angle and hold.
- Press the button in the calibration GUI to record the minimum.
- Move the joint to its maximum angle and hold.
- Press the button to record the maximum.
- Repeat for each joint until all 6 are done.
uv run lerobot-calibrate \
--robot.type=so101_follower \
--robot.port=/dev/ttyACM0 \
--robot.id=my_followerNote
Recalibrate whenever a motor is replaced. Swapping a physical servo motor resets its internal homing offset register. Running calibration again generates a fresh my_follower.json that accurately reflects the new motor's neutral position.
The elbow joint can sometimes reach encoder value 0 (the absolute hardware minimum of the 12-bit encoder) when fully extended. If range_min records as 0, leave a small physical margin (stop just before the hard mechanical limit) to prevent the arm from grinding against its own stop during teleoperation.
With both arms calibrated and all motor IDs programmed, you can begin leader-follower teleoperation.
Important
External 5V power supply must be ON for both arms before running any teleoperation command. The Feetech STS3215 motors cannot operate on USB bus power alone. Ensure the external 5V PSU is connected to the controller board and switched on. Running without it will cause Input voltage error faults on every motor.
uv run lerobot-teleoperate \
--robot.type=so101_follower \
--robot.port=/dev/ttyACM0 \
--robot.id=my_follower \
--teleop.type=so101_leader \
--teleop.port=/dev/ttyACM1 \
--teleop.id=my_leaderAdd --display_data=true to open a Rerun visualization window showing live joint positions being sent from the leader to the follower in real time:
uv run lerobot-teleoperate \
--robot.type=so101_follower \
--robot.port=/dev/ttyACM0 \
--robot.id=my_follower \
--teleop.type=so101_leader \
--teleop.port=/dev/ttyACM1 \
--teleop.id=my_leader \
--display_data=trueIf rerun-sdk is not installed, install it first:
uv sync --extra feetech --extra vizRerun Visualization Window:
If you replaced a motor since the last calibration, the script will display:
Mismatch between calibration values in the motor and the calibration file...
Press ENTER to use provided calibration file, or type 'c' and press ENTER to run calibration:
Type c and press Enter to re-run calibration inline. This is equivalent to running lerobot-calibrate separately.
A USB camera mounted on the follower arm provides a first-person visual feed during teleoperation. The camera used on the follower arm is the Waveshare IMX335 5MP USB Camera — Model (B).
| Specification | Value |
|---|---|
| Model | Waveshare IMX335-5MP-USBC-B |
| Image Sensor | Sony IMX335 |
| Sensor Size | 1/2.8" |
| Max Resolution | 2592 × 1944 (5 MP) |
| Frame Rates | 2592×1944 @ 30 FPS · 1920×1080 @ 30 FPS · 1280×720 @ 30 FPS |
| Field of View | 175° (Diagonal) — Ultra-wide angle |
| Focus | Fixed Focus |
| Aperture | F2.0 |
| Interface | USB 2.0 (UVC, plug-and-play) |
| Supported Formats | MJPG, YUY2 |
| Extra Features | Wide Dynamic Range (WDR), Built-in microphone |
| Linux Device | /dev/video3 (verified) |
| Used Resolution | 640 × 480 @ 30 FPS (MJPG) |
Note: The Model (B) is plug-and-play on Linux — no driver installation required. The 175° ultra-wide FOV captures the full arm workspace from a close-mount position.
To confirm your camera's device index:
uv run lerobot-find-camerasOr verify with ffplay (uses MJPEG format for better USB bandwidth efficiency):
ffplay -f v4l2 -input_format mjpeg -video_size 640x480 /dev/video3uv run lerobot-teleoperate \
--robot.type=so101_follower \
--robot.port=/dev/ttyACM0 \
--robot.id=my_follower \
--teleop.type=so101_leader \
--teleop.port=/dev/ttyACM1 \
--teleop.id=my_leader \
--robot.cameras="{front: {type: opencv, index_or_path: 3, width: 640, height: 480, fps: 30, fourcc: MJPG}}" \
--display_data=trueTip
If you get a black frame or the camera fails to open, try using the full device path instead of the index:
--robot.cameras="{front: {type: opencv, index_or_path: /dev/video3, width: 640, height: 480, fps: 30, fourcc: MJPG}}"Caution
Fix the camera mount before starting. The camera position and angle must remain identical between sessions. Any change in camera viewpoint will affect the consistency of your visual observations.
Cause: The external power supply is off, disconnected, or providing insufficient current.
Fix:
- Verify the 5V external PSU is plugged into the controller board and the wall outlet, and the power switch is ON.
- Check that all daisy-chain cables between motors are fully seated.
- Power-cycle the arm (turn off, wait 2 seconds, turn on) to clear the fault flag.
- Re-run your command.
Cause: The motor drove into a mechanical hard stop or was blocked and overloaded its own current limit.
Fix:
- Manually relieve the mechanical obstruction (move the joint by hand away from the hard stop).
- Power-cycle the arm to clear the Overload protection flag.
- Re-run your command.
Cause: A motor on the bus lost power or its cable disconnected mid-operation, breaking all communication on the shared daisy-chain.
Fix:
- Check all daisy-chain JST cables for loose connections.
- Check the connector on the motor where the error was reported (last ID before the break in the chain).
- Power-cycle and re-run.
Cause: Either the cable is not connected, or the motor is already in Overload/fault state.
Fix:
- Ensure the cable is firmly inserted into the motor socket.
- Power-cycle the arm.
- Confirm you are using the correct
--portfor the connected arm.
Cause: A motor was replaced, repositioned, or the arm was reassembled since the last calibration run.
Fix: Re-run calibration:
uv run lerobot-calibrate \
--robot.type=so101_follower \
--robot.port=/dev/ttyACM0 \
--robot.id=my_followerCause: Leader types (so101_leader) must use --teleop.* flags. Follower types (so101_follower) must use --robot.* flags.
| Hardware | Correct Prefix |
|---|---|
| Leader arm | --teleop.type=so101_leader |
| Follower arm | --robot.type=so101_follower |
# Find ports
uv run lerobot-find-port
# Program a motor's ID (connect only that motor first!)
uv run python set_middle_positions.py --port /dev/ttyACM1 --id <1-6>
# Setup motor IDs via official tool (leader)
uv run lerobot-setup-motors --teleop.type=so101_leader --teleop.port=/dev/ttyACM1
# Calibrate leader
uv run lerobot-calibrate --teleop.type=so101_leader --teleop.port=/dev/ttyACM1 --teleop.id=my_leader
# Calibrate follower
uv run lerobot-calibrate --robot.type=so101_follower --robot.port=/dev/ttyACM0 --robot.id=my_follower
# Teleoperate (no camera)
uv run lerobot-teleoperate \
--robot.type=so101_follower --robot.port=/dev/ttyACM0 --robot.id=my_follower \
--teleop.type=so101_leader --teleop.port=/dev/ttyACM1 --teleop.id=my_leader
# Teleoperate with camera + live display
uv run lerobot-teleoperate \
--robot.type=so101_follower --robot.port=/dev/ttyACM0 --robot.id=my_follower \
--teleop.type=so101_leader --teleop.port=/dev/ttyACM1 --teleop.id=my_leader \
--robot.cameras="{front: {type: opencv, index_or_path: 3, width: 640, height: 480, fps: 30, fourcc: MJPG}}" \
--display_data=true
Designed, assembled, and maintained by the team at
RigBetel Labs LLP®
Charholi Bk., via. Loheagaon, Pune – 412105, MH, India 🇮🇳
🌐 RigBetelLabs.com |
📞 +91-8432152998 |
📨 info@rigbetellabs.com
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