Build SO-101 (SO-ARM101)

Steps

21

Subassemblies

9

Hands-on time (sum)

1 h

Critical path

1 h

Your progress · this device

—

20 steps have no time estimate; times above are lower bounds.

1. Fabrication
   01

   Check printer accuracy with the fit gauges

   Level and clean the bed, then print Gauge_0 and Gauge_tight_1 from STL/Gauges (or the two Lego gauges if you have no servo yet) at the arm settings: PLA+, 0.4 mm nozzle at 0.2 mm layers, 15% infill.

   CHECKAn STS3215 (or a 4x2 Lego brick) slides into Gauge_0 with the snug fit shown in the upstream fit video. If it is loose or will not go in, adjust flow or XY compensation and reprint before printing the arm.

   Parts in

   • Fit gauges: Gauge_0 + Gauge_tight_1 (against an STS3215), or Lego_Size_Test_02_zero + _minuspoint1 (against a 4x2 Lego brick)printed.gauges

   Tools

   FDM printer, 220x220 mm bed or larger, PLA+ filament

   Torque

   —

   Time

   1 h

   After

   Start

   Source

   github.com

2. Software
   02

   Install LeRobot with the Feetech SDK

   `conda create -y -n lerobot python=3.12 && conda activate lerobot`, `conda install ffmpeg -c conda-forge`, then `git clone https://github.com/huggingface/lerobot.git && cd lerobot && pip install -e ".[feetech]"`. Add `".[core_scripts]"` for record/replay and `".[training]"` (or `".[smolvla]"`) for training.

   CHECK`lerobot-setup-motors --help` and `lerobot-calibrate --help` print their usage without import errors.

   Parts in

   —

   Tools

   Linux, macOS or Windows computer, conda (miniforge) or uv

   Torque

   —

   Time

   —

   After

   Start

   Source

   huggingface.co

3. Motor setup
   03

   Sort and label the 12 servos by gear ratio

   Follower: six C001 (1/345). Leader, per joint: 1 shoulder pan = 1/191 (C044), 2 shoulder lift = 1/345 (C001), 3 elbow flex = 1/191 (C044), 4 wrist flex = 1/147 (C046), 5 wrist roll = 1/147 (C046), 6 gripper = 1/147 (C046). The mixed ratios let the leader hold its own weight yet move with little force. Label each servo with arm and joint number now; they look identical once assembled.

   CHECK12 labelled servos: F1-F6 all C001; L1 and L3 C044, L2 C001, L4-L6 C046, matching the sticker on each case.

   Parts in

   • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
   • Feetech STS3215 servo, 7.4 V, 1/191 gear (C044): leader joints 1 (shoulder pan) and 3 (elbow flex)actuator.sts3215-c044
   • Feetech STS3215 servo, 7.4 V, 1/147 gear (C046): leader joints 4 (wrist flex), 5 (wrist roll), 6 (gripper)actuator.sts3215-c046

   Tools

   Marker or labels

   Torque

   —

   Time

   —

   After

   Start

   Source

   huggingface.co

4. Fabrication
   04

   Print the leader and follower part plates

   Print one follower plate and one leader plate, already oriented Z-up: Ender_Follower_SO101.stl / Ender_Leader_SO101.stl for 220x220 mm beds, Prusa_*_SO101.stl for 205x250 mm beds, or BambuLabA1mini_*_SO101.stl. Supports everywhere except slopes steeper than 45°, no supports inside horizontal screw holes. No printer: upload the 14 individual STLs to Craftcloud (PLA+, 20% infill; shared parts qty 2; skip `SO101 Assembly.stl`) or the two Ender plates to PCBWay.

   CHECKYou have 9 shared parts x2 (base, base motor holder, rotation pitch, shoulder motor holder, upper arm, under arm, wrist motor holder, wrist roll pitch, driver plate), plus Wrist_Roll/Handle/Trigger for the leader and Wrist_Roll_Follower/Moving_Jaw for the follower.

   Parts in

   • Base_SO101 (arm base, clamps to the table)printed.base
   • Base_motor_holder_SO101 (motor 1 holder)printed.base-motor-holder
   • Rotation_Pitch_SO101 (shoulder part)printed.rotation-pitch
   • Motor_holder_SO101_Base (shoulder motor holder)printed.motor-holder-base
   • Upper_arm_SO101printed.upper-arm
   • Under_arm_SO101 (forearm)printed.under-arm
   • Motor_holder_SO101_Wrist (motor 4 holder)printed.motor-holder-wrist
   • Wrist_Roll_Pitch_SO101 (wrist holder for motor 5)printed.wrist-roll-pitch
   • WaveShare_Mounting_Plate_SO101 (or Seeedstudio_Mounting_Plate_SO101 to match your board; print one type only)printed.driver-plate
   • Wrist_Roll_SO101 (leader holder, leader only)printed.leader-wrist-roll
   • Handle_SO101 (leader only)printed.leader-handle
   • Trigger_SO101 (leader only)printed.leader-trigger
   • Wrist_Roll_Follower_SO101 (static gripper jaw, follower only)printed.follower-wrist-roll
   • Moving_Jaw_SO101 (follower only)printed.follower-moving-jaw

   Tools

   FDM printer, Slicer (Bambu Studio, PrusaSlicer or Cura)

   Torque

   —

   Time

   —

   After

   01

   Source

   github.com

5. Motor setup
   05

   Power the boards and find each arm's USB port

   Safety · human-verified required

   On the Waveshare board set both jumpers to channel `B` (USB). Plug in the 5 V supply (mains adapter) and USB-C. Run `lerobot-find-port` and unplug the board when prompted; repeat for the second board. On Linux you may need `sudo chmod 666 /dev/ttyACM0 /dev/ttyACM1`.

   CHECK`lerobot-find-port` prints `The port of this MotorsBus is /dev/ttyACM1` (or `/dev/tty.usbmodem...` on macOS, `COMx` on Windows) for each board, and you have written down which port is leader and which is follower.

   This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

   Parts in

   • Motor control board: Waveshare serial bus servo driver (USB-C), one per armelectronics.bus-servo-adapter
   • USB-C cable, 2-pack (board to computer)cable.usb-c
   • DC power supply, 5 V, 5.5x2.1 mm barrel (one per arm, for the 7.4 V servos)power.psu-5v

   Tools

   —

   Torque

   —

   Time

   —

   After

   02

   Source

   huggingface.co

6. Fabrication
   06

   Remove supports

   Scrape the plates off the bed with a putty knife and lever the support material out with a small screwdriver. Clear every screw hole and servo pocket.

   CHECKAn STS3215 drops into each servo pocket without force and every M2/M3 hole is clear of support.

   Parts in

   —

   Tools

   Putty knife, Small flat screwdriver

   Torque

   —

   Time

   —

   After

   04

   Source

   huggingface.co

7. Motor setup
   07

   Set follower motor IDs and baudrate

   Safety · human-verified required

   `lerobot-setup-motors --robot.type=so101_follower --robot.port=<follower port>`. The script asks for one motor at a time, starting with 'gripper': connect only that servo to the board with a 3-pin cable (no daisy chain), press Enter, then move on to wrist_roll, wrist_flex, elbow_flex, shoulder_lift and shoulder_pan. IDs are written to EEPROM, so this is done once.

   CHECKThe script prints `'gripper' motor id set to 6` and so on down to shoulder_pan = 1 with no communication error. Write the ID on each servo label.

   This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

   Parts in

   • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001

   Tools

   —

   Torque

   —

   Time

   —

   After

   05, 03

   Source

   huggingface.co

8. 08

   Set leader motor IDs and baudrate

   Safety · human-verified required

   `lerobot-setup-motors --teleop.type=so101_leader --teleop.port=<leader port>`. Same one-at-a-time procedure, but connect the servo with the right gear ratio for each prompt: gripper, wrist_roll and wrist_flex = 1/147; elbow_flex = 1/191; shoulder_lift = 1/345; shoulder_pan = 1/191.

   CHECKIDs 6 to 1 are set without error and each ID matches the gear-ratio label (ID 1 and 3 on C044, ID 2 on C001, IDs 4-6 on C046).

   This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

   Parts in

   • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
   • Feetech STS3215 servo, 7.4 V, 1/191 gear (C044): leader joints 1 (shoulder pan) and 3 (elbow flex)actuator.sts3215-c044
   • Feetech STS3215 servo, 7.4 V, 1/147 gear (C046): leader joints 4 (wrist flex), 5 (wrist roll), 6 (gripper)actuator.sts3215-c046

   Tools

   —

   Torque

   —

   Time

   —

   After

   05, 03

   Source

   huggingface.co

9. Follower arm
   09

   Joint 1: base, shoulder pan motor and shoulder part

   Fit a 3-pin cable into each motor as you place it. Install both horns on motor 1 (top horn with an M3x6 screw, bottom horn without screw). Place it in the base and fix with 4 M2x6 (two top, two bottom). Slide on the first motor holder and fix with 2 M2x6. Attach the shoulder part with 4 M3x6 on top and 4 M3x6 underneath, then add the shoulder motor holder.

   CHECKThe shoulder rotates smoothly by hand through the full pan range with no rubbing, and the motor 1 cable exits toward the driver-board side.

   Parts in

   • Precision screwdriver set with Phillips #0 and #1other.screwdriver-set
   • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
   • Base_SO101 (arm base, clamps to the table)printed.base
   • Base_motor_holder_SO101 (motor 1 holder)printed.base-motor-holder
   • Rotation_Pitch_SO101 (shoulder part)printed.rotation-pitch
   • Motor_holder_SO101_Base (shoulder motor holder)printed.motor-holder-base

   Tools

   Phillips #0, Phillips #1

   Torque

   —

   Time

   —

   After

   06, 07

   Source

   huggingface.co

10. Leader arm
    10

    Leader joints 1-5 with the mixed-ratio motors

    Repeat the follower joint 1 to 5 procedure (same screws) with the leader motors: joint 1 = C044 (1/191), joint 2 = C001 (1/345), joint 3 = C044 (1/191), joints 4 and 5 = C046 (1/147). Unlike the SO-100, no gears are removed from any SO-101 servo.

    CHECKHolding the leader by the wrist and letting go, the arm stays roughly where it is left instead of dropping, and each joint can be back-driven with light finger force.

    Parts in

    • Feetech STS3215 servo, 7.4 V, 1/191 gear (C044): leader joints 1 (shoulder pan) and 3 (elbow flex)actuator.sts3215-c044
    • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
    • Feetech STS3215 servo, 7.4 V, 1/147 gear (C046): leader joints 4 (wrist flex), 5 (wrist roll), 6 (gripper)actuator.sts3215-c046
    • Base_SO101 (arm base, clamps to the table)printed.base
    • Base_motor_holder_SO101 (motor 1 holder)printed.base-motor-holder
    • Rotation_Pitch_SO101 (shoulder part)printed.rotation-pitch
    • Motor_holder_SO101_Base (shoulder motor holder)printed.motor-holder-base
    • Upper_arm_SO101printed.upper-arm
    • Under_arm_SO101 (forearm)printed.under-arm
    • Motor_holder_SO101_Wrist (motor 4 holder)printed.motor-holder-wrist
    • Wrist_Roll_Pitch_SO101 (wrist holder for motor 5)printed.wrist-roll-pitch

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    06, 08

    Source

    huggingface.co

11. Follower arm
    11

    Joints 2 and 3: shoulder lift, upper arm, elbow, forearm

    Motor 2: horns on (top M3x6 horn screw), slide in from the top, fix with 4 M2x6, attach the upper arm with 4 M3x6 per side. Motor 3: horns on, insert and fix with 4 M2x6, connect the forearm with 4 M3x6 per side. Daisy-chain the 3-pin cables 1-2-3 as you go.

    CHECKShoulder lift and elbow move freely by hand over their range with no cable pinched between printed parts.

    Parts in

    • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
    • Upper_arm_SO101printed.upper-arm
    • Under_arm_SO101 (forearm)printed.under-arm

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    09

    Source

    huggingface.co

12. Leader arm
    12

    Leader holder, handle, gripper motor and trigger

    Mount the leader holder on the wrist with 4 M3x6. Attach the handle with 1 M2x6. Insert the gripper motor (1/147), fix with 2 M2x6 per side and fit a horn with an M3x6 horn screw. Attach the trigger with 4 M3x6. Chain all six motors and mount the driver board on its plate.

    CHECKSqueezing the trigger turns the gripper motor over its travel and it springs back without catching; all six leader motors are chained to the board.

    Parts in

    • Feetech STS3215 servo, 7.4 V, 1/147 gear (C046): leader joints 4 (wrist flex), 5 (wrist roll), 6 (gripper)actuator.sts3215-c046
    • Wrist_Roll_SO101 (leader holder, leader only)printed.leader-wrist-roll
    • Handle_SO101 (leader only)printed.leader-handle
    • Trigger_SO101 (leader only)printed.leader-trigger
    • WaveShare_Mounting_Plate_SO101 (or Seeedstudio_Mounting_Plate_SO101 to match your board; print one type only)printed.driver-plate
    • Motor control board: Waveshare serial bus servo driver (USB-C), one per armelectronics.bus-servo-adapter

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    10

    Source

    huggingface.co

13. Follower arm
    13

    Joints 4 and 5: wrist flex and wrist roll

    Motor 4: horns on, slide over motor holder 4, slide in motor 4 and fix with 4 M2x6. Motor 5: insert into the wrist holder with 2 front M2x6, fit only one horn (M3x6 horn screw), then fix the wrist to motor 4 with 4 M3x6 on both sides.

    CHECKWrist flex and wrist roll turn by hand without binding; cables 3-4-5 are connected.

    Parts in

    • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
    • Motor_holder_SO101_Wrist (motor 4 holder)printed.motor-holder-wrist
    • Wrist_Roll_Pitch_SO101 (wrist holder for motor 5)printed.wrist-roll-pitch

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    11

    Source

    huggingface.co

14. Calibration
    14

    Calibrate the leader

    `lerobot-calibrate --teleop.type=so101_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm`. Same procedure: middle pose, Enter, sweep every joint through its range, Enter. Reuse exactly the same ids later; the id selects the calibration file.

    CHECKA leader calibration JSON is written and re-running the command offers to reuse it instead of recalibrating.

    Parts in

    • Table clamp, 4 pcs (holds both arm bases to the table edge)other.table-clamps

    Tools

    —

    Torque

    —

    Time

    —

    After

    12

    Source

    huggingface.co

15. Follower arm
    15

    Follower gripper, driver board and wiring

    Attach the gripper to the motor 5 horn with 4 M3x6. Insert the gripper motor and fix with 2 M2x6 per side, fit both horns (top M3x6), then the moving jaw with 4 M3x6 per side. Chain cable 5-6, connect motor 1 to the board and mount the board on its plate at the base.

    CHECKThe jaw opens and closes fully by hand, and every motor is in a single daisy chain from ID 1 at the board to ID 6 at the gripper.

    Parts in

    • Feetech STS3215 servo, 7.4 V, 1/345 gear (C001): all 6 follower joints + leader joint 2 (shoulder lift)actuator.sts3215-c001
    • Wrist_Roll_Follower_SO101 (static gripper jaw, follower only)printed.follower-wrist-roll
    • Moving_Jaw_SO101 (follower only)printed.follower-moving-jaw
    • WaveShare_Mounting_Plate_SO101 (or Seeedstudio_Mounting_Plate_SO101 to match your board; print one type only)printed.driver-plate
    • Motor control board: Waveshare serial bus servo driver (USB-C), one per armelectronics.bus-servo-adapter

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    13

    Source

    huggingface.co

16. Calibration
    16

    Calibrate the follower

    Safety · human-verified required

    Clamp the base to the table edge. `lerobot-calibrate --robot.type=so101_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm`. Move the arm to the middle of every joint's range (pose shown in the terminal diagram and the calibration video) and press Enter, then move every joint except wrist_roll through its full range and press Enter. Wrist roll is treated as a full-turn joint (0-4095).

    CHECKThe live min/max table shows each joint's range growing as you move it, and a JSON named after the robot id is written under `~/.cache/huggingface/lerobot/calibration/`.

    This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

    Parts in

    • Table clamp, 4 pcs (holds both arm bases to the table edge)other.table-clamps

    Tools

    —

    Torque

    —

    Time

    —

    After

    15

    Source

    huggingface.co

17. First motion
    17

    First motion: leader-follower teleoperation

    Safety · human-verified required

    Clamp both arms, clear the follower's reach and keep a hand on its power plug. `lerobot-teleoperate --robot.type=so101_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm --teleop.type=so101_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm`. Start with slow leader moves. The follower config also accepts `--robot.max_relative_target=<n>` to cap per-step motion.

    CHECKThe follower tracks the leader joint for joint in the same direction, the gripper follows the trigger, and nothing hits a hard stop at the range ends.

    This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

    Parts in

    • Table clamp, 4 pcs (holds both arm bases to the table edge)other.table-clamps

    Tools

    —

    Torque

    —

    Time

    —

    After

    16, 14

    Source

    huggingface.co

18. Cameras
    18

    Cameras (optional): mount and check streams

    Swap the follower Wrist_Roll for the wrist-camera version (move the gripper servo across, 6 M3 screws to the servo and 4 to the next joint) and fix the camera module with 4 of the spare M2 servo screws. Mount the overhead camera on its printed stand. Run `lerobot-find-cameras opencv` to list indices, then teleoperate with `--robot.cameras="{front: {type: opencv, index_or_path: 0, width: 640, height: 480, fps: 30}}" --display_data=true`.

    CHECK`lerobot-find-cameras opencv` lists each camera, and the rerun viewer shows every stream updating at about 30 fps with joint plots during teleoperation.

    Parts in

    • Wrist camera (optional): 32x32 mm USB UVC camera module, min 720p / 30 fpssensor.wrist-camera-optional
    • Overhead / scene camera (optional): USB webcamsensor.scene-camera-optional
    • Wrist camera mount (optional): Wrist_Cam_Mount_32x32_UVC_Module_SO101.stl, replaces the follower Wrist_Rollprinted.wrist-cam-mount-optional
    • Overhead webcam mount set (optional): arm_base, cam_mount_bottom, cam_mount_topprinted.overhead-cam-mount-optional

    Tools

    Phillips #0, Phillips #1

    Torque

    —

    Time

    —

    After

    17

    Source

    huggingface.co

19. Policy
    19

    Record a dataset

    `hf auth login --token ${HUGGINGFACE_TOKEN} --add-to-git-credential`, `HF_USER=$(NO_COLOR=1 hf auth whoami | awk -F': *' 'NR==1 {print $2}')`, then `lerobot-record --robot.type=so101_follower --robot.port=<port> --robot.id=my_awesome_follower_arm --robot.cameras="{ front: {type: opencv, index_or_path: 0, width: 1920, height: 1080, fps: 30}}" --teleop.type=so101_leader --teleop.port=<port> --teleop.id=my_awesome_leader_arm --display_data=true --dataset.repo_id=${HF_USER}/record-test --dataset.num_episodes=5 --dataset.single_task="Grab the black cube"`. Right arrow / `n` ends an episode, left arrow / `r` re-records, Esc / `q` stops. Upstream suggests at least 50 episodes (10 per object location) for a real task.

    CHECKThe end-of-run cadence summary reports close to 30 Hz, and the dataset appears at `https://huggingface.co/datasets/${HF_USER}/record-test` and replays with `lerobot-replay --robot.type=so101_follower ... --dataset.repo_id=${HF_USER}/record-test --dataset.episode=0`.

    Parts in

    —

    Tools

    Hugging Face account with a write token

    Torque

    —

    Time

    —

    After

    18

    Source

    huggingface.co

20. 20

    Train ACT (or fine-tune SmolVLA)

    ACT: `lerobot-train --dataset.repo_id=${HF_USER}/so101_test --policy.type=act --output_dir=outputs/train/act_so101_test --job_name=act_so101_test --policy.device=cuda --wandb.enable=true --policy.repo_id=${HF_USER}/my_policy`. SmolVLA: `lerobot-train --policy.path=lerobot/smolvla_base --dataset.repo_id=${HF_USER}/mydataset --batch_size=64 --steps=20000 ...` (about 4 h on one A100 per the docs). No local GPU: add `--job.target=a10g-small` to run on Hugging Face Jobs.

    CHECKCheckpoints appear under `outputs/train/act_so101_test/checkpoints/` and the training loss curve has flattened; the final model is pushed to `${HF_USER}/my_policy`.

    Parts in

    —

    Tools

    NVIDIA GPU (CUDA) or Apple silicon (mps), or HF Jobs / Colab

    Torque

    —

    Time

    —

    After

    19

    Source

    huggingface.co

21. 21

    Run the policy on the arm

    Safety · human-verified required

    `lerobot-rollout --strategy.type=base --policy.path=${HF_USER}/my_policy --robot.type=so101_follower --robot.port=<port> --robot.id=my_awesome_follower_arm --robot.cameras="<same camera names and settings as the dataset>" --task="Grab the black cube" --duration=60`. Use `--strategy.type=sentry --dataset.repo_id=${HF_USER}/eval_so101` to record evaluation episodes; add `--inference.type=rtc` for slow VLA policies. Keep a hand on the power plug.

    CHECKThe follower reaches for the object within a few seconds of start and completes the task in most trials from the positions seen in training.

    This step can hurt a person or ruin parts. Its instructions need sign-off by a human who has done it before relying on them. Stop and ask if anything differs from what you see.

    Parts in

    • Table clamp, 4 pcs (holds both arm bases to the table edge)other.table-clamps

    Tools

    —

    Torque

    —

    Time

    —

    After

    20

    Source

    huggingface.co

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