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Build package

Build SO-100 (SO-ARM100)

The Robot Studio / Hugging Face · Arm · discontinued

Original Standard Open Arm 100: a 3D-printable 6-DOF low-cost arm that served as the first reference hardware for LeRobot; superseded by the SO-101.

L2Sim-verifiedGate: Loads in browser and GPU sim, mass within tolerance of the BOM, holds a stand. Unlocks .training.

Build is partial: Discontinued; files public, parts may be hard to source.

Two ways to get SO-100 (SO-ARM100)

Compare all →
  1. 1Source parts, print the rest$244+US cart · 6/8 lines priced
  2. 2Hire a builderRequesthumanoidrobots.team/therobotstudio/so-100
Fig 1/6RenderSO-100 (SO-ARM100) studio render, three-quarter front view
Studio render of the published MJCF, keyframe pose from the model. Geometry only; colours are the model's own materials.© Rendered by Hyperspawn from mujoco_menagerie/trs_so_arm100 (Apache-2.0) · Hyperspawn render · source
Drawing
/therobotstudio/so-100
Maker
The Robot Studio / Hugging Face
Country
FR
Package rev
v0.1.0
Level
L2 Sim-verified
Availability
DIY
Openness
100/100
HW licence
Apache-2.0
Last checked
2026-09-25
DOF
6
Actuators
Feetech STS3215 serial bus servos

'discontinued' = superseded by SO-101 in the same repo (SO100.md kept); files remain available for DIY.

01

Configure

Saved in the URL. Share the link to share the build.
Region · where parts ship to
Printer bed (square, mm)
Printed parts
Estimate for United States
$244+ 2 unpriced lines: lower bound
Cart $244
02

Source

One cart across 3 vendors · prices in USD as listed

8 lines · 21 parts · 0 without an offer in US · 6/8 lines sourced in 2+ regions (L3 gate)

#PartCategoryQtyUnitLineOffer
Alibaba (6-pack)1 line · $180.00
1
Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)
actuator.sts3215 · MPN STS3215 · 2 alt
actuator12$15.00list price$180.00Alibaba (6-pack)
Amazon6 lines · $64.00 + 1 unpriced
2
Motor control board: Waveshare serial bus servo driver (USB-C), one per arm
electronics.bus-servo-adapter
electronics2$11.00list price$22.00Amazon
3
USB-C cable, 2-pack
cable.usb-c
cable1$7.00list price$7.00Amazon
4
DC power supply, 5 V, 5.5x2.1 mm barrel (one per arm)
power.psu-5v
power2$10.00list price$20.00Amazon
5
Table clamp, 4 pcs
other.table-clamps
other1$9.00list price$9.00Amazon
6
Precision screwdriver set (Phillips)
other.screwdriver-set
other1$6.00list price$6.00Amazon
7
Overhead / scene camera (optional): USB webcam
sensor.scene-camera-optional
sensor1unpriced—AmazonRecommended model in the overhead webcam mount guide (written for the SO-100)
Amazon (innomaker)1 line · unpriced
8
Wrist camera (optional): 32x32 mm USB UVC camera module, min 720p / 30 fps
sensor.wrist-camera-optional
sensor1unpriced—Amazon (innomaker)Recommended model in the SO-100/SO-101 wrist-mount guide
Cart total · US21$244.002 lines unpriced, not in total
03

Fabricate

Planned for a 256 mm bed
Fabricated parts
5
Print time (sum)
—
Material (sum)
—
Plates · estimate
—

No plate estimate: the package does not list grams per part yet, and we will not guess them. Slice the source files for your 256 mm bed.

PartProcessMaterialQtyh / partg / partProfile
Follower part plate, SO_ARM100_08k (Print_Follower_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Follower_Bambu_P1P.3mf)
printed.follower-plate
FDMPLA1——0.4 mm nozzle at 0.2 mm layers (or 0.6 mm nozzle at 0.4 mm); 13% infill; supports everywhere except slopes steeper than 45°; no supports in horizontal screw holes. 12 individual follower STLs in STL/SO100/Individual/Follower.
Leader part plate, SO_ARM100_08k (Print_Leader_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Leader_Bambu_P1P.3mf), includes handle and trigger
printed.leader-plate
FDMPLA1——Same as the follower plate. 13 individual leader STLs in STL/SO100/Individual/Leader.
Fit gauges: Gauge_0 + Gauge_tight_1 (STS3215) or the two Lego size tests
printed.gauges
FDMPLA2——source
Wrist camera mount (optional): Wrist_Cam_Mount_32x32_UVC_Module_SO100.stl, replaces the follower Wrist_Roll
printed.wrist-cam-mount-optional
FDMPLA1——source
PLA · 5 parts · g unknown
04

Assemble

Every step ends in a check
Steps
13
Subassemblies
8
Hands-on time (sum)
—
Critical path
—
Your progress · this device
—

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

Assembly graph · lanes are subassemblies, columns are dependency depthcritical pathdonesafety
D0D1D2D3D4D5D6D7D8Fabrication1 stepsSoftware1 stepsMotor setup3 stepsLeader arm2 stepsFollower arm3 stepsCalibration1 stepsFirst motion1 stepsPolicy1 steps1. Check printer fit, then print both plates01Check printer fi…2. Install LeRobot with the Feetech SDK02Install LeRobot …3. Power the boards and find each arm's port03Power the boards…4. Set follower motor IDs before assembly04Set follower mot…5. Set leader motor IDs before assembly05Set leader motor…6. Remove the gears from the 6 leader servos06Remove the gears…7. Follower motors 1-2: base and shoulder07Follower motors …8. Follower motors 3-5: elbow, wrist flex, wrist roll08Follower motors …9. Leader arm: motors 1-5, holder, handle, trigger09Leader arm: moto…10. Follower gripper and controller10Follower gripper…11. Calibrate follower and leader11Calibrate follow…12. First motion: teleoperate12First motion: te…13. Record, train and run a policy13Record, train an…

Steps, in build order

  1. Fabrication
    01

    Check printer fit, then print both plates

    Print Gauge_0 and test it against an STS3215 or a Lego brick. Then print the follower and leader plates for your bed (Ender 220x220, Prusa/UP 205x250, Bambu A1 mini in two parts, or the Bambu P1P .3mf) at 0.2 mm layers, 13% infill, PLA. Remove all supports with a small screwdriver.

    CHECKA servo slides snugly into Gauge_0, and every servo pocket and screw hole on the printed parts is free of support material.
    Parts in
    • Fit gauges: Gauge_0 + Gauge_tight_1 (STS3215) or the two Lego size testsprinted.gauges
    • Follower part plate, SO_ARM100_08k (Print_Follower_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Follower_Bambu_P1P.3mf)printed.follower-plate
    • Leader part plate, SO_ARM100_08k (Print_Leader_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Leader_Bambu_P1P.3mf), includes handle and triggerprinted.leader-plate
    Tools
    FDM printer, 220x220 mm bed or larger, PLA filament, Putty knife
    Torque
    —
    Time
    —
    After
    Start
  2. Software
    02

    Install LeRobot with the Feetech SDK

    `conda create -y -n lerobot python=3.12 && conda activate lerobot`, clone https://github.com/huggingface/lerobot, then `pip install -e ".[feetech]"`.

    CHECK`lerobot-setup-motors --help` prints its usage.
    Parts in
    —
    Tools
    —
    Torque
    —
    Time
    —
    After
    Start
  3. Motor setup
    03

    Power the boards and find each arm's port

    Safety · human-verified required

    Set the Waveshare jumpers to channel `B` (USB), connect the 5 V supply and USB-C, run `lerobot-find-port` and unplug when prompted. Repeat for the second board. On Linux you may need `sudo chmod 666 /dev/ttyACM0 /dev/ttyACM1`.

    CHECKEach board reports its own port (e.g. `/dev/ttyACM0` and `/dev/ttyACM1`).

    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-packcable.usb-c
    • DC power supply, 5 V, 5.5x2.1 mm barrel (one per arm)power.psu-5v
    Tools
    —
    Torque
    —
    Time
    —
    After
    02
  4. 04

    Set follower motor IDs before assembly

    Safety · human-verified required

    Unlike the SO-101, SO-100 connectors are hard to reach once assembled, so do this first. `lerobot-setup-motors --robot.type=so100_follower --robot.port=<follower port>`. Connect one servo at a time when prompted (gripper first, then wrist_roll, wrist_flex, elbow_flex, shoulder_lift, shoulder_pan).

    CHECKThe script prints `'gripper' motor id set to 6` through shoulder_pan = 1. Label each servo with its ID.

    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 (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    Tools
    —
    Torque
    —
    Time
    —
    After
    03
  5. 05

    Set leader motor IDs before assembly

    Safety · human-verified required

    `lerobot-setup-motors --teleop.type=so100_leader --teleop.port=<leader port>` with the same one-servo-at-a-time procedure on the six leader servos.

    CHECKIDs 6 to 1 are set without communication errors, and the six leader servos are labelled separately from the follower ones.

    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 (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    Tools
    —
    Torque
    —
    Time
    —
    After
    03
  6. Leader arm
    06

    Remove the gears from the 6 leader servos

    Open each leader servo case and remove the gear train as shown in the 'Video removing gears' on the SO-100 docs page, then close the case. The servo then acts only as a position encoder, so the leader can be moved by hand. When fitting horns later, try not to turn the output: without gears it spins freely.

    CHECKEach leader servo output turns freely by hand, and the ID set in the previous step still reads back (re-run setup for that motor if not).
    Parts in
    • Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    Tools
    Phillips #0
    Torque
    —
    Time
    —
    After
    05
  7. Follower arm
    07

    Follower motors 1-2: base and shoulder

    Insert two 3-pin wires into motor 1, place it in the base and fix with 4 screws (two top, two bottom). Slide on the first motor holder (2 screws), fit both horns (top horn screw), route one wire to the back and one to the left, attach the shoulder with 4 screws top and 4 bottom. Slide in motor 2 from the top and link the wire from motor 1. Add the shoulder motor holder (tight fit: wire 1-2 behind it, the other wire up), fix motor 2 with 4 screws, fit its horns, install the base attachment with 2 screws and the upper arm with 4 screws per side.

    CHECKShoulder pan and shoulder lift move by hand without pinching the 1-2 cable behind the holder.
    Parts in
    • Precision screwdriver set (Phillips)other.screwdriver-set
    • Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    • Follower part plate, SO_ARM100_08k (Print_Follower_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Follower_Bambu_P1P.3mf)printed.follower-plate
    Tools
    Phillips #0, Phillips #1
    Torque
    —
    Time
    —
    After
    01, 04
  8. 08

    Follower motors 3-5: elbow, wrist flex, wrist roll

    Route the cable from motor 2 through the cable holder to motor 3, fix with 4 screws, fit horns and connect the forearm with 4 screws per side. Slide in motor 4, connect the cable from motor 3 and screw it in its holder, fit motor holder 4 (tight; one wire up, the one from motor 3 down), fix with 4 screws and fit horns. Insert motor 5 in the wrist holder (2 front screws), connect 4-5 and pre-insert the gripper wire, fix the wrist to motor 4 with 4 screws per side, fit one horn on motor 5.

    CHECKElbow and both wrist joints move by hand with cables 2-3, 3-4 and 4-5 connected and not stretched at the range ends.
    Parts in
    • Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    • Follower part plate, SO_ARM100_08k (Print_Follower_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Follower_Bambu_P1P.3mf)printed.follower-plate
    Tools
    Phillips #0, Phillips #1
    Torque
    —
    Time
    —
    After
    07
  9. Leader arm
    09

    Leader arm: motors 1-5, holder, handle, trigger

    Repeat follower steps 1-23 with the de-geared leader servos. Then mount the leader holder on the wrist (1 screw), attach the handle to motor 5 (4 screws), insert the gripper motor (3 screws per side, horn screw, connect the wire), attach the trigger (4 screws) and mount the controller on the back.

    CHECKEvery leader joint moves with light finger force and the trigger turns the gripper servo output.
    Parts in
    • Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    • Leader part plate, SO_ARM100_08k (Print_Leader_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Leader_Bambu_P1P.3mf), includes handle and triggerprinted.leader-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
    01, 06
  10. Follower arm
    10

    Follower gripper and controller

    Attach the gripper to motor 5, insert the gripper motor, connect 5-6 and fix with 3 screws per side. Fit the horns (horn screw) and the claw with 4 screws per side. Mount the motor controller on the back of the base.

    CHECKThe claw opens and closes by hand, and the chain runs from the board to ID 1 and on to ID 6.
    Parts in
    • Feetech STS3215 servo, 7.4 V (6 follower + 6 leader; gears are removed from the 6 leader units)actuator.sts3215
    • Follower part plate, SO_ARM100_08k (Print_Follower_SO_ARM100_08k_Ender.STL, _UP_Prusa.STL, _UP_BambuLabA1Mini_part1/part2.STL or Print_Follower_Bambu_P1P.3mf)printed.follower-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
    08
  11. Calibration
    11

    Calibrate follower and leader

    Safety · human-verified required

    Clamp both bases. `lerobot-calibrate --robot.type=so100_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm` then `lerobot-calibrate --teleop.type=so100_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm`. For each: middle-of-range pose, Enter, sweep every joint through its range, Enter. The SO-100 flow is manual; the old auto-calibration was removed upstream.

    CHECKBoth runs write a calibration JSON under `~/.cache/huggingface/lerobot/calibration/`, and the recorded ranges look plausible (no joint stuck at a single value).

    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 pcsother.table-clamps
    Tools
    —
    Torque
    —
    Time
    —
    After
    10, 09
  12. First motion
    12

    First motion: teleoperate

    Safety · human-verified required

    `lerobot-teleoperate --robot.type=so100_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm --teleop.type=so100_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm`. Clear the workspace and keep a hand on the follower power plug.

    CHECKThe follower mirrors the leader joint for joint in the same direction and the gripper follows the trigger.

    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 pcsother.table-clamps
    Tools
    —
    Torque
    —
    Time
    —
    After
    11
  13. Policy
    13

    Record, train and run a policy

    Safety · human-verified required

    Mount at least one camera. `lerobot-record --robot.type=so100_follower ... --robot.cameras="{ front: {type: opencv, index_or_path: 0, width: 640, height: 480, fps: 30}}" --teleop.type=so100_leader ... --dataset.repo_id=${HF_USER}/so100_test --dataset.num_episodes=50 --dataset.single_task="<task>"`, then `lerobot-train --dataset.repo_id=${HF_USER}/so100_test --policy.type=act --policy.device=cuda --policy.repo_id=${HF_USER}/my_policy` (or `--policy.path=lerobot/smolvla_base`), then `lerobot-rollout --strategy.type=base --policy.path=${HF_USER}/my_policy --robot.type=so100_follower --robot.port=<port> --robot.cameras="<same as dataset>" --task="<task>" --duration=60`.

    CHECKThe dataset is viewable on the Hub, training checkpoints appear under outputs/train/, and in rollout the arm attempts the recorded task from 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
    • 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_SO100.stl, replaces the follower Wrist_Rollprinted.wrist-cam-mount-optional
    Tools
    Hugging Face account, CUDA or Apple-silicon machine, or HF Jobs
    Torque
    —
    Time
    —
    After
    12

Progress is stored in this browser only (localStorage). Nothing is sent anywhere.

05

Bring-up

Flash · calibrate · first policy
  1. A

    Flash firmware

    TargetsFeetech STS3215 servo (EEPROM: ID 1-6 and baudrate via lerobot-setup-motors), Waveshare serial bus servo driver (USB bridge, no user firmware)

    Repogithub.com/huggingface/lerobot

    Stock Feetech firmware. In lerobot 0.6.x, so100_follower and so101_follower are registered to the same SOFollower config class (lerobot.robots.so_follower), so SO-100 and SO-101 followers share a driver and calibration flow. Datasets and policies recorded before lerobot 0.5 use a different joint calibration convention (see the LeRobot backward-compatibility guide).

  2. B

    Calibrate

    Calibrationlerobot-calibrate --robot.type=so100_follower --robot.port=<port> --robot.id=<id>; lerobot-calibrate --teleop.type=so100_leader --teleop.port=<port> --teleop.id=<id>. Middle pose, Enter, sweep all joints, Enter.

    Log the output. It goes in your build report.

  3. C

    First policy

    • SmolVLA base (pretrained VLA to fine-tune on your own SO-100 dataset)LeRobot (SmolVLA) source
    • SO-100/101 language-conditioned manipulation (VLA, zero-shot or fine-tune)LeRobot (MolmoAct2) source
    Run it in sim on humanoidrobots.training →

Try the policy in the browser sim before it touches hardware. Keep a hand near the power switch the first time a policy runs on the real robot.

06

Report your build

Moves SO-100 (SO-ARM100) toward L4 · Built

A build report is the only thing that proves a package works. It raises the level, puts a point on the map, and tells the Foreman which steps to rewrite.

Robot/therobotstudio/so-100

Sends JSON to POST hyperspawn.io/api/v1/reports. Reports are reviewed before they count toward L4 or appear on the map.

GATE

Level gate

Holds L2 · evidence, not confidence
  1. L0
    Indexed

    Known to exist. Atlas page only.

    • 3 sources on record(met)
    held
  2. L1
    Compiled

    Package validates against the spec; every fact has a source.

    • Build package compiled(met)
    • 16 sources across robot and package(met)
    held
  3. L2
    Sim-verified

    Loads in browser and GPU sim, mass within tolerance of the BOM, holds a stand. Unlocks .training.

    • URDF/MJCF is public(met)
    • Sim load, mass tolerance and stand are checked on .training(checked elsewhere)
    held
  4. L3
    Sourced

    Every BOM line resolves to a live offer in at least two regions. Unlocks the one-click cart.

    • 6/8 BOM lines have offers in 2+ regions(not met)
    next
  5. L4
    Built

    At least one community build report with photos and bring-up logs. Unlocks Build it as the main action.

    • 0 reviewed build reports(not met)
    • Review feed unreachable at last refresh; count is registry-only(checked elsewhere)
    locked
  6. L5
    Certified

    The robot's maintainer signs the package. Unlocks certified teams and kit sales.

    • Maintainer signature not recorded(not met)
    locked

Levels are cumulative and set by the registry from reviewed evidence. This panel shows what can be measured from the package today.

Same robot, other verbs

REV

Revisions and sources

Every fact on this sheet traces to one of these
RevDescriptionChecked
PKGBuild package, current revision 0.1.0—
S1GitHub repogithub.com2026-09-24
S2Hackster: SO-101 as next-gen of SO-100hackster.io2026-09-24
S3LeRobot SO-100 docshuggingface.co2026-09-25
S4SO-ARM100 SO100.md (BOM, print settings)github.com2026-09-25
S5SO-ARM100 README (SO-100 marked deprecated, optional hardware)github.com2026-09-25
S6STL/SO100 (plates and individual parts)github.com2026-09-25
S7STEP/SO100 CADgithub.com2026-09-25
S8SO-ARM100 CHANGELOG (SO_ARM100_08k)github.com2026-09-25
S9LeRobot docs: SO-100huggingface.co2026-09-25
S10LeRobot docs: imitation learning on real robotshuggingface.co2026-09-25
S11LeRobot docs: installationhuggingface.co2026-09-25
S12LeRobot docs: SmolVLAhuggingface.co2026-09-25
S13LeRobot docs: MolmoAct2huggingface.co2026-09-25
S14HF model: lerobot/smolvla_basehuggingface.co2026-09-25
S15HF model: lerobot/MolmoAct2-SO100_101-LeRobothuggingface.co2026-09-25
S16HF dataset: lerobot/svla_so100_pickplacehuggingface.co2026-09-25