Build Koch v1.1 Low-Cost Robot Arm

Steps

16

Subassemblies

8

Hands-on time (sum)

—

Critical path

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Your progress · this device

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

1. Fabrication
   01

   Print leader and follower parts

   Print one of each STL in `hardware/leader/STL` and `hardware/follower/STL` (the extras blocks are optional). Level and clean the bed, apply a thin even glue-stick layer, print at 0.2 mm layers or finer with a nozzle of 0.4 mm or less and about 30% infill. Scrape parts off with the putty knife, remove supports and re-apply glue before the next print.

   CHECKAn M2 screw passes through the 2.4 mm through holes without forcing, and mating holes line up when parts are held together (README footnote 7 allows about +/-0.2 mm).

   Parts in

   • Leader_Baseprinted.leader.base
   • Leader_Shoulder_To_Elbowprinted.leader.shoulder-to-elbow
   • Leader_Elbow_To_Wristprinted.leader.elbow-to-wrist
   • Leader_Elbow_To_Wrist_Extensionprinted.leader.elbow-to-wrist-extension
   • Leader_Gripper_Handleprinted.leader.gripper-handle
   • Leader_Gripper_Triggerprinted.leader.gripper-trigger
   • Leader_Platform (optional; lets the follower reach the floor)printed.leader.platform
   • Robotis_FPX330_S101 frame (printed instead of buying the Robotis FPX330-S101 set)printed.leader.fpx330-s101
   • Follower_Baseprinted.follower.base
   • Follower_Shoulder_Rotationprinted.follower.shoulder-rotation
   • Follower_Shoulder_To_Elbowprinted.follower.shoulder-to-elbow
   • Follower_Elbow_To_Wristprinted.follower.elbow-to-wrist
   • Follower_Elbow_To_Wrist_Extensionprinted.follower.elbow-to-wrist-extension
   • Follower_Gripper_Static_Partprinted.follower.gripper-static
   • Follower_Gripper_Moving_Partprinted.follower.gripper-moving

   Tools

   FDM printer (e.g. Prusa Mini+, Bambu P1, Ender 3), Glue stick, Putty knife

   Torque

   —

   Time

   —

   After

   Start

   Source

   github.com

2. Software
   02

   Install LeRobot with the Dynamixel extra

   Follow the LeRobot installation guide (`conda create -y -n lerobot python=3.12`, `conda activate lerobot`, clone huggingface/lerobot and install it), then add the Dynamixel SDK: `pip install -e ".[dynamixel]"`.

   CHECK`lerobot-find-port --help` and `lerobot-setup-motors --help` both run without an import error.

   Parts in

   —

   Tools

   Linux or macOS computer, conda (miniforge)

   Torque

   —

   Time

   —

   After

   Start

   Source

   huggingface.co

3. Follower arm
   03

   Assemble the follower arm mechanics (per video)

   Follow the follower part of the assembly video. XL430-W250-T servos go on shoulder pan and shoulder lift; XL330-M288-T on elbow, wrist flex, wrist roll and gripper. Keep the servos in the same orientation as the CAD and screw horns on in their default position. Per the LeRobot docs, do NOT plug in the motor cables and do NOT screw the controller board to the base yet; that happens after motor setup.

   CHECKEvery joint turns by hand through its range without binding and the horn marks line up with the CAD pose; no 3-pin cables are connected yet.

   Parts in

   • Dynamixel XL430-W250-T servo (follower shoulder pan + shoulder lift, 12 V)actuator.follower.xl430-w250-t
   • Dynamixel XL330-M288-T servo (follower elbow, wrist flex, wrist roll, gripper; 5 V)actuator.follower.xl330-m288-t
   • XL330 frame and idler wheel set FPX330-H101, 4 pcs (follower; 3 of 4 used)structure.follower.fpx330-h101
   • XL430 idler wheel set HN11-I101 (follower)structure.follower.hn11-i101
   • Follower_Baseprinted.follower.base
   • Follower_Shoulder_Rotationprinted.follower.shoulder-rotation
   • Follower_Shoulder_To_Elbowprinted.follower.shoulder-to-elbow
   • Follower_Elbow_To_Wristprinted.follower.elbow-to-wrist
   • Follower_Elbow_To_Wrist_Extensionprinted.follower.elbow-to-wrist-extension
   • Follower_Gripper_Static_Partprinted.follower.gripper-static
   • Follower_Gripper_Moving_Partprinted.follower.gripper-moving

   Tools

   1.5 mm cruciform screwdriver

   Torque

   —

   Time

   —

   After

   01

   Source

   youtube.com

4. Leader arm
   04

   Assemble the leader arm mechanics (per video)

   Follow the leader part of the assembly video: six XL330-M077-T servos, the gripper is replaced by a handle and trigger. As for the follower, leave motor cables unplugged and the controller board unscrewed until motor setup is done.

   CHECKAll six leader joints and the trigger move freely by hand; handle and trigger are firmly attached to the last servo.

   Parts in

   • Dynamixel XL330-M077-T servo (leader arm, 5 V)actuator.leader.xl330-m077-t
   • XL330 frame and idler wheel set FPX330-H101, 4 pcs (leader; 3 of 4 used)structure.leader.fpx330-h101
   • Leader_Baseprinted.leader.base
   • Leader_Shoulder_To_Elbowprinted.leader.shoulder-to-elbow
   • Leader_Elbow_To_Wristprinted.leader.elbow-to-wrist
   • Leader_Elbow_To_Wrist_Extensionprinted.leader.elbow-to-wrist-extension
   • Leader_Gripper_Handleprinted.leader.gripper-handle
   • Leader_Gripper_Triggerprinted.leader.gripper-trigger
   • Robotis_FPX330_S101 frame (printed instead of buying the Robotis FPX330-S101 set)printed.leader.fpx330-s101

   Tools

   1.5 mm cruciform screwdriver

   Torque

   —

   Time

   —

   After

   01

   Source

   youtube.com

5. Electronics
   05

   Find the USB port of each controller board

   Plug both boards into the computer by USB-C and run `lerobot-find-port`. Unplug the board it asks about and press Enter; it prints that board's port. On Linux grant access with `sudo chmod 666 /dev/ttyACM0` (and ACM1). On the Waveshare board set both jumpers to channel B (USB).

   CHECK`lerobot-find-port` prints a distinct port for each arm (e.g. `/dev/ttyACM0` leader, `/dev/ttyACM1` follower) and the result is reproducible after re-plugging.

   Parts in

   • Waveshare Serial Bus Servo Driver Board (leader, run at 5 V)electronics.leader.servo-driver
   • Waveshare Serial Bus Servo Driver Board (follower, 12 V)electronics.follower.servo-driver
   • USB C-A or C-C cable, 2 pcs set (one cable per arm; shared)cable.usb-c

   Tools

   —

   Torque

   —

   Time

   —

   After

   02

   Source

   huggingface.co

6. Leader arm
   06

   Fasten the Leader_Platform to the Leader_Base

   The platform is now screwed, not snapped, in place (the video is outdated here). Insert four M2 nuts into the pockets under the Leader_Platform, then fasten it to the Leader_Base with four M2x5 screws. If the Waveshare board is already mounted, remove it temporarily to reach the two screws beneath it.

   CHECKThe platform does not rock or lift when you press on either end, and all four screws are tight in their nuts.

   Parts in

   • Leader_Platform (optional; lets the follower reach the floor)printed.leader.platform
   • M2x5 machine screw (Leader_Platform to Leader_Base)fastener.leader.m2x5
   • M2 nut (pockets under Leader_Platform)fastener.leader.m2-nut

   Tools

   1.5 mm cruciform screwdriver

   Torque

   —

   Time

   —

   After

   04

   Source

   github.com

7. Electronics
   07

   Follower power wiring: 12 V board and 12 V to 5 V reducer

   Safety · human-verified required

   Per the v1.1 wiring diagram: the driver board's V/G/D port feeds the two XL430-W250-T servos at 12 V. The EP-JY-DC5 reducer takes 12 V IN+/GND IN- from the board's V/G pins via jumper wires and its OUT+ 5 V / OUT- GND, together with the board's D (data) pin, feed the XL330-M288-T chain. The v1.1 reducer needs no soldering or trimming (README change 3). Do not connect any XL330 to a 12 V line.

   CHECKWith the 12 V supply on and no servos connected, the multimeter reads about 12 V at the board's V/G pins and about 5 V at the reducer output, with correct polarity.

   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

   • Waveshare Serial Bus Servo Driver Board (follower, 12 V)electronics.follower.servo-driver
   • 12 V to 5 V voltage reducer (feeds the four XL330 servos)power.follower.voltage-reducer
   • 12 V DC power supply (follower arm)power.follower.psu-12v
   • Jumper wires, 3 x 40 pcs set (M-M, M-F, F-F) (follower)cable.follower.jumpers

   Tools

   Digital multimeter

   Torque

   —

   Time

   —

   After

   03

   Source

   github.com

8. Follower arm
   08

   Set follower motor IDs and baudrate

   Safety · human-verified required

   Run `lerobot-setup-motors --robot.type=koch_follower --robot.port=<follower port>`. When prompted, connect ONLY the named motor straight to the board (starting with 'gripper', then 'wrist_roll', and so on down to 'shoulder_pan') and press Enter; each motor's ID and baudrate are written to EEPROM once. The LeRobot page says to power the board from the 5 V supply for this step. That matters: the XL330-M288-T is rated 3.7-6.0 V, so never plug an XL330 directly into the board while it is on 12 V (XL430-W250-T is rated 6.5-12.0 V, Robotis e-Manual).

   CHECKThe script prints `'gripper' motor id set to 6` and so on down to shoulder_pan with id 1, then exits without a communication error.

   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

   • Dynamixel XL430-W250-T servo (follower shoulder pan + shoulder lift, 12 V)actuator.follower.xl430-w250-t
   • Dynamixel XL330-M288-T servo (follower elbow, wrist flex, wrist roll, gripper; 5 V)actuator.follower.xl330-m288-t
   • Waveshare Serial Bus Servo Driver Board (follower, 12 V)electronics.follower.servo-driver
   • 5 V DC power supply (leader arm)power.leader.psu-5v

   Tools

   —

   Torque

   —

   Time

   —

   After

   05, 03

   Source

   huggingface.co

9. Leader arm
   09

   Set leader motor IDs and baudrate

   Safety · human-verified required

   Power the leader board from the 5 V supply only (README footnote 14: 5 V on a board rated 9-12.6 V is intended, the XL330-M077 are 5 V servos). Run `lerobot-setup-motors --teleop.type=koch_leader --teleop.port=<leader port>` and connect one motor at a time as prompted.

   CHECKAll six leader motors report their new IDs (gripper 6 down to shoulder_pan 1) and the script finishes cleanly.

   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

   • Dynamixel XL330-M077-T servo (leader arm, 5 V)actuator.leader.xl330-m077-t
   • Waveshare Serial Bus Servo Driver Board (leader, run at 5 V)electronics.leader.servo-driver
   • 5 V DC power supply (leader arm)power.leader.psu-5v

   Tools

   —

   Torque

   —

   Time

   —

   After

   05, 04

   Source

   huggingface.co

10. Follower arm
    10

    Daisy-chain follower motors and mount its board

    Plug each motor's 3-pin cable into the next one, connect shoulder_pan (id 1) to the board, then screw the board and reducer to Follower_Base. Clamp the base to the table.

    CHECKCables do not pull tight at any joint limit when you move the unpowered arm through its range, and the base does not move on the table.

    Parts in

    • Waveshare Serial Bus Servo Driver Board (follower, 12 V)electronics.follower.servo-driver
    • Table clamp (follower)other.follower.table-clamp
    • 1.5 mm star/cruciform precision screwdriver, 2 pcs set (shared by both arms)other.screwdriver-1-5mm

    Tools

    —

    Torque

    —

    Time

    —

    After

    08, 07

    Source

    huggingface.co

11. Leader arm
    11

    Daisy-chain leader motors and mount its board

    Chain the six leader motors, connect shoulder_pan to the board, screw the board to the Leader_Base and clamp the leader to the table next to the follower.

    CHECKThe leader moves freely through its range with cables attached and the trigger returns without catching on a cable.

    Parts in

    • Waveshare Serial Bus Servo Driver Board (leader, run at 5 V)electronics.leader.servo-driver
    • Jumper wires, 3 x 40 pcs set (M-M, M-F, F-F) (leader)cable.leader.jumpers
    • Table clamp (leader)other.leader.table-clamp

    Tools

    —

    Torque

    —

    Time

    —

    After

    09, 06

    Source

    huggingface.co

12. Calibration
    12

    Calibrate the follower

    Safety · human-verified required

    Run `lerobot-calibrate --robot.type=koch_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm`. Move every joint to the middle of its range and press Enter, then move each joint through its full range of motion. Same procedure as SO-100/SO-101.

    CHECKThe script shows a min/pos/max table where each joint's range spans its physical travel, and writes a calibration file named after the robot 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

    • Dynamixel XL430-W250-T servo (follower shoulder pan + shoulder lift, 12 V)actuator.follower.xl430-w250-t
    • Dynamixel XL330-M288-T servo (follower elbow, wrist flex, wrist roll, gripper; 5 V)actuator.follower.xl330-m288-t

    Tools

    —

    Torque

    —

    Time

    —

    After

    10

    Source

    huggingface.co

13. 13

    Calibrate the leader

    Run `lerobot-calibrate --teleop.type=koch_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm` and repeat the middle-of-range then full-range procedure.

    CHECKThe calibration file for the leader id is written and the range table covers each joint's travel, including the trigger.

    Parts in

    • Dynamixel XL330-M077-T servo (leader arm, 5 V)actuator.leader.xl330-m077-t

    Tools

    —

    Torque

    —

    Time

    —

    After

    11

    Source

    huggingface.co

14. First motion
    14

    First motion: leader-follower teleoperation

    Safety · human-verified required

    Clear the follower's workspace, then run `lerobot-teleoperate --robot.type=koch_follower --robot.port=<follower port> --robot.id=my_awesome_follower_arm --teleop.type=koch_leader --teleop.port=<leader port> --teleop.id=my_awesome_leader_arm`. Move the leader slowly first. Stop with Ctrl-C.

    CHECKThe follower tracks the leader joint by joint in the same direction, the gripper closes when the trigger is pulled, and no joint overshoots or oscillates at rest.

    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

    —

    Tools

    —

    Torque

    —

    Time

    —

    After

    12, 13

    Source

    huggingface.co

15. Policy
    15

    Record a dataset

    Add a camera and record with `lerobot-record --robot.type=koch_follower ... --robot.cameras="{ front: {type: opencv, index_or_path: 0, width: 1920, height: 1080, fps: 30}}" --teleop.type=koch_leader ... --dataset.repo_id=${HF_USER}/record-test --dataset.num_episodes=5 --dataset.single_task="Grab the block"`. The docs suggest at least 50 episodes (10 per location) for a first task. A camera is not part of the Koch BOM.

    CHECKThe dataset appears on the Hub (or locally) with the expected number of episodes and plays back in the dataset visualizer with camera frames and joint states in sync.

    Parts in

    • HuggingFace_Block (optional 2x4-Lego-size test object)printed.extras.huggingface-block
    • LeRobot_Block (optional 2x4-Lego-size test object)printed.extras.lerobot-block

    Tools

    —

    Torque

    —

    Time

    —

    After

    14

    Source

    huggingface.co

16. 16

    Train an ACT policy on the recorded data

    Run `lerobot-train --dataset.repo_id=${HF_USER}/<dataset> --policy.type=act --output_dir=outputs/train/act_koch --job_name=act_koch --policy.device=cuda --policy.repo_id=${HF_USER}/my_policy`, then evaluate on the arm by recording with `--policy.path` set to the checkpoint.

    CHECKTraining loss decreases and checkpoints are written under `outputs/train/act_koch/checkpoints/`; the policy repeats the task on the real arm in several evaluation episodes.

    Parts in

    —

    Tools

    NVIDIA GPU or Apple silicon

    Torque

    —

    Time

    —

    After

    15

    Source

    huggingface.co

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