Build HopeJR

Steps

14

Subassemblies

7

Hands-on time (sum)

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Critical path

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Your progress · this device

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

1. Fabrication
   01

   Print the arm and hand

   Print the four right-side arm files and the spool cover from Arm/3dprint files/arm (left_* files for a left arm). The upstream gives no material, layer or infill settings. Arm/STEP/arm.step and hand.step are the reference geometry. Tolerances were relaxed in the 2025 revision and threaded inserts were replaced by through-bolts.

   CHECKA 20 x 27 x 4 mm bearing and a Feetech STS servo each drop into their printed pockets by hand with no visible play.

   Parts in

   • Right shoulder (right_shoulder.stl; left_shoulder.stl for a left arm)printed.shoulder
   • Right humeral / upper arm (right_humeral.stl)printed.humeral
   • Right forearm (right_forearm.stl)printed.forearm
   • Right hand, palm + fingers (right_hand.stl, multi-body file)printed.hand
   • Tendon spool cover (spoolcover.stl; copies needed not stated)printed.spoolcover

   Tools

   FDM printer

   Torque

   —

   Time

   —

   After

   Start

   Source

   github.com

2. 02

   Print the exoskeleton and glove

   Print right_exo.stl and right_glove.stl from Arm/3dprint files/exoskeleton. Geometry reference: Arm/STEP/exoskeleton.step and glove.step.

   CHECKA 3 x 2 mm magnet and a 6 x 10 x 3 mm bearing seat in their printed pockets on the exoskeleton, and the glove fits the operator's hand.

   Parts in

   • Right teleop exoskeleton (right_exo.stl)printed.exo
   • Right teleop glove (right_glove.stl)printed.glove

   Tools

   FDM printer

   Torque

   —

   Time

   —

   After

   Start

   Source

   github.com

3. 03

   Order the assembled PCBs from JLCPCB

   For each folder in Arm/PCB, upload gerber.zip to JLCPCB, select PCB assembly, then upload that folder's BOM and POS (CPL) files. The Homunculus board carries the ESP32-C3, 16-channel mux and op-amp buffers for the Hall sensors; the connector boards join servo/sensor cables so no soldering is needed.

   CHECKJLCPCB's placement preview shows every BOM designator placed (e.g. U1-U6 on the Homunculus board), and a delivered Homunculus board enumerates as a USB serial device when plugged in over USB-C.

   Parts in

   • Homunculus sensor PCB, JLCPCB-assembled (ESP32-C3-WROOM-02, CD74HC4067 16-ch mux, 3x OPA340UA, AMS1117-3.3, USB-C, 16x JST-SH 3-pin)electronics.pcb-homunculus
   • 12-connector breakout PCB (12x JST EH B3B 2.50 mm vertical)electronics.pcb-12-connector
   • 7-connector breakout PCB (7x JST, LCSC C722693)electronics.pcb-7-connector

   Tools

   —

   Torque

   —

   Time

   —

   After

   Start

   Source

   github.com

4. Hand
   04

   Hand: finger servos, tendons, springs

   No step-by-step guide is published; work from hand.step. Per the Arm README: each finger has three SCS0009 servos (radial flexor, ulnar flexor, PIP/DIP) and the thumb four (CMC, MCP, PIP, DIP), the DIP joint is underactuated, tendons are locked with screws rather than crimps, run through PTFE tubes, and wind on spools that linearise finger motion against servo angle. Assign servo IDs 1-16 in the order LeRobot's hope_jr_hand.py expects (thumb_cmc=1 ... pinky_pip_dip=16).

   CHECKWith tendons tensioned, turning each servo horn by hand flexes the matching finger and the springs return it to open; all 16 servos answer on the bus with IDs 1-16.

   Parts in

   • Right hand, palm + fingers (right_hand.stl, multi-body file)printed.hand
   • Tendon spool cover (spoolcover.stl; copies needed not stated)printed.spoolcover
   • Feetech SCS0009 micro serial servo, hand (3 per finger x4 + 4 thumb)actuator.scs0009
   • Braided fishing line 0.33 mm, 63 lb test (finger tendons)other.tendon-line
   • PTFE tube (3D-printer filament type) for tendon sheathsother.ptfe-tube
   • Tension spring 15 mm long, 0.3 mm wire, 3 mm OD (set of 10; thumb + fingers)other.spring-15mm
   • Tension spring 20 mm long, 0.3 mm wire, 3 mm OD (sets of 10; fingers)other.spring-20mm
   • Finger protectors (fingertip covers)other.finger-protectors
   • M2 screw assortment set (hand)fastener.m2-set
   • Ball bearing 20 x 27 x 4 mm (arm)structure.bearing-20x27x4

   Tools

   —

   Torque

   —

   Time

   —

   After

   01

   Source

   github.com

5. Arm
   05

   Arm: shoulder, humeral, elbow, forearm, wrist

   No step-by-step guide is published; work from arm.step and the BOM's placement notes (M4x65: 2 upper shoulder, 2 armpit, 2 wrist; M4x50/45/35 and one M4x30: humeral; two M4x30: lower shoulder; M4x25: upper elbow; M6x35 with spacers: 2 elbow, 2 shoulder; 70x90x10 bearing at the wrist, 50x65x7 at the shoulder). Servo IDs per LeRobot hope_jr_arm.py: shoulder_pitch=1 (SM8512BL), shoulder_yaw=2, shoulder_roll=3, elbow_flex=4, wrist_roll=5, wrist_yaw=6, wrist_pitch=7. Route wires behind the mantle.

   CHECKUnpowered, every arm joint turns through its range by hand with no binding, and all 7 servos answer on the URT-1 bus at their IDs 1-7.

   Parts in

   • Right shoulder (right_shoulder.stl; left_shoulder.stl for a left arm)printed.shoulder
   • Right humeral / upper arm (right_humeral.stl)printed.humeral
   • Right forearm (right_forearm.stl)printed.forearm
   • Feetech SM8512BL 12 V 85 kg high-torque servo, shoulder pitchactuator.sm8512bl
   • Feetech STS3250 50 kg.cm serial bus servo, shoulder yaw + elbow flexactuator.sts3250
   • Feetech STS3215 12 V 30 kg.cm serial bus servo, armactuator.sts3215-12v
   • Ball bearing 70 x 90 x 10 mm (wrist)structure.bearing-70x90x10
   • Ball bearing 50 x 65 x 7 mm (shoulder)structure.bearing-50x65x7
   • Ball bearing 20 x 27 x 4 mm (arm)structure.bearing-20x27x4
   • M4 screws: 6x 65 mm, 1x 50 mm, 1x 45 mm, 1x 35 mm, 3x 30 mm, 1x 25 mm (shoulder, armpit, wrist, humeral, elbow)fastener.m4-screws
   • M4 nut assortment set (arm)fastener.m4-nuts
   • M6 x 35 mm screw (2x elbow, 2x shoulder)fastener.m6x35
   • M6 spacer set (2x elbow, 2x shoulder)fastener.m6-spacers

   Tools

   —

   Torque

   —

   Time

   —

   After

   01

   Source

   github.com

6. Teleop
   06

   Exoskeleton: Hall encoders, bearings, straps

   No step-by-step guide is published; work from exoskeleton.step. Each exo joint mirrors a robot joint; each joint gets one diametric magnet, upper-arm joints use two SS49E sensors (sin/cos pair). Plug sensors into the Homunculus PCB with the JST cables, and strap the exo to forearm, shoulder and torso with the velcro straps.

   CHECKFlashed with exo.cs, the serial monitor at 115200 baud prints 16 raw values plus 5 angles (0-3600), and rotating each instrumented joint changes only its own angle smoothly with no wrap mid-range.

   Parts in

   • Right teleop exoskeleton (right_exo.stl)printed.exo
   • Ball bearing 6 x 10 x 3 mm (exoskeleton upper-arm joints)structure.bearing-6x10x3
   • Diametrically magnetised N38 neodymium disc magnet, 3 mm x 2 mm (one per joint)sensor.magnet-3x2
   • SS49E linear Hall sensor (1 per hand/wrist joint, 2 per upper-arm joint)sensor.ss49e
   • Homunculus sensor PCB, JLCPCB-assembled (ESP32-C3-WROOM-02, CD74HC4067 16-ch mux, 3x OPA340UA, AMS1117-3.3, USB-C, 16x JST-SH 3-pin)electronics.pcb-homunculus
   • JST-SH 3-pin pre-crimped cables, sets of 10: 1x 10 cm, 1x 15 cm, 2x 20 cm, 1x 30 cm (same-direction for 15-30 cm)cable.jst-3pin
   • M3 screw assortment set (exoskeleton + glove)fastener.m3-set
   • Velcro strap 20 mm wide: 2x forearm, 2x shoulder, 2x half-torso lengthother.velcro-strap

   Tools

   —

   Torque

   —

   Time

   —

   After

   02, 03

   Source

   github.com

7. 07

   Glove: finger Hall sensors

   No step-by-step guide is published; work from glove.step and Project Homunculus (the glove's origin). One magnet + one SS49E per hand joint, wired to the second Homunculus PCB.

   CHECKFlashed with glove.cs, the serial stream at 115200 baud shows 16 raw readings and flexing each finger moves only its own channels.

   Parts in

   • Right teleop glove (right_glove.stl)printed.glove
   • Diametrically magnetised N38 neodymium disc magnet, 3 mm x 2 mm (one per joint)sensor.magnet-3x2
   • SS49E linear Hall sensor (1 per hand/wrist joint, 2 per upper-arm joint)sensor.ss49e
   • Homunculus sensor PCB, JLCPCB-assembled (ESP32-C3-WROOM-02, CD74HC4067 16-ch mux, 3x OPA340UA, AMS1117-3.3, USB-C, 16x JST-SH 3-pin)electronics.pcb-homunculus
   • JST-SH 3-pin pre-crimped cables, sets of 10: 1x 10 cm, 1x 15 cm, 2x 20 cm, 1x 30 cm (same-direction for 15-30 cm)cable.jst-3pin
   • M3 screw assortment set (exoskeleton + glove)fastener.m3-set

   Tools

   —

   Torque

   —

   Time

   —

   After

   02, 03

   Source

   github.com

8. Arm
   08

   Mount the hand on the wrist

   Join the hand to the wrist bearing and route the hand servo bus back along the arm to the Waveshare driver.

   CHECKWrist roll, yaw and pitch still move freely by hand with the hand attached, and no cable pulls tight at any wrist extreme.

   Parts in

   • Right hand, palm + fingers (right_hand.stl, multi-body file)printed.hand
   • Right forearm (right_forearm.stl)printed.forearm

   Tools

   —

   Torque

   —

   Time

   —

   After

   04, 05

   Source

   github.com

9. Bring-up
   09

   Flash the ESP32-C3 teleop firmware

   Arm/code/exo.cs and glove.cs are Arduino sketches (despite the .cs extension): rename to .ino, build for ESP32-C3 and upload to the exo and glove boards respectively. Both read a 16-channel mux on S0-S3 = GPIO 5, 6, 8, 7 and analog input GPIO 4, and stream at 115200 baud, matching LeRobot's homunculus baud_rate default.

   CHECK`lerobot-find-port` lists both teleop boards, and each streams one line of space-separated integers per scan.

   Parts in

   • Homunculus sensor PCB, JLCPCB-assembled (ESP32-C3-WROOM-02, CD74HC4067 16-ch mux, 3x OPA340UA, AMS1117-3.3, USB-C, 16x JST-SH 3-pin)electronics.pcb-homunculus
   • USB-C to USB-A cable, 3 m (arm + hand)cable.usb-c-a-3m

   Tools

   Arduino IDE (or arduino-cli) with ESP32 core

   Torque

   —

   Time

   —

   After

   06, 07

   Source

   github.com

10. Electrical
    10

    Wire servo buses and power

    Safety · human-verified required

    Arm bus: 12 V 5 A supply into the URT-1 board. Hand bus: 5 V 4 A supply into the Waveshare driver (SCS0009 are low-voltage servos, never put them on 12 V). Connect each board to the host with a 3 m USB-C cable. Use the connector PCBs to join servo leads without soldering.

    CHECKBefore plugging servos in, a multimeter reads about 12 V on the arm bus and about 5 V on the hand bus with correct polarity; with servos connected, `lerobot-find-port` shows both adapters.

    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 URT-1 serial bus adapter board (arm bus)electronics.urt-1
    • Waveshare serial bus servo driver board (hand bus)electronics.waveshare-servo-driver
    • Power supply 12 V 5 A + DC adapter (arm)power.psu-12v-5a
    • Power supply 5 V 4 A (hand)power.psu-5v-4a
    • USB-C to USB-A cable, 3 m (arm + hand)cable.usb-c-a-3m
    • 12-connector breakout PCB (12x JST EH B3B 2.50 mm vertical)electronics.pcb-12-connector
    • 7-connector breakout PCB (7x JST, LCSC C722693)electronics.pcb-7-connector

    Tools

    —

    Torque

    —

    Time

    —

    After

    08

    Source

    github.com

11. Bring-up
    11

    Install LeRobot with HopeJR extras

    Clone huggingface/lerobot and `pip install -e ".[hopejr]"` (pulls the Feetech SDK and pygame for the calibration GUI). Run `lerobot-find-port` and note the ports for arm, hand, exoskeleton and glove.

    CHECK`python -c "import lerobot.robots.hope_jr"` succeeds and four distinct serial ports are identified.

    Parts in

    —

    Tools

    Host computer (Linux/macOS), Python

    Torque

    —

    Time

    —

    After

    10, 09

    Source

    huggingface.co

12. 12

    Calibrate hand, arm, glove and exoskeleton

    Safety · human-verified required

    `lerobot-calibrate --robot.type=hope_jr_hand --robot.side=right ...` and `--robot.type=hope_jr_arm ...` open a range-finder GUI: set min/max per joint and Save (writes limits to the motors). Keep ulnar and radial flexor ranges the same size. Then `--teleop.type=homunculus_glove` and `--teleop.type=homunculus_arm`: move every joint through its full range and press ENTER. Files land in ~/.cache/huggingface/lerobot/calibration.

    CHECKFour calibration JSON files exist under ~/.cache/huggingface/lerobot/calibration, and each teleop joint's recorded MIN < MAX.

    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 SCS0009 micro serial servo, hand (3 per finger x4 + 4 thumb)actuator.scs0009
    • Feetech STS3250 50 kg.cm serial bus servo, shoulder yaw + elbow flexactuator.sts3250
    • Feetech STS3215 12 V 30 kg.cm serial bus servo, armactuator.sts3215-12v
    • Feetech SM8512BL 12 V 85 kg high-torque servo, shoulder pitchactuator.sm8512bl

    Tools

    —

    Torque

    —

    Time

    —

    After

    11

    Source

    huggingface.co

13. 13

    First motion: teleoperate hand and arm

    Safety · human-verified required

    Run `lerobot-teleoperate` for the hand (hope_jr_hand + homunculus_glove) and, in a separate shell, for the arm (hope_jr_arm + homunculus_arm); the docs say both cannot share a process due to Feetech middleware globals. Start at --fps=30. hope_jr_arm supports max_relative_target to clamp step size; set it for the first run and keep the arm clear of people.

    CHECKClosing the glove hand closes the robot hand, and moving each exo joint moves the matching robot joint in the same direction, with --display_data=true showing matching values.

    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

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    Tools

    —

    Torque

    —

    Time

    —

    After

    12

    Source

    huggingface.co

14. Policy
    14

    Record, train and evaluate an ACT policy (experimental)

    `lerobot-record` with a camera and the glove to capture episodes, `lerobot-train --policy.type=act` on the dataset, then `lerobot-record --policy.path=...` to evaluate. The docs mark record/replay/train for HopeJR as experimental and only show the hand.

    CHECKA recorded episode replays with `lerobot-replay` and the robot hand repeats the demonstrated motion.

    Parts in

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    Tools

    USB camera (OpenCV)

    Torque

    —

    Time

    —

    After

    13

    Source

    huggingface.co

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