Build ToddlerBot

Steps

16

Subassemblies

10

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

   Order the 8-channel TTL power board (PCBA) first

   The docs say to order the PCB before anything else (about 10 days lead time). Upload TTLPowerBoardV8.zip to JLCPCB, choose Standard PCBA with both sides assembled, then upload bom_v8.csv and positions_v8.csv. If a part is out of stock, use the documented substitutes: C160259 (JST EH), C2902689 (2x06 pin socket), C5188440 (5 mm terminal block).

   CHECKIn the JLCPCB parts-confirmation screen every BOM row is ticked and the front/back placement previews match the v8placementF/B images in the docs.

   Parts in

   • TTL power/communication board V8 (8-channel, CH348L USB-to-TTL, 3x XT30 out, 2 buck headers), JLCPCB PCBAelectronics.pcb-8ch

   Tools

   —

   Torque

   —

   Time

   —

   After

   Start

   Source

   hshi74.github.io

2. 02

   Print the robot and calibration plates

   Bambu users can print straight from the MakerWorld 2XC release. Other printers: download the 3MF files and keep the published part orientations and profile, which the docs say matter for strength. Remove supports before assembly. For custom edits, use the Onshape document.

   CHECKAll 13 plates listed here are printed with supports removed. The per-plate filament use roughly matches MakerWorld (about 1.05 kg PLA-CF and 0.47 kg PLA across these 13 plates).

   Parts in

   • Arm plate 1 (arms are identical left/right) (MakerWorld 2XC profile, plate 1)printed.arm-1
   • Arm plate 2 (MakerWorld 2XC profile, plate 2)printed.arm-2
   • Left leg plate (MakerWorld 2XC profile, plate 3)printed.leg-left
   • Right leg plate (MakerWorld 2XC profile, plate 4)printed.leg-right
   • Torso plate (MakerWorld 2XC profile, plate 5)printed.torso
   • Torso + head + neck small parts (MakerWorld 2XC profile, plate 10)printed.torso-head-neck
   • Head cover (MakerWorld 2XC profile, plate 11)printed.head-cover
   • Waist (gears: tips page recommends PLA-CF with more wall loops) (MakerWorld 2XC profile, plate 13)printed.waist
   • Feet, rubber-pad version (alt: plate 15 'Foot without Rubber', 34 g, 1.1 h) (MakerWorld 2XC profile, plate 17)printed.foot
   • Palms, rubber-pad version (alt: plate 16 'Palm with TPU', 62 g TPU, 5.1 h) (MakerWorld 2XC profile, plate 18)printed.palm
   • Unlabelled plate (contents not named on MakerWorld) (MakerWorld 2XC profile, plate 19)printed.plate-19
   • Zero-point calibration devices, set 1 (tooling) (MakerWorld 2XC profile, plate 8)printed.calibrator-1
   • Zero-point calibration devices, set 2 (tooling) (MakerWorld 2XC profile, plate 12)printed.calibrator-2
   • Bambu PLA-CF filament, 1 kg (structural parts)printed.filament-pla-cf
   • Bambu PLA Basic filament, 1 kg (calibration devices, stand)printed.filament-pla

   Tools

   Bambu Lab printer (recommended; sheet lists X1-Carbon Combo + smooth PEI plate + glue)

   Torque

   —

   Time

   —

   After

   Start

   Source

   hshi74.github.io

3. 03

   Sort and count the hardware

   The manual preface: sort and count every hardware piece into separate compartments so leftovers reveal skipped steps. Use the pre-coated M2x6 screws, or threadlocker on the screws highlighted yellow in the manual. If a joint feels stuck, check screw length first.

   CHECKCounted piles match the sheet's Screws tab (e.g. M2x6 106, M2x8 43, M2.5x4 32, M3x10 studs 25, bearings 683 x12, 684 x14, AXK0414 x18).

   Parts in

   • M2x6 pre-coated (thread-locking) screws, 200 pcs (Screws tab: 106 used)fastener.m2x6-precoated
   • M2 button-head screw/nut/washer kit, 660 pcs (Screws tab: M2x4 24, M2x8 43, M2x10 20)fastener.m2-kit
   • M2.5 button-head screw kit, 705 pcs (Screws tab: M2.5x4 32, x6 8, x10 19)fastener.m2_5-kit
   • M3 countersunk screw kit, 565 pcs (Screws tab: M3x4 5, x6 14, x8 4, x10 11, x14 1; flat head x6 2, x8 5, x12 6)fastener.m3-flat-kit
   • M3x8 set screws / studs, 50 pcs (Screws tab: 8 used)fastener.m3x8-set
   • M3x10 set screws / studs, 50 pcs (Screws tab: 25 used)fastener.m3x10-set
   • M4 button-head screw kit, 675 pcs (Screws tab: M4x8 5, x12 1, x20 6, x25 2, x30 2)fastener.m4-kit
   • M4 x 40-60 mm socket head screws, 50 pcs (Screws tab: M4x55 1, waist)fastener.m4-long-kit
   • M3 + M4 stainless lock nut kit, 182 pcsfastener.locknuts
   • 683-2RS ball bearing 3x7x3 mm (10-pack)structure.bearing-683
   • 684ZZ ball bearing 4x9x4 mm (10-pack)structure.bearing-684
   • AXK0414 thrust needle roller bearing + 2 washersstructure.bearing-axk0414
   • Oilless sleeve bushing 3 mm bore x 5 mm OD x 5 mm (10-pack)structure.bushing-3x5x5

   Tools

   —

   Torque

   —

   Time

   —

   After

   Start

   Source

   docs.google.com

4. Arms
   04

   Arms (x2, identical)

   The arms go first because they are the easiest. Per the manual, each arm takes 3x 2XL430, 1x XC430 and 3x HN11-I101 idler sets. Plug the cable in on the idler side first, and seat studs flush with or slightly below the surface. Left and right arms are identical. The 2.0 assembly video walks through the arm.

   CHECKEach arm joint turns by hand through its range with no binding, and all studs sit flush or below the surface.

   Parts in

   • DYNAMIXEL 2XL430-W250-T (dual-axis, arms: 3 per arm)actuator.2xl430-w250
   • DYNAMIXEL XC430-T240BB-Tactuator.xc430-t240bb
   • DYNAMIXEL HN11-I101 idler setstructure.idler-hn11
   • AXK0414 thrust needle roller bearing + 2 washersstructure.bearing-axk0414
   • 684ZZ ball bearing 4x9x4 mm (10-pack)structure.bearing-684
   • M2 button-head screw/nut/washer kit, 660 pcs (Screws tab: M2x4 24, M2x8 43, M2x10 20)fastener.m2-kit
   • M2.5 button-head screw kit, 705 pcs (Screws tab: M2.5x4 32, x6 8, x10 19)fastener.m2_5-kit
   • M3x8 set screws / studs, 50 pcs (Screws tab: 8 used)fastener.m3x8-set
   • M3x10 set screws / studs, 50 pcs (Screws tab: 25 used)fastener.m3x10-set
   • M4 button-head screw kit, 675 pcs (Screws tab: M4x8 5, x12 1, x20 6, x25 2, x30 2)fastener.m4-kit
   • Arm plate 1 (arms are identical left/right) (MakerWorld 2XC profile, plate 1)printed.arm-1
   • Arm plate 2 (MakerWorld 2XC profile, plate 2)printed.arm-2
   • Palms, rubber-pad version (alt: plate 16 'Palm with TPU', 62 g TPU, 5.1 h) (MakerWorld 2XC profile, plate 18)printed.palm
   • Vibra-TITE 213 VC-3 threadlocker, 5 mL (about 100 screws need it per the manual)other.threadlocker

   Tools

   Electric screwdriver (low torque for M2), PH1 screwdriver, Allen keys

   Torque

   —

   Time

   —

   After

   02, 03

   Source

   hshi74.github.io

5. Legs
   05

   Legs (left, then mirrored right)

   Per the manual, each leg takes 2x XM430, 1x XC430, 1x 2XC430, 1x XC330, 2x HN11 and 1x HN12. On the left hip roll the 2XC430 actuation side faces backward; on the right it faces forward. Watch the XC330 orientation. The right leg mirrors the left. 2.0 legs are 30 mm shorter and drop the knee parallel links.

   CHECKMotor orientations on both legs match the L/R orientation figure in the manual, and each leg joint moves by hand without cable snag.

   Parts in

   • DYNAMIXEL XM430-W210-T (legs: 2 per leg)actuator.xm430-w210
   • DYNAMIXEL 2XC430-W250-T (dual-axis, hip)actuator.2xc430-w250
   • DYNAMIXEL XC430-T240BB-Tactuator.xc430-t240bb
   • DYNAMIXEL XC330-T288-T (neck, waist, ankle, torso)actuator.xc330-t288
   • DYNAMIXEL HN11-I101 idler setstructure.idler-hn11
   • DYNAMIXEL HN12-I101 idler setstructure.idler-hn12
   • AXK0414 thrust needle roller bearing + 2 washersstructure.bearing-axk0414
   • 683-2RS ball bearing 3x7x3 mm (10-pack)structure.bearing-683
   • 684ZZ ball bearing 4x9x4 mm (10-pack)structure.bearing-684
   • M2 button-head screw/nut/washer kit, 660 pcs (Screws tab: M2x4 24, M2x8 43, M2x10 20)fastener.m2-kit
   • M2.5 button-head screw kit, 705 pcs (Screws tab: M2.5x4 32, x6 8, x10 19)fastener.m2_5-kit
   • M3 countersunk screw kit, 565 pcs (Screws tab: M3x4 5, x6 14, x8 4, x10 11, x14 1; flat head x6 2, x8 5, x12 6)fastener.m3-flat-kit
   • M4 button-head screw kit, 675 pcs (Screws tab: M4x8 5, x12 1, x20 6, x25 2, x30 2)fastener.m4-kit
   • M3 + M4 stainless lock nut kit, 182 pcsfastener.locknuts
   • Left leg plate (MakerWorld 2XC profile, plate 3)printed.leg-left
   • Right leg plate (MakerWorld 2XC profile, plate 4)printed.leg-right
   • Feet, rubber-pad version (alt: plate 15 'Foot without Rubber', 34 g, 1.1 h) (MakerWorld 2XC profile, plate 17)printed.foot
   • 5 mm rubber tape (foot / palm grip)other.rubber-tape

   Tools

   Allen keys, Wrench or pliers

   Torque

   —

   Time

   —

   After

   02, 03

   Source

   hshi74.github.io

6. Head
   06

   Head: eyes, speaker, neck motor

   Mount both fisheye cameras (with cables) and the speaker driver with double-sided tape. Plug the cable in before closing the shell; the micro-USB port on the driver board is fragile. Plug in the neck motor cable on both sides. See the camera-cable, speaker-cable and head videos.

   CHECKBoth camera cables and the speaker cable exit the head, and the neck XC330 has cables on both sides.

   Parts in

   • Arducam 1080P IMX291 160° fisheye USB camera with mic (eyes)sensor.fisheye-camera
   • Phone loudspeaker (iPhone SE 2020/2022 replacement part)electronics.speaker
   • HiLetgo M38 Bluetooth MP3 audio receiver board (3-pack), speaker driverelectronics.speaker-driver
   • USB-A to micro-USB cable, 1.5 ft (speaker)cable.usb-micro-1.5ft
   • DYNAMIXEL XC330-T288-T (neck, waist, ankle, torso)actuator.xc330-t288
   • 683-2RS ball bearing 3x7x3 mm (10-pack)structure.bearing-683
   • 684ZZ ball bearing 4x9x4 mm (10-pack)structure.bearing-684
   • Head cover (MakerWorld 2XC profile, plate 11)printed.head-cover
   • Torso + head + neck small parts (MakerWorld 2XC profile, plate 10)printed.torso-head-neck

   Tools

   —

   Torque

   —

   Time

   —

   After

   02

   Source

   hshi74.github.io

7. Waist
   07

   Waist (joins both legs)

   Per the manual: 2x XC330 and 2x HN11 idler sets, plus the M4x55 bolt. Match the motor orientation figure. The waist link flexes to let the motors in. The manual notes the waist link geometry changed after it was drawn, but the steps are the same.

   CHECKBoth legs hang from the waist, the waist turns by hand in roll and yaw, and the M4x55 screw is tight.

   Parts in

   • DYNAMIXEL XC330-T288-T (neck, waist, ankle, torso)actuator.xc330-t288
   • DYNAMIXEL HN11-I101 idler setstructure.idler-hn11
   • AXK0414 thrust needle roller bearing + 2 washersstructure.bearing-axk0414
   • 684ZZ ball bearing 4x9x4 mm (10-pack)structure.bearing-684
   • M4 x 40-60 mm socket head screws, 50 pcs (Screws tab: M4x55 1, waist)fastener.m4-long-kit
   • Waist (gears: tips page recommends PLA-CF with more wall loops) (MakerWorld 2XC profile, plate 13)printed.waist

   Tools

   Allen key

   Torque

   —

   Time

   —

   After

   05

   Source

   hshi74.github.io

8. Torso
   08

   Torso shell, neck, IMU (manual torso steps 1-8)

   Build the torso up to step 8 of the manual. Plug in the IMU cable (4 jumper wires taped together, pin map in the manual) before closing that section. The manual singles out one step-3 screw as possibly the most critical in the build; tighten it fully.

   CHECKThe IMU is wired per the manual's pin map, the arms and head are attached, and the neck rotates by hand.

   Parts in

   • Torso plate (MakerWorld 2XC profile, plate 5)printed.torso
   • Torso + head + neck small parts (MakerWorld 2XC profile, plate 10)printed.torso-head-neck
   • DYNAMIXEL XC330-T288-T (neck, waist, ankle, torso)actuator.xc330-t288
   • Adafruit BNO085 9-DOF IMU breakout (STEMMA QT)sensor.imu-bno085
   • Jumper wire assortment (IMU to Jetson header)cable.jumper-wire
   • M3 countersunk screw kit, 565 pcs (Screws tab: M3x4 5, x6 14, x8 4, x10 11, x14 1; flat head x6 2, x8 5, x12 6)fastener.m3-flat-kit
   • M2.5 button-head screw kit, 705 pcs (Screws tab: M2.5x4 32, x6 8, x10 19)fastener.m2_5-kit
   • AXK0414 thrust needle roller bearing + 2 washersstructure.bearing-axk0414

   Tools

   —

   Torque

   —

   Time

   —

   After

   04, 06, 07

   Source

   hshi74.github.io

9. Bring-up
   09

   Set Dynamixel IDs and baud rate

   Set IDs one motor at a time to avoid conflicts, using the ID list in the manual's wiring figure. Set every motor to 2 Mbps: the tips page says XC330 cannot sustain 4 Mbps. Each 2X motor shows two IDs; move the joint to see which one changes. The 'ID the Motors' video walks through it. The repo has no ID-assignment script.

   CHECKA Dynamixel Wizard scan at 2 Mbps finds every motor at its assigned ID with no duplicates.

   Parts in

   • DYNAMIXEL 2XC430-W250-T (dual-axis, hip)actuator.2xc430-w250
   • DYNAMIXEL 2XL430-W250-T (dual-axis, arms: 3 per arm)actuator.2xl430-w250
   • DYNAMIXEL XC330-T288-T (neck, waist, ankle, torso)actuator.xc330-t288
   • DYNAMIXEL XC430-T240BB-Tactuator.xc430-t240bb
   • DYNAMIXEL XM430-W210-T (legs: 2 per leg)actuator.xm430-w210

   Tools

   Dynamixel Wizard 2.0, U2D2 + U2D2 power hub + 12 V adapter (per the manual; the sheet lists U2D2/hub only under Teleoperation)

   Torque

   —

   Time

   —

   After

   08

   Source

   github.com

10. Compute
    10

    Set up the Jetson Orin NX before installing it

    Flash JetPack 6.1+ (the Seeed reComputer J4012 guide), fit the M.2 Wi-Fi card, set power mode 0:MAXN, install the real-time kernel, then create the conda env and run `pip install -e ".[jetson]"`. The USB-C port is for flashing only.

    CHECK`uname -r` ends in `-rt-tegra`, the Jetson joins Wi-Fi and accepts SSH, and `pytest tests/` runs in the toddlerbot env.

    Parts in

    • NVIDIA Jetson Orin NX 16GB (Seeed reComputer J4012)compute.jetson-orin-nx
    • AW-CB375NF M.2 (A/E key) Wi-Fi 5 + BLE cardelectronics.wifi-card
    • Wi-Fi 6E internal antenna pair, IPX MHF4electronics.wifi-antenna

    Tools

    Host PC for flashing, HDMI, keyboard, mouse

    Torque

    —

    Time

    —

    After

    08

    Source

    hshi74.github.io

11. Electrical
    11

    Power board and motor-chain wiring

    Safety · human-verified required

    Prepare the power board as in the Power Board video: two D36V50F12 bucks on the back headers, switch on the terminal block, XT30 to the Jetson via the barrel jack. Chain the motors to the board roots as the manual's diagram shows, using longer JST EH leads for the long runs. Keep the manual's slot allocation so current is balanced across the bucks. Connect the USB hub (cameras, speaker) and the board to the Jetson.

    CHECKBefore any motor is connected, the Jetson XT30 output reads 12 V with correct polarity. With the chains connected, every motor ID appears in a scan from the Jetson.

    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

    • TTL power/communication board V8 (8-channel, CH348L USB-to-TTL, 3x XT30 out, 2 buck headers), JLCPCB PCBAelectronics.pcb-8ch
    • Pololu D36V50F12 12 V 4.5 A step-down regulatorpower.buck-12v
    • JST EH pre-crimped cable (long motor-chain runs)cable.jst-eh-precrimped
    • JST EH 3-pin housingcable.jst-eh-housing
    • XT30 male + female plugs (5 pairs)cable.xt30-pairs
    • XT30 to XT60 adapter leads (4-pack)cable.xt30-xt60
    • Barrel jack connector 5.5x2.5 mm (DC5525), Jetson powercable.barrel-jack
    • USB-A to micro-USB cable, 0.5 ftcable.usb-micro-0.5ft
    • USB hub port splitter (cameras + speaker)electronics.usb-hub
    • Rocker switch (5-pack)power.rocker-switch

    Tools

    Soldering station, Wire stripper, Heat-shrink

    Torque

    —

    Time

    —

    After

    09, 01

    Source

    hshi74.github.io

12. 12

    Battery, tester and first power-on

    Safety · human-verified required

    Bring the robot up first on the bench supply over the 14 AWG tether; tape the supply's voltage and current buttons, per the tips page. Then fit the LiPo with the voltage tester attached to prevent over-discharge. The battery box goes into the torso in one pose; if the front cover will not close, fix the box pose and wire routing. An optional DIY 21700 pack is documented separately.

    CHECKOn battery, the tester shows every cell above its alarm threshold, the Jetson boots, and all motors respond. The front cover knobs close without force.

    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

    • 2000 mAh LiPo batterypower.battery-lipo
    • LiPo battery voltage tester / low-voltage alarmpower.lipo-tester
    • LiPo balance chargerpower.lipo-charger
    • 14 AWG 2-conductor power cable (bench-supply tether)cable.wire-14awg

    Tools

    30 V 10 A bench supply (sheet Tools section)

    Torque

    —

    Time

    —

    After

    11

    Source

    hshi74.github.io

13. Bring-up
    13

    Zero-point calibration with printed jigs

    Safety · human-verified required

    Insert the calibration devices until they click and lock the joints; route cables clear of them. The knee lower limit is its own zero reference. Run `python toddlerbot/tools/calibrate_zero.py --robot toddlerbot_2xc` (optionally with `--parts ...`). Check config_motors.json, then run `python toddlerbot/descriptions/add_configs.py --robot toddlerbot_2xc`.

    CHECKWith the jigs in, no calibrated joint can be moved by hand, and after add_configs the zero offsets in config_motors.json have been propagated to the robot config.

    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

    • Zero-point calibration devices, set 1 (tooling) (MakerWorld 2XC profile, plate 8)printed.calibrator-1
    • Zero-point calibration devices, set 2 (tooling) (MakerWorld 2XC profile, plate 12)printed.calibrator-2

    Tools

    —

    Torque

    —

    Time

    —

    After

    12, 10

    Source

    hshi74.github.io

14. 14

    Standing test

    Safety · human-verified required

    Run `python toddlerbot/policies/run_policy.py --policy stand --robot toddlerbot_2xc --sim real`. Hold the robot whenever you stop a script or cut power: the motors disable and it will fall. Also hold it in the air with stand running and feel for backlash, which usually means loose screws.

    CHECKToddy stands upright and steady on flat ground under the stand policy, with no joint showing more backlash than the XC330 joints.

    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

    13

    Source

    hshi74.github.io

15. 15

    IMU-feedback zero fine-tuning

    Safety · human-verified required

    If the robot leans after jig calibration (joint backlash), run `python toddlerbot/policies/run_policy.py --policy calibrate --robot toddlerbot_2xc --sim real`. It runs PID on torso pitch from the IMU. Press Ctrl+C once it is upright, holding the robot; the zero point is saved.

    CHECKRerunning the stand policy after fine-tuning, the torso stays visibly upright with no forward or backward lean.

    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

    • Adafruit BNO085 9-DOF IMU breakout (STEMMA QT)sensor.imu-bno085

    Tools

    —

    Torque

    —

    Time

    —

    After

    14

    Source

    hshi74.github.io

16. Software
    16

    Keyframe replay in sim, then published RL checkpoints

    Safety · human-verified required

    Check the install in MuJoCo with `python toddlerbot/policies/run_policy.py --policy replay --path motion/push_up_2xc.lz4 --vis view`. Download a 2XC checkpoint (e.g. toddlerbot_2xc_walk_rsl_20251226_114612) from the Google Drive folder linked in the README, try it in sim, then on the real robot with a spotter. To train your own: `python toddlerbot/locomotion/train_mjx.py --gin-file walk --env walk`.

    CHECKThe push-up replay plays in the MuJoCo viewer without errors, and the walk checkpoint walks in simulation before any real-robot run.

    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

    15

    Source

    github.com

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