Open Duck Mini v2 parts list
A 42 cm 3D printed biped inspired by Disney's BDX droid, walking with reinforcement learning policies on a Pi Zero 2W.
Humanoidsintermediate by Antoine Pirrone and contributors (sponsored by Hugging Face and Pollen Robotics)
Exploded view
Tap any part to see where to buy it. Diagram is schematic, not to scale.
Every part you need
| Part | Qty | Spec | Where to buy |
|---|---|---|---|
| Feetech STS3215 7.4V, 19 kg.cm (C001, 1/345 gear) leg, neck, head servos | 14 | 7.4V class; BOM note: buy the 7.4V version also sold as 19 kg.cm; BOM lists EUR 14/unit on Alibaba 5 per leg plus 4 in the neck and head; the walking policies were identified on this servo. | Seeed Studio: $20.00 OpenELAB: EUR 23.57 Akizuki Denshi: JPY 3,200.00 RobotShop: $34.32 Alibaba: check price (unverified) single; BOM link |
| Waveshare Bus Servo Adapter (A) / Serial Bus Servo Driver Board servo bus controller | 1 | USB to TTL bus board; BOM lists EUR 5 Links the Pi to the servo chain and passes battery power to the servos. | Waveshare: $4.99 |
| Raspberry Pi Zero 2 W onboard computer | 1 | BOM lists EUR 26.08 Runs the ONNX walking policy onboard (Open_Duck_Mini_Runtime). | Adafruit: $19.05 |
| microSD card (SanDisk microSDHC in BOM) storage | 1 | BOM lists EUR 10 Holds the Pi OS and runtime. | Amazon: check price |
| BNO055 9-DOF absolute orientation breakout IMU | 1 | BOM lists EUR 40 (Amazon); maintainers note cheaper clones exist but are untested Gives the policy body orientation; mount it in the natural orientation noted in the assembly guide. | Adafruit: $34.95 Amazon: check price |
| SS-10 micro switch foot contact sensors | 4 | Two per foot, press fit; BOM lists about EUR 1 each Tell the controller when each foot touches the ground. | AliExpress: check price (unverified) BOM link |
| 9g micro servo antenna servos | 2 | BOM lists EUR 3.33 each (Miuzei pack on Amazon.fr) Drive the two expressive antennas on the head. | Amazon: check price |
| 18650 Li-ion cell, high drain (Molicel INR18650-P30B 3000 mAh 30A in BOM) battery cells | 2 | 2S pack; BOM lists EUR 5 each; buy the highest-drain cells you can Power for 14 servos and the Pi. | NKON: check price (unverified) single; BOM link |
| 2x 18650 cell holder battery holder | 1 | BOM lists EUR 4.99 Holds the 2S pack in the body. | Amazon: check price |
| 2S BMS board battery protection | 1 | BOM lists EUR 8.40 (shortened link in BOM) Protects the 2S pack from over-discharge and short circuits. | no verified seller yet |
| UBEC 5V step-down (HENGE 4A to 12A UBEC in BOM) 5V supply for the Pi | 1 | BOM lists EUR 4 Feeds a steady 5V to the Raspberry Pi from the 2S pack. | Alibaba: check price (unverified) single; BOM link |
| Small power switch power switch | 1 | BOM lists EUR 4.49 (pack; need one) Main on/off. | Amazon: check price |
| USB-C charger board charger | 1 | BOM lists EUR 9.99 (pack; need one) Charges the pack inside the robot. | Amazon: check price |
| 2.1 mm barrel jack, male connectors | 2 | BOM lists EUR 1 each Power leads into the servo board. | Amazon: check price |
| XT30 connector pair connectors | 1 | Need one male/female pair; sold in bundles (BOM lists EUR 8 for the bundle) Detachable battery connection. | Amazon: check price |
| Micro USB to USB-C cable, 15 cm cables | 1 | BOM lists EUR 7 Pi to servo board, short run. | Amazon: check price |
| Micro USB to USB-C cable, 50 cm cables | 1 | BOM lists EUR 6 Second USB run inside the body. | Amazon: check price |
| Cable sheath cable management | 1 | BOM lists EUR 9 Keeps servo wires tidy through the legs and neck. | Amazon: check price |
| Bearing (Amazon.fr listing in BOM) bearings | 3 | BOM lists EUR 3.50 each; size per the linked listing Fitted in trunk_bottom and the head to support rotating joints. | Amazon: check price |
| M3 heat-set inserts for 3D printing fasteners | 1 | Kit; BOM lists EUR 5.99 Nearly every printed part screws together through M3 inserts. | Amazon: check price |
| PLA (about 500 g) plus a little TPU filament | 1 | BOM: about EUR 20 of PLA; TPU only for foot soles Body, legs and head in PLA; feet bottoms in TPU. | no verified seller yet |
Quantities follow the official Open Duck Mini v2 docs: https://github.com/apirrone/Open_Duck_Mini/blob/v2/docs/assembly_guide.md. "Unverified" prices come from search listings or older BOMs that we could not confirm on the seller's product page.
3D printed parts
Needed. PLA at 15% infill for everything except foot_bottom_tpu (TPU at 40% infill). The print guide lists every STL and its count; a Bambu 3MF is also offered. Files: https://github.com/apirrone/Open_Duck_Mini/tree/v2/print
Mistakes builders make
- Gear ratio is debated: the BOM's '7.4V, 19 kg.cm' points to C001 (1/345), but two builders in issue #48 report the C001 is too slow for a smooth gait. Check the issue before ordering 14.
- 12V STS3215 servos need different simulation parameters; one builder on 12V/30 kg.cm servos got trembling feet with the stock policy.
- A contributor recommends Waveshare's ST3215-HS (106 RPM) if you buy Waveshare-branded servos; the standard Waveshare ST3215 is slower.
- A full 2S pack reaches 8.4V and the servo board does not regulate it, so the 7.4V servos see more than their nominal voltage (issue #51).
- Balance both 18650 cells to the same voltage before putting them in the holder.
- The trunk screws are M3x10, not the M3x6 an early assembly guide said.
- Configure each servo's ID before assembly; the maintainer used the LeRobot motor configure script.
- Use threadlocker on metal-to-metal servo screws, never on the plastic screws.
FAQ
How much does it cost to build the Open Duck Mini v2?
About $360 to $470 in parts at current prices, Official BOM totals EUR 398.10 at listed prices and EUR 331.10 at its 'lowest price' column, converted at roughly 1.10 to 1.17 USD per EUR. Optional expression package (speaker, LEDs, camera, mic) adds about EUR 34. Excludes a 3D printer, tools and shipping..
Do I need a 3D printer for the Open Duck Mini v2?
Yes. PLA at 15% infill for everything except foot_bottom_tpu (TPU at 40% infill). The print guide lists every STL and its count; a Bambu 3MF is also offered.
Buying guides for this build
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Last checked 2026-10-25. Sources: github.com · docs.google.com · github.com · github.com · github.com · github.com · github.com · github.com · github.com · github.com · github.com · www.adafruit.com · www.adafruit.com · www.waveshare.com · www.seeedstudio.com