The four mjbots qdd100 servos alone cost about $3,500, so the parts total is around $4,500 before printing.
Upkie is a knee-high wheeled biped that balances on two wheels like an inverted pendulum and uses two-joint legs to crouch, absorb bumps and handle uneven ground. It runs on mjbots brushless actuators and a Raspberry Pi, with a Python and C++ software stack whose Gymnasium environments control the simulated and real robot with the same code. It was started by Stéphane Caron and is used for reinforcement learning research at Inria.
At a glance
| Parts cost | $4,600 estimated How Estimated for this page from current retail prices (2026-10-02) of the parts in the project parts list source ↗ Build priced Standard Upkie from the bill of materials (4 qdd100 servos for hips and knees, 2 moteus r4.11 developer kits for wheels) Not included 3D printing filament, tools (including the 3D printer listed in the parts list), shipping, tax; the computer used for development |
|---|---|
| Difficulty | 4/5 Advanced · Assembly is mostly bolt-together printed parts, but it needs custom crimped and soldered cables, configuring moteus actuators over CAN-FD, and a budget of several thousand dollars for actuators. |
| Build time | Not stated |
| Tools needed | FDM 3D printer (PETG at 0.2 mm, the whole torso and both legs), soldering iron (XT connectors, battery springs), JST PH crimping pliers, heat-set insert tool (about 90 M3/M2.5 inserts), metric hex drivers |
| Motors | 4 mjbots qdd100 servos (hips, knees) + 2 mj5208 motors on moteus r4.11 developer kits (wheels) |
| Controller | Raspberry Pi 4 Model B with mjbots pi3hat (CAN-FD) and power dist board |
| Sensors | IMU (on the pi3hat, unconfirmed), servo encoders; optional OAK-D Lite camera mount |
| Published | ✓ Parts list✓ CAD/STL✓ Assembly guide✓ Wiring✓ Software✗ Video Doxygen docs site on GitHub Pages (six-step build guide, parts list and cables pages), FreeCAD/STL repo, GitHub Discussions |
| Activity | Last update 2026-10-02 · 436 GitHub stars · GitHub Discussions (about 100 threads, including a Real robots showcase), Matrix chat room, 57 forks |
| Kits | No commercial kit found; actuators and boards are bought from mjbots |
Licenses
| Design files | Apache-2.0 (upkie_parts repo LICENSE, FreeCAD and STL files) source ↗ |
|---|---|
| Code | Apache-2.0 source ↗ |
| Documentation | Apache-2.0 (docs are built from the main repo, covered by its repo-wide LICENSE) source ↗ |
Builder notes
Practical points from the project's issue tracker, forum and docs, each linked to its source.
- The qdd100 hip and knee servos now cost 879 USD each, roughly double their price when the project started. The software only needs moteus controllers on CAN-FD, so other actuator bodies can be swapped in, and the lead suggests a driverless CubeMars AK80-9 as an easier option than CyberGear motors. source ↗
- The 3D printing guide still lists 3MF project files and a torso made of face, head, side and back plates, but the parts repo deleted its 3MF files in March 2026 and now ships a single torso case plus upper and lower leg parts. Builders have to match the guide's part names to the current files and set print settings themselves (PETG, 0.2 mm layers, 20-60% infill per the guide). source ↗
- The specified 1:8 RC wheels with a 17 mm hex and 80 mm inner diameter are hard to find in some regions. The wheel hub FreeCAD file can be resized to fit other RC wheels, and a hex variant suits standard 17 mm RC drivers but is more brittle. source ↗
- Moteus firmware from June 2022 onward reports zero servo velocity on Upkies configured with older firmware, until the encoder source PLL filter setting is changed to a non-zero value. source ↗
Other wheeled plans
- Donkey Car · $250–$300 · difficulty 2/5
- LeKiwi · $480 · difficulty 2/5
- OpenBot (smartphone robot) · $50 (2020) · difficulty 2/5
- XLeRobot · $660 · difficulty 3/5
- F1TENTH (RoboRacer) autonomous race car · $3,000 · difficulty 3/5
- OpenMower · $790 · difficulty 3/5
- TidyBot++ · $5,200–$6,300 (2024) · difficulty 4/5
- NVIDIA JetBot · $640 (2024) · difficulty 2/5
- MuSHR racecar · $1,100 (2022) · difficulty 3/5