How to build Legolas (open-source biped)
10-DoF bipedal walker · Advanced
Build Legolas, David Doan's mini Cassie-style biped: 10 hobby servos, Raspberry Pi 4, PCA9685, MPU6050 and a MuJoCo model for learning locomotion.
Many actuators, custom wiring and real tuning work.
Our estimate, part-time
Price the BOM yourself
MIT
What is Legolas (open-source biped)?
Legolas is a small two-legged robot by David Doan, modelled on Agility Robotics' Cassie. It's meant as a cheap platform for learning reinforcement-learning locomotion, without the price of research actuators.
It walks on ten hobby servos, eight 40 kg·cm and two 80 kg·cm, linked to the legs through M4 rod ends in Cassie-like linkages. A Raspberry Pi 4 drives them through a PCA9685 board, and three ADS1115 ADCs read each servo's potentiometer so the controller knows the joint angles.
The repo holds SolidWorks CAD for three iterations, printable STLs for V2 and a MuJoCo model of an earlier version.
Legolas (open-source biped) specifications
- DoF
- 10
- Servos
- 8× 40 kg·cm + 2× 80 kg·cm
- Compute
- Raspberry Pi 4
- Sensing
- MPU6050 IMU, 3× ADS1115 for servo feedback
- License
- MIT
Figures as published by the project. See Sources below.
Bill of materials
| Part | Qty | Notes |
|---|---|---|
| 40 kg·cm digital servo | 8 | |
| 80 kg·cm digital servo | 2 | |
| Raspberry Pi 4 | 1 | |
| PCA9685 servo driver | 1 | |
| MPU6050 IMU | 1 | |
| ADS1115 ADC | 3 | |
| M4 rod ends and threaded rod, thrust bearings, ~1 kg filament | — |
Where's the full bill of materials?
The full BOM, with exact quantities and vendors, lives in the project's own files. Prices change often, so treat Not published as a ballpark. Start at the project repository.
Tools you'll need
- FDM printer
- Soldering iron
- Hex keys
Step-by-step build overview
Electronics & wiring overview
Pi 4 → I²C → PCA9685 (servo PWM), MPU6050 and three ADS1115s. The servos need their own high-current supply.
Software
MuJoCo model for simulation and Python control on the Pi. The second XML in the repo is Agility's Cassie reference model, not Legolas.
Tips from the bench
- ☕ The MuJoCo model is an older version, so check dimensions against V2 before trusting sim results.
Legolas (open-source biped) FAQ
Why Cassie?
Cassie's leg linkages are well studied for dynamic walking, and Legolas copies that layout at hobby scale.
Is there a cost?
No total is published; the README lists parts with Amazon links.
Sources
Written by Bots n' Beans from the project's own documentation. Check the sources for the latest revision before you buy parts.
Related builds
Robot deals
All deals →
Get dealDeal · Everblog
10% off
ShopShop · CircuitMess
DIY robot kits
Robot and gadget kits you build yourself.
ShopShop · GRABO
Cordless vacuum lifter
GRABO Pro Brushless: the original cordless vacuum lifter for pavers, stone, glass and panels.
Like what we do? Buying through these links supports Bots n' Beans. We earn a commission at no extra cost to you. Thank you!