URDF description for the Upkie wheeled biped.
The description can be loaded directly in various Python robotics frameworks, for instance:
import upkie_description
robot = upkie_description.load_in_pinocchio()Check out the Python readme for more details.
| Joint | Limit | Value (±) | Unit | Why? |
|---|---|---|---|---|
| Hip | Position | 1.26 | rad | Geometry: cables fully stretched |
| Hip | Velocity | 28.8 | rad/s | Details below |
| Hip | Torque | 16.0 | Nm | Peak torque (< 1 s) from the qdd100 spec |
| Knee | Position | 2.51 | rad | Geometry: wheels touching hip actuators. |
| Knee | Velocity | 28.8 | rad/s | Details below |
| Knee | Torque | 16 | Nm | Peak torque (< 1 s) from the qdd100 spec |
| Wheel | Position | - | - | - |
| Wheel | Velocity | 111 | rad/s | Details below |
| Wheel | Torque | 1.7 | Nm | Peak torque from the mj5208 spec |
Peak velocities for the qdd100 are rated as 3,600 dps at 36 V and 2,300 dps at 24 V. Assuming a linear velocity-voltage relationship (which is a big assumption, for instance the actual maximum velocity will also depend on servo.pwm_rate_hz) leads to 1,650 dps at the 18 V of the RYOBI batteries used on Upkie, or equivalently 28.8 rad/s after conversion and rounding.
The maximum velocity from the mj5208 spec is 7500 rpm, or approximately 785 rad/s. Multiplying by the wheel radius of your typical Upkie (between 5 and 6 cm), we obtain a ground speed comparable to that of a car on a highway. We scale this down a notch! Backtracking from a top ground speed at 20 km/h, we obtain a maximum velocity around 111 rad/s.
- Upkie: main repository for the robot's hardware and software
- 3D printed parts: CAD files and add-ons for the robot
Upkie's torso derives from the chassis of the mjbots quad. The Apache 2.0 license applies to all files in this repository, to the exception of the wheel_tire mesh which is under the CC BY 4.0 license. Meshes from mjbots are also Apache 2.0. See the files in their respective folders for more details.