MuJoCable simulates cable-driven robots with realistic friction and routing
MuJoCable: Reduced-Order Surface-Routed Cable Transmission for Tendon-Driven Robots
RoboticsComputational Engineering, Finance, and Science
Summary
Robots that use cables or tendons to move parts can be tricky to simulate because cables bend around pulleys, stretch, and experience friction. The authors created MuJoCable, a tool that adds smarter cable simulation to the MuJoCo robotic physics engine. It calculates how cables wrap around shapes and how tension and friction change along the cable, helping predict how the robot will actually move. This helps designers test cable routes and forces in simulation before building real robots, making designs more accurate and reliable.
What this means in practice
- •For robotics engineers: Design and simulate complex cable routes with friction and tension effects before hardware fabrication.
- •For robot designers: Predict motion inaccuracies and tension build-up in tendon-driven robots for improved actuator and cable layout.
Authors
Yi Zhang, Qi Shao, Yicong Lin, Muyuan Ma, Tao Sun, Yue Xie
Abstract
Tendon transmissions reduce distal inertia and add compliance, yet routing, slack, and friction govern motion and force transfer. Mainstream rigid-body robotics simulators such as MuJoCo do not jointly resolve moving noncircular contact, unilateral tension, and segment friction. We present MuJoCable, which adds a reduced-order, configuration-dependent cable transmission to MuJoCo. Its routing algorithm jointly optimizes an ordered path across moving analytic and mesh surfaces. A unilateral axial law, directional Capstan propagation, and nodal virtual work map this path to segment tensions and body forces. The warm-started engine plugin applies these forces during simulation and exposes route and load states for design. Pulley benchmarks recover analytical transmission relations with a Capstan-ratio error below 0.5%. On the underactuated 18-joint SpiRobs, MuJoCable reveals friction-driven load growth and proximal redistribution of joint rotation that the native tendon does not represent. Hardware tests on SpiRobs and a tendon-route-coupled finger reproduce observed motion sequences. By making physical threading executable, MuJoCable brings transmission sources of the simulation-to-reality gap into route, cable, and actuator design before fabrication.