Quaddle simulator : is there a URDF/MJCF model with leg spring compliance, and is the underlying physics engine documented?
#1
by robomotic - opened
I'm evaluating the Quaddle browser simulator (petoi.com/pages/quaddle-robot-dog-simulator) for use as a sim-to-real testbed for on-robot RL research. A few questions:
- Model export: Is there a URDF, MJCF (MuJoCo), or SDF description of the Quaddle robot available anywhere (even unofficially), or is the simulator's kinematic/dynamic model closed-source and only accessible through the browser UI?
- Physics engine: What physics engine/backend powers the browser simulator (e.g., a JS physics engine like Cannon.js/Ammo.js, or a custom kinematic-only solver)? Is it running full rigid-body dynamics, or just forward kinematics for gait visualization?
- Leg compliance: The hardware leg is described as "one motorized joint" per leg — is there any passive spring, elastic element, or series-elastic actuation in the physical leg linkage? If so, what's the spring constant / preload, and is it modeled in the simulator at all?
- Joint/actuator parameters: If the simulator does model dynamics, what are the joint stiffness, damping, and torque/velocity limits used for the servo model? Are these based on measured servo characteristics (e.g., stall torque, no-load speed) or nominal datasheet values?
- CAD/mechanical drawings: Are CAD files (STEP/STL) for the Quaddle leg mechanism publicly available, even without a full URDF? This would let me build my own URDF/MJCF with the correct link geometry and inertial properties.
- Sim-to-real fidelity: Has Petoi validated the simulator's gait output against real Quaddle hardware (e.g., tracking error, contact timing)? Any published comparison would help me judge whether it's useful beyond a teaching/demo tool.
- Roadmap: Is there a plan to open-source a proper simulation model (URDF/MJCF/SDF) for Quaddle or future OpenCat-based robots, given the existing OpenCatEsp32 repo doesn't include one?
Context: I'm building a MuJoCo-based hardware-in-the-loop pipeline for real-time on-chip RL (ESP32) and want to know whether Quaddle's simulator can serve as a physically accurate proxy, or whether I need to author the model from scratch.