Each wheel is now a hub solid + 8 passive HingeJoint rollers (capsules
tilted 45° in body xy plane at the bottom contact point) instead of
a single plain Cylinder. The rollers free-spin around their tilt axes
so the wheel exhibits mecanum X-pattern behaviour: gym-frame strafe
commands now produce body strafe in Webots, where before they
produced wrong-direction motion (the plain cylinders behaved as 4-
wheel skid-steer).
Calibration on flat field, 200 steps each:
gym predict webots out err
vx=0.5 vy=0 1.33 m/s +x 1.19 m/s +x 10.9% +x
0 m/s +y -0.10 m/s +y ~clean
vx=0 vy=0.5 1.33 m/s +y 0.50 m/s +y 62.1% +y
0 m/s +x -0.37 m/s +x noticeable
mecanum
coupling
Strafe is imperfect (-x bleed-through, magnitude under-shoot) but
direction is correct and the platform is now omnidirectional. Forward
motion is high-fidelity. Tilt signs assigned so diagonal pairs FL+RR
and FR+RL share the same body-frame roller orientation (the standard
X pattern). Two contact-material names "MecanumWheelA/B" are kept for
diagnostic separation; both use the same isotropic Coulomb friction
of 2.0 with forceDependentSlip 0.005.
tools/run_webots.sh ships the matching contactProperties block on
every mecanum launch (re-emitted into the temporary world copy).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Johnny Fernandes