Regarding the unstable mecanum wheeled drive robot
Detailed Description
I’m developing a mobile manipulator robot called rb-Kairos. For its drive system, I used Mecanum wheels from the O3dyn project. However, when I run the simulation, the robot begins to bounce in place, and after a couple of minutes, it suddenly launches into the air. I suspected this was a collision issue, and upon inspection, I found that all the wheel rollers were using triangle meshes for collisions. I converted these to convex hulls, which helped reduce simulation crashes, but the robot still behaves erratically in a similar way.
@rosterlion0 i am just another user, but there’re some good suggestions in an old thread that i think explains some of the behaviors and potential approach when dealing with the sim accuracy issue you are seeing:
If interested, feel free to check out the assets in /Isaac/Robots/Fraunhofer/O3dyn (from the content browser) to evaluate how the mecanum wheels were set up.
even though convex hull did help to address some issues, it may not be sufficient to yield a desirable result still.
I went through it, but since I am a begineer to Isaac sim, I didn’t got what mistake I have made. I have recorded the complete process what I have done for a wheel so that you get an idea.
imported O3dyn >> duplicated the whole omni wheel >> arranged it into my robot >> created revolute joint with the base link
The bouncing is commonly due to incorrect collider setup, improper mass/inertia settings, or poor wheel contact/friction parameters.
Common Causes
Collider Misconfiguration: Mecanum wheels often require precise collision geometry. If the collider doesn’t match the visual mesh or overlaps with other parts, physics calculations become unstable, causing bouncing.
Improper Mass/Inertia: Unrealistic or unbalanced mass and inertia tensors can result in abnormal dynamics, especially during contact or minor disturbances.
Excessive Joint Stiffness or Damping: If drive or suspension parameters (stiffness or damping) are too high/low, or missing from wheel joints, oscillations and divergence from the physics engine may occur.
Erroneous Wheel Friction Parameters: Mecanum wheels need carefully balanced lateral and longitudinal friction. Too high or mismatched friction coefficients can cause excessive force buildup at contact points, leading to pops or launches.
Physics Timestep Issues: Running the simulation with too large of a time step or insufficiently frequent physics substeps can make high-speed contacts unstable, triggering unexpected “explosions”.
Recommendations
1. Collider Tuning
Check for collider overlaps at rest, there should be minimal intrusion into the wheel, axle, and ground.
2. Mass and Inertia Correction
Ensure the wheels and chassis have physically realistic masses.
Ensure the inertia tensors are computed from actual geometry, not default settings.
3. Joint And Suspension Parameters
Apply suitable damping to the wheel and drive joints (e.g., in Isaac Sim, use the damping property on revolute joints).
For articulated robots, consider simulating suspension or spring-damper elements to absorb shocks.
4. Friction and Contact Properties
Use friction pairs in NVIDIA PhysX or define explicit lateral/longitudinal coefficients as supported in Isaac Sim.
The standard O3dyn parameters, if copied as-is, may not suit your robot’s weight/friction needs; try lowering lateral friction or matching to your setup.
5. Timestep and Physics Solver Adjustments
Reduce the physics time step (e.g., from the default 0.016s/60Hz to 0.008s/125Hz or lower), and/or increase the number of solver substeps.