In Isaac Sim, in the ROS MoveIt sample with the Franka panda arm: https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/sample_ros_moveit.html#isaac-sample-ros-moveit
Motion planning fails with the error:
Found a contact between ‘panda_link8’ (type ‘Robot link’) and ‘panda_hand’ (type ‘Robot link’), which constitutes a collision. Contact information is not stored.
[ INFO] [1628173366.292272163, 158.484643912]: Collision checking is considered complete (collision was found and 0 contacts are stored)
[ INFO] [1628173366.292302264, 158.484643912]: Start state appears to be in collision with respect to group panda_arm
[ WARN] [1628173366.326134548, 158.539172911]: Unable to find a valid state nearby the start state (using jiggle fraction of 0.050000 and 100 sampling attempts). Passing the original planning request to the planner.
[ INFO] [1628173366.326817695, 158.539172911]: Planner configuration ‘panda_arm’ will use planner ‘geometric::RRTConnect’. Additional configuration parameters will be set when the planner is constructed.
[ WARN] [1628173366.327349362, 158.539172911]: RRTConnect: Skipping invalid start state (invalid state)
[ WARN] [1628173366.327419452, 158.539172911]: RRTConnect: Skipping invalid start state (invalid state)
[ WARN] [1628173366.327498493, 158.539172911]: RRTConnect: Skipping invalid start state (invalid state)
[ WARN] [1628173366.327559874, 158.539172911]: RRTConnect: Skipping invalid start state (invalid state)
[ERROR] [1628173366.327615935, 158.539172911]: RRTConnect: Motion planning start tree could not be initialized!
After some digging, the cause is that the latest ROS melodic franka_description package has in the urdf a link ‘arm_link8’ with collisions defined. However, the collisions don’t exist in the Isaac example urdfs: (omni.isaac.urdf/data/urdf/robots/franka_description/robots/panda_arm.xacro).
Removing the collisions from the ROS franka_description package seem to temporarily fix the issue and motion planning works.