Issue with Fork Entering Pallet Hole when Lifting Pallet with Forklift


I am working on a task in IsaacSim where I aim to lift a real pallet in the simulation using the forklift asset provided by IsaacSim. I implemented the forklift maneuver, which is controlled using the ROS2 /cmd_vel topic, and the fork is lifted to a specified height using the /joint_command topic with sensor_msgs/JointState messages.

I am trying to lift the provided pallet using the fork, but the fork does not enter the holes of the pallet. As you can see in the attached video, it appears that the fork should enter the pallet hole, but it gets pushed back as if there is an invisible wall.

When visualizing the collision mesh, it seems there should be no collision; however, the pallet is pushed back regardless of the collision mesh. I am using the pallet usd asset from omniverse://localhost/NVIDIA/Assets/DigitalTwin/Assets/Warehouse/Shipping/Pallets/Plastic/RackableExport_A/RackableExportPallet_A01_PR_NVD_01.usd.
I have activated Rigid Body and Collider in the Physics settings, with the collision mesh approximation set to SDF Mesh. (When activating Rigid Body, only the SDF mesh showed a collision mesh similar to the pallet shape, while all other options appeared to block the holes.) Without activating the Rigid Body, the pallet remains fixed in place and does not get pushed.

I would like to know how I can make the fork enter the pallet holes and ensure that the pallet is carried on the fork when lifted.

Thank you.

I found the cause of the issue. The problem was that when setting the collider approximation of the mesh for the fork, SM_Forklift_OperatorCab_B01_01, to triangle mesh, the collision mesh was generated as a convex hull rather than as visualized.

When selecting triangle mesh for visualization, it appears that the fork’s collision mesh matches the fork’s shape exactly as seen in the video. However, in reality, a convex hull collision mesh is created, connecting the top of the forklift with the tip of the fork. I verified this by dropping an object onto the fork. This behavior is not intuitive and should be addressed in a future Isaac Sim update. (I am using version 2023.1.1, and this might have been updated in the 2024 version, though I have not checked.)

Changing the collision mesh approximation of SM_Forklift_OperatorCab_B01_01 to SDF mesh resolved all the issues as well. The SDF mesh provided a more precise collision mesh (almost identical to the visualized mesh) compared to the convex decomposition.​

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