How to stop my cubes from flipping over?

I am trying to make a conveyor belt for a VR game. I need it to push objects down the belt, while allow them to be picked up by the player and possibly placed on top of each other. The current system works but it causes the boxes to roll down the belt. If I lock the rotation it prevents them from rolling when the player throws them. How can i keep the rotation when thrown, but prevent them from rolling down the conveyor belt.

Try manipulating angular damping. Add a trigger box on top of the conveyor belt and increase damping On Begin Overlap, and decrease On End Overlap or when a cube is picked up.

hey there!
did you try to put a big value on your belts physical mat (friction).
as well as you might want to put a bigger mass value

What about unlocking them when the player throws them?

What i ended up doing was causing the trigger box above the belt to lock the boxes. Then I had my hands unlock them when they are picked up. That way they get re-locked if they fall back on the conveyor belt. Thanks ClockworkOcean!