What I'm trying is to have a food tray, moving from point A to B, with small balls on it. Once the tray moved, the balls would get “carried” and then maybe roll on the tray and even fall out .

My question is how should I “carry” the small balls with the food tray at the beginning. Then, “activate” the gravity force to affect?

I am afraid I'm imagining this to be easy but I just can't come up ideas make it work. First, I realized that if I have all the balls in a geo node, it would fall as one piece all together. Second, if I turn off activation the whole thing disappeared. Also, the RBD balls just don't react to the moving tray at all….

Please share some ideas with me….thanks!

Hi, I'm think there's no need to changing active attribute at all. If you do a correct sim what you want will happen.
Let me to setup a scene for you. will be back.

Here you are. this is with bullet solver you can achieve the same effect with RBD solver. and as you know there are lots of important factors for the final result look, like the tray shape, and the animation curves and …

I forgot that you should also rotate the tray a little like real life to force the balls to follow. and you should add rotational stiffness to prevent the balls to rotate.

Thanks, Mostafa! Meant to get back but got carried away….

I followed your suggestion and got another question while trying different things. Instead of the tray moving from A to B, I am trying out if letting the tray to “rock” back and forth with a basic sin function. The balls would “follow” a bit then all fall through the tray….. Not sure what I should do to keep them above the tray… ops:


Edit: I changed sub steps to 2 on dopnet, and balls are all on the tray now!! But I am not sure if that's the right fix to the problem?