# Bulletsolver actor inside actor

Hello there!

It’s my first time using the bullet solver to work with interacting objects and I am running into a problem I can not solve or find a solution to anywhere. I’m trying to create a big cylinder/tube and have a few objects inside of it. The tube is supposed to spin and the objects inside should tumble around. Kind of like a washing machine.

I was following a tutorial, creating an static actor with a big tube geometry and a dynamic actor with a circle. The circle is positioned inside the tube. Now if I start the simulation, the circle gets pushed out the front of the tube and falls down. I am unable to keep it inside the collision shape of the tube. How can I acchive this?

I attached a simple example. If you hit start sim on the bullet solver you will see the problem.

Thank you very much in advance!

Collision_test.3.toe (4.9 KB)

Hello @LaserAnimationMW,

i changed the Tube to be a Concave shape on the Actor’s General parameter page as well switched the Tube geometry to polygonal.
That got it working.

Hope this helps
Best
Markus

Hi Markus!

Thank you so much! That did solve the problem for me. And the solution makes a lot of sense Having a concave shape allowing things inside the geometry. I just couldn’t figure out that I had to set the geometry to polygonal… Thanks again!

Maybe a follow up question if that is ok. Do you know how I can apply a rotational force to the “outside geometry” (the bigger tube) so that the “inside geometries” (smaller tubes inside the bigger one, I have duplicated them 2 times) tubles around, like items in a washing machine? It seems like I can not apply a force to a static actor and if I make it dynamic it keeps falling down…

Greetings!

needed @eric.b advise to solve this properly.

This all starts with Concave Shapes being static which means we need to build the tube out of separate rectangle SOPs which get transformed (rotated) and then used as a compound shape and also setting the kinematic state to dynamic.
Next the Actor needed to be constrained using a Constain COMP selecting the tube actor and it’s body index.

With this we can now give the tube actor a angular velocity as well as increase the mass to some very high value in order to have it not be affected by the colliding boxes.
For the colliding actor and the tube increase Friction and Rolling Friction to some value that makes the system feel right to your needs. As the units in relation to gravity are in meters, perhaps this is a massive washingmchine - so maybe scale down things a little if it feels too sluggish.

I’ve also added to Circle SOPs in the actor holding the tube to prevent boxes from falling out.

Hope this helps
cheers
Markus
Collision_test.4.toe (7.4 KB)

1 Like

WOW! Thank you so much for all the help and solving this problem for me! Both @snaut and @eric.b ! This is exactly what I was looking for and I would have never been able to come up with this solution, but I have a much better understanding on how the bullet solver works now. You helped me out tremendously

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Actually there is one more question that comes to my mind…

I would like to use the geometry after it has gone through the simulation and I am wondering how can I get it “out” of the bullet solver. For example: I would like to have a few tumbeling object and draw their outlines using a laser. In order to do that I need to “export/output” the objects with their simulated position as a SOP so I can put it in the Laser CHOP. So far I was unable to do that. I tried using an out inside an Actor and an Out inside the Solver. This way I can forward the initial base geometry, but only without the influence of the simulation. How can I get the simulation geometry?