Problems with Rigid Bodies and "Convex Hull Polytope" Bounds

Hello everybody!

(Hope this really belongs here and not in the Game Engine section)

I am rather new to Blender and I have now recently tried my first animation with rigid bodies and now I have some little problems with that animation.

I’ve basically turned my object into an actor and tweaked all its settings, as “Bounds” type I chose “Convex Hull Polytope”, since it is a toy amunition ring (I’ve posted a thread about modelling that somewhere else in the forum), which means it is neather a sphere, nor a box, but a more complex mesh.

Now I’ve alt-duplicated this object serveral times and let them all fall down on some plane and interact. The result is quite ok, but not really perfect. You can have a look here at YouTube.

As you can see the main problem is: The “Convex Hull Polytope” bounds are not calculated perfectly. In the end the rings are not really lying on the plane, they are rather flying a bit above it.

My question: Is there a way to get a more accurate calculation of these bounds? Or is there another easy way to fix this? The only thing I can think of at the moment is to change the camera position so I have a overhead shot in the end, so you wouldn’t really see that they are not directly on the plane and on top of each other.

Then one more thing about this animation: At a certain point the light suddenly gets a bit brighter. I really don’t know why, I haven’t animated any lights and it happens between two frames. Does anyone know what this could be?

Thank you in advance,


I am no expert on this… But here are some ideas.
at the bottem you can use a script to turn up the precision?

As far as the lights do you have double sided rendering on? I think that I changed that when I had similar flashing lights.

Hello ibkanat!

Thanks for your quick answer.

I found the python script at the bottom on the page, but now I am not sure how to execute it (first time ever using a script for me…). I typed in the text in the Text Editor window and then pressed Alt-P, but it gives me an error message. When I check the console now it tells me:

“Traceback (most recent call last):
File “Text.001”, line 1, in ?
NameError: name ‘GameLogic’ is not defined”

What am I doing wrong? Or do I need to start the game engine first?

Also: What do you mean by double sided rendering?

Thank you, MasterDomino

In the Editing Mesh window is double sided enabled?

I don’t know about that script I haven’t tried it sorry. You could post on the psyhics web site.

Hello again ibkanat,

about the lighting: The double sided button is enabled indeed, I will disable it and render it later and see if it helps. Thank you.

About the script: Is my way of executing the script correct at all? I type it in and then press Alt-P. If I did everything correct I will post that question on the physics web site, I guess.

Thanks a lot so far!


The script probably works as a Scriptlink.

I’m moving this to the GE forums where you’ll probably get more looks.


You have to load that script with python controller (logic panel) and connect the controller to always actuator (untick the button with three buttons).

@Fligh: Thanks for moving it.

How do I load the script with the logic panel? Sorry, I am really new to this… :o

Thank you!


Type the correct script name in the script box shown in attached picture. Note that always actuator has pulse mode on as default (button with three dots), so you should disable it because the script needs to run only once.