Rigid body Bullet sim questions

Game Engine Game Engine Support and Discussion
1

hey everyone
just started learning the bullet physics stuff with blender, but I don’t know much about how to do some stuff, so I have a few questions for you experts

  1. which bounds are good for which objects?
  2. what is the best way to set up gears?
  3. what is the best way to have a gear / flap supported above the ground (e.g. 2 boxes with holes and an axis on a gear?)
    edit
  4. how do you make a string type of thing for a pulley system?
    thanks, any help is appriciated:)
2

to make gears, You need compound bounds, in the 2.43 previews. Just use a cylinder with the spokes of the gear as separate objects, parented to the cylinder. The easiest way to make a gear suspended is to use the Rigid body constraints in the 2.43 previews. Play around with types and variables until you have what you need (if you leave the text field blank, the gear will “attach” to the world at it’s center, if you enter an object in the field, that object will attach to the gear, with the pivot at the center).

Did any of that make sense?

[edit] oh, and the different bounds are good for objects similar to what they say they are, convex hull polytope being the shape of the model, but any dents or concave parts will be omitted. Static triangle mesh, as far as I know, is the same as making the object non-dynamic.

3

eh, sorta makes sense - but not really, still with 2.42
does anyone here have some tuts they can show me? particularly for something like a pulley?

4

well yes like he said convex hull prototype could be used for something like a chair that has no real basic shape. If you use the starting screen cube you should use box bounds because it will find all of the farthest points and make a box to connect them. It is pretty much the same for the rest of the bounds.

this probably dosent help a bit

5

I’m pretty sure you can’t do a pulley, even in the new builds. I believe the only way to use compund bounds, and the easiest way to use hinges, is in 2.43. just go to the object tab (F7), click on constraints, and choose “rigid body constraints”.
If you enter the name of an object, those two will be linked together as if by a hinge, if you leave the field blank, the object will be attached to that point in space.
play around with variables, and see what they do.

6

Bullet physics has only rigid body physics at the moment, not soft body physics. So you cannot easily simulate things like string, cloth, rope, etc. If you absolutely need a pulley, I would suggest trying some sort of tank tread type of setup instead of string.