I have been experimenting with Bullet. Specifically I was modifying the Hello World tutorial, to make the ball bouncing.
The first thing I noticed is, that I need to set both the restitution of the ball and the ground above 0 to make the ball bouncing.
For a simple setup, with two objects, this seems fine. However, for larger simulations I fell like, restitution is the wrong way, to make bouncy objects. Here are my reasons:
Consider three objects:
ground is just some plane.
box is a box, which is not supposed to be very bouncy, thus its restitution is near or equals zero.
ball is supposed to be bouncy, so I give it a restitution of
If now the ball collides with the ground, it only actually bounces, if the ground also has a restitution higher than
0, so let's give it a restitution of
1. So our ball is bouncy as expected, when colliding with the ground.
When it collides with
box it won't bounce, because the box has a restitution of
0. If we give
box a higher restitution, the ball will bounce from it. But now we have a different problem. If the
box collides with the ground, it will bounce off, but it isn't supposed to.
I see no way, with restitution only, to make this scenario work.
Restitution describes the amount of energy, that remains as impulse after a collision. The rest of the energy goes into deforming the colliding bodies and other side effects.
If we now look at a typical bouncy object, like a rubber ball, we see that they are easily deformable (compared to less bouncy objects). When the rubber ball collides with something, it takes up energy from the collision, by being deformed and then goes back into its original form, thus releasing the energy taken up during the collision and bouncing back off.
The solution (?)
Reason 2 suggests, that a bouncy ball (like a rubber ball) shouldn't have a restitution close to 1, but rather be elastic (thus being deformed and then going back to its original form), to model bouncy objects as expected.
The way to model this in Bullet, would be a soft-body and I think it would be the way to go, in such a scenario.
The actual question
The text above looks more like an answer than a question, so here's the question I'm trying to ask:
I'm really unsure, whether this is right. Are soft-bodies really the better way for bouncy stuff or am I just mistaking the principle of restitution?