Notes on Bullet

Bullet "Friction" appears only in surface direction and this prevents objects from sliding over the ground, the maximum is 0 velocity in surface direction and thats in the scene to see.

If you look closer to the collision point you see no movement in surface direction, but the object can tilting around this point, therefor the cube and the sphere begin to roll. The friction doesn't prevent objects to lift from the ground. That's a different force like adhesion that Bullet doesn't support.

You can select other BT joints and when "Affect" is on they follow every editing in this joint, so you doesn't step explicit to every joint to make the same change in there values. 

Bullet Settings


Controls how much "force" is applied to particles who are penetrating.

This can cause "explosions" if particles penetrate.

Recommend setting ERP to 0.1 (or 0.01 if needed).

In some cases, setting ERP to 0.0 can result in no collisions at all, so we recommend avoiding 0.0.

Linear Slop

Linear Slop is the amount of permissible interpenetration between colliding particle meshes in world units.

Larger values appear to cause the sims to require additional time.

Recommend setting Linear Slop to 0.1

Size As Mass

This gives an automatic mass calculation that is based on the size of the particle and overrides any mass given to particles anywhere in the tree.

If objects are having interpenetration problems (e.g. falling through the ground), leave this UN-checked and use Size as Mass nodes relative to each group; it seems to solve most interpenetration issues.

State Settings

Recommend setting "neutron" groups to "Static" and not to "Kinematic".

Kinematic sometimes causes explosions if particles penetrate (even if ERP is really low).

BT Joint Helpers

You can select other BT joint helper objects and when “Affect” is on they will all inherit the same values.

Rope Pivot

The pivot is simply set, when instead a shift with velocity TP takes automatic care about the sub-sample position.

For example, you have a rope with fixed ends. So you can see the pivot in the middle will be corrected but when this translation is done with velocity and a time between two sub-samples will requested TP shift the whole rope as static object with this velocity out of the fixed position. 


Bullet Softbodies are animated in object space and every vertex has it's own velocity, so the particle Velocity is undefined.

When TP has particles with velocity it automatically makes a linear sub-interpolation between two sub-steps, therefore the whole softbody would be shifted incorrectly.