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Troubleshooting Common Physics Asset Errors

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While there are a number of things that can be out of your control during a physical simulation, there are two issues that are definately within your power to correct: Exploding (interpenetrating physics bodies that are set to collide with eatch other) and Jitter (when the Physics Bodies refuse to sleep due to micro movements). Below are some steps for correcting these issues.

Exploding

This is caused by two Physics Bodies interpenetrating and the physics system attempting to correct it by applying a massive amount of force to expel the Physics Bodies from each other. If a Physics Constraint is keeping the offending Physics Bodies together, the physics system will continually apply force to separate them, causing very erratic and extreme movement.

brokenPhAT.png

This is normally fixed by disabling collision between the two offending Physics Bodies, or changing their positions and/or scale to make sure they do not interpenetrate. Also, welded Physics Bodies act as one regardless of interpenetration.

Jitter

If the Physics Asset is mostly "collapsed" but still shaking and twitching on the ground, but not violently bouncing around, there are a few values you can tweak to get it to stop and sleep.

Before doing anything, try simulating with No Gravity, this will show you if any of your Physics Constraints are miss aligned and trying to correct before the Physics Asset has even hit the ground.

Often times, a small amount of Linear and Angular Damping on all the Physics Asset's Physics Bodies is more than enough to stop the asset from shaking. However, using large values in Linear Damping will cause a Physics Body slow its movement through the world, even due to gravity. Damping, as it is implemented here, is not "drag" per se. It is more like moving through a viscous substance.

If jitter is still an issue, perhaps you have a number of really small Physics Bodies, check the Substepping documentation for information on having the physics simulation calculate in-between solutions.

See the Physics Asset Properties Reference and Physics Constraint Reference for more details on the properties for Physics Constraints.