Developer Notes

Duplicate of UE-50380


Small objects have erratic behavior when simulating physics. If drop at an angle, some will start spinning indefinitely on contact with the ground while others will spin in place when hit.

This is a regression:
Working in 4.15.3-3450819
Not working in 4.16.3-3561208

User Description:

I have physically simulated objects at various scales, the smallest are less than a cubic centimetre. The physical simulation used to work fine in versions up to 4.15, but since then the small objects behave weirdly.

Instead of coming to rest, objects that are smaller than ~4 cm³ keep spinning around a corner of the colliding surface. Turning on Stabilization (which was introduced in 4.16) and turning off PCM (which already exists in 4.15 and does not cause problems there) helps but doesn't eliminate the problem. I haven't found any configuration of physics parameters that completely removes the issue in 4.17, on the other hand no configuration I tried in 4.15 exhibits the problem.

Steps to Reproduce
  1. Open the attached project
  2. PIE
  3. (Some behavior will be apparently on play) Roll the ball into the cubes

Results: On play, some objects will be spinning on contact with the floor. After rolling the ball into other objects, some will start spinning in place.

Expected: For even small objects (within reason) to have realistic physics.

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ComponentOLD - Anim
Affects Versions4.
Target Fix4.19
CreatedAug 22, 2017
ResolvedNov 20, 2017
UpdatedJun 23, 2018