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Edge Physics/Collision bug


I am having issues getting a ball to roll smoothly on other objects.

See video: https://www.youtube.com/watch?v=Ydv3bLza2Ew

The ball rolls fine, but as it gets speed, it seems to hitch/glitch on the geometry. Sometimes it can even completely stop the ball from rolling all together. In the video, each time you hear the bump sound is when it's hitting(what I think) are the edges of the geometry, and this happens even on perfectly flat surfaces.

Here is the imported .fbx file: https://drive.google.com/file/d/12KduLoYUu6F6UX3cN0bCEVUO5Nd5xLkE/view?usp=sharing

In Blender the geometry is perfectly smoothed, and there are no hidden polygons inside of the object, so I'm unsure why the physics are catching on what seems like the edges of polygons.

CCD is enabled.

PCM is enabled.


Product Version: UE 4.18
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asked Jan 01 '18 at 06:16 PM in Using UE4

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2 answers: sort voted first

Bug is reported and confirmed by Epic. Track the issue and vote for it here: https://issues.unrealengine.com/issue/UE-74451

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answered May 13 '19 at 06:52 PM

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The rolling ball instability that you're experiencing is a common issue with physics engines. In your case, it's probably due to the default settings of Unreal Physics Engine and your surface mesh' quad size (they're probably too small). You need to tune some parameters of the Physics Engine to reduce such issues. In project settings, start by lowering these values: Min Contact Offset, Max Contact Offset. You can also try increasing Contact Offset Multiplier. Note that changing these values will increase the stability but at a cost of performance!

Hope this helps!

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answered Jan 01 '18 at 10:53 PM

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avatar image Crystal3lf Jan 02 '18 at 02:24 PM

Min Contact Offset and Max Contact Offset are set as low as they can possibly go, and Contact offset from 1, 100, to even 1000+ has no affect on it.

I'd also like to point out that its doing this even on flat surfaces.


avatar image Vizgin Jan 02 '18 at 05:04 PM

I'm sorry that your issue has not been fixed yet. I suggest you bump this post again or post a new one here or in the forums with a "bug report" tag so that Epic staff can take a look it. You can also report this directly to Epic and provide them with materials and exact steps so that they can reproduce this on their own machines.

avatar image ERuts May 08 '19 at 10:05 AM

Have you found any solution? I am having the same issue.

avatar image Crystal3lf May 08 '19 at 04:15 PM

Sorry :\ The only way to fix it is to create your own custom physics.

avatar image ERuts May 13 '19 at 06:51 PM

k. In the meanwhile I have issued an official bug-report which is confirmed by Epic. View and vote for it here: https://issues.unrealengine.com/issue/UE-74451

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