Unusual collision physics between thin parts.

Bug Reports Engine Bugs
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#1

I was trying to make a 2D game with very thin 3D parts (0.05 or less), but when I tested physics, this happened:
(Sorry I couldn’t upload the video file but here’s the place file: BugExample.rbxl (57.5 KB))

So, what happened was that when I unanchored them, the smaller part fall on the bigger one, and instead of bouncing or staying up straight, the part just went right through it and lay down on the ground. When I tried by making it fall from a very short distance from the bigger part, it didn’t go right through, but still didn’t stand up straight like it should. I also tried this again but after making it 2-stud thick, it worked until it was 200 studs high.

Expected behavior

The part should’ve stayed up straight either bouncing upwards or just staying, not falling to any side or rotating or going right through.

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#2

This is an engine limitation of the current collision detection system. Very thin parts can lead to tunneling. In your case, the contact resolves the penetration by pushing the part horizontally, since that’s is the path of least resistance. If the part is moving a lot slower (less gravity), then you can also see it work because there is less contact penetration at slower speeds.

Making the parts thicker is the best solution for now - you can always separate out your “physics” part from your visuals if your goal is to present a specific style.

Longer term we hope to resolve this with a new, continuous collision system, which prevents tunneling.

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