Encountering bug with Physics Asset UE4.26

I’m trying to build a vehicle with dismemberable parts, based on a previous system I made for insectoid characters, which work fine.

Unreal’s collision creation tools weren’t working with the precision I wanted so I used the “Copy Collision from Static Mesh” method.

I’m encountering this weird bug where all physics bodies snap to the location of the root bone when simulated

The bug doesn’t appear if all the bodies are created using Unreal’s tool:

However, despite all this, the meshes still snap to root bone when simulated in game.

I use this code to simulate all meshes except the root:


If I simulate from the root, then the issue doesn’t happen:


Additionally, when this happens, the collision of the mesh remains in place, though undetectable:

Really confused as to why this is happening. The issue is with the mesh itself because I isolated the mesh into an empty actor and simulated it the same way and the same issue happens.

I’m guessing my problem is related to this post: https://forums.unrealengine.com/development-discussion/animation/1642912-problem-physics-asset-default-physics-bodies-are-snapping-to-kinematic-ones-when-simulation-is-on

But that post has been lost to time :cry:

This primarily happens when I use the Break Constraint node, even though there is no constraint in the physics asset.

It seems that all bones just parent to the right cab door, every time for no apparent reason, and only their location is locked, rotation is free, and the original collision still seems to persist but it’s not visible when shown through the console command “Show Collision”

bump please!

This answer in this post solved the issue Some Simulated Bones Snapping to Root Bone - #8 by ProzackPH7

TLDR: Blender unit scale needs to be set to 0.01, then your armature and mesh need to be scaled back up by 100 units, export, import to unreal as a fresh copy, don’t reimport.

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