UE 4.20.2: Merging Bones while using Physics body

Development World Creation
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1

I have run into a strange issue while working with the physics body of my character.

When I simulate physics on the character, it runs fine.

252870-wholebodysimulation.png

But if I simulate just the legs of the the character, things start to get weird.

252881-normalcharacter.png
252881-normalcharacter.png339×612 166 KB

252882-simulatinglegs.png
252882-simulatinglegs.png269×601 141 KB

As you can see, the ends of the hip bone sort of merge together into one spot. Simulating a single leg of the character works fine, it is only when both are simulated at the same time does this happen.

I’ve tried disabling all internal collision and deleting the restraints.

I’m not sure if this is a physics body issue or a skeletal mesh issue, but re-targeted animations work fine with physics disabled.

While in the physics simulation it is one leg that is merged into the pelvis, when running the game both legs seem to be collapsed into the pelvis.

252883-ingame.png

2

I have the same issue, if I enable physical animations on my character, but not on my “stomach bone”, which is the root bone for the legs and the chest bone, so my character doesn’t go full physic ragdoll and stays still, both my legs merge on the stomach bone doing this one leg thing !! very anoying, and I’ve tried multiple things but nothing seems to solve this issue. PLEASE HEEELP !!!

3

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5

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6

For me, it’s hard to know what the issue is without seeing the asset myself. But here is some things to check:

  1. Make sure that every bone’s scale is 1 when you exporting and in engine. (export in cm units)
  2. Try to add bodies one by one to find where the problem occurs
  3. Check if your linear constraints turned off. (I assume you don’t need linear movement on human skeleton)

In case it doesn’t help, can you upload an example assets?

7

I’m using blender for modeling but I don’t know where to look for bone scale, as instead of being scaled, the position of the endpoints are changed.

If you remove the physics bodies on the thighs, then it will be the calf bone that ‘teleports’ to the pelvis, and if you remove the calf physics body, then the foot bone will teleport to the pelvis.

Linear constraints are off.

I have included my model
here.
If you are also using blender, you might find that the bones have weird orientations. This is for compatibility reasons with UE’s animations.

Thanks you!

8

So yeah, problem is the scale of the root bone which is 85.266…
I’ve scaled it back down to 1, imported to UE4 and rescaled to 85 in the scene and it works without issues. Usually you have to keep everything in scale of 1 to avoid this kind of problems.

9

Sorry, but I was looking back on the mesh in blender, and I can’t find the scale attribute for the life of me. All I have is head location, tail location, radius, roll, and envelope. I was wondering if you could point me to where it is located, Thanks!

10

I didn’t use blender much, but iirc the bone structure should be under armature.