[Bullet] Rigidbodies have crazy movement when used with joints

[ZX-WT]

Godot version:

3.0.2

OS/device including version:

linux mint

Issue description:

I try to make a simple ragdoll and the movement went crazy with bullet but not in godot physics. I think it has something to do with the size of objects.

I tried to test with default size collision shapes and rigidbodies with joints and the result is stable. So I guess it is related to the size as the collision shapes have the size pram smaller than 1 in the attach project.

Steps to reproduce:
check project , switch physics engine and run the scene

Minimal reproduction project:

BUG.zip

[akien-mga]

CC @AndreaCatania

[akien-mga]

Still valid in the current master branch.

[AndreaCatania]

I didn't have the time to check this yet. However the instability may come from the too small body weight.

[KoBeWi]

Still valid in 3.2.4 beta3
Changing mass doesn't fix it.