UE 5.0 Physics Inertia Persistence - major change from UE 4.26

Development World Creation
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1

I’ve been working on a game that is intended to have heavily animation-based movement, and physics-based animation. A large part of that is healthy usage of ragdoll behavior.

Unfortunately, when I converted my project to UE5, I found some major physics changes, which feel like it’s going to make upgrading a non-starter, unless I have some way to work around them. The biggest issue being, when a character enters a ragdoll state, due to being hit by some force, that force is no longer transferred onto the ragdolling character, which makes the physics behavior look really bad.

I made a short video showcasing some of the problems here: Unreal Engine 5 (EA 2) Physics Inertia Problems - YouTube (UE5 starts at 1m in. Beginning of video is 4.26 baseline)

For reference, in this video, the “ragdoll” effect is achieved by calling “Set All Bodies Simulate Physics” to true on the character’s static mesh component, and using the RigidBody node as the only input in the character’s animation blueprint. The behavior is very similar when calling the “Set Simulate Physics (mesh)” method on the object’s static mesh component.

Is this a known problem for Early Access / is this something on the team’s radar to fix before UE 5 launches? Or is this the new desired behavior?

I’m hoping it’s the former, because I was looking forward to using control rig and the latest version of full body IK in UE5

2

anyone know if this is a known issue that will be fixed at some point, or is this the intended behavior of the new UE5 physics system?

3

What I know is that UE5 uses Chaos, as opposed to UE4 which uses PhysX. These will behave differently, because they are totally different code bases.

Perhaps there is something in the ragdoll code of Chaos that starts with zero momentum when the mode is turned on? If you want to make sure that momentum transfers, then get the momentum (or velocity) of the actor before you set the mode to ragdoll, and then apply an impulse to re-apply that velocity after you’ve changed mode to ragdoll.