Vehicle Part Animation/Physics Bug?


I think some others have talked about this before, but I am wondering if this is a true bug or what?

I found out that if I constrain a physics box/Car Door to the root node of my skeleton,
I can animate it/enable/disable physics without “issue”… HOWEVER, my vehicle is stuck to the ground and I cannot move/drive.

But, if I constrain the door to some other random part of my skeleton, the door can animate fine, but then Enabling Physics causes the door to fall off… heh…
Then when I re-trace to that piece that fell off , it re-animates, it snaps/attaches back to the car, and closes back up. haha. But that is probably something else I have to fix.

Do I need to maybe create a dummy/empty node for the root in 3DS Max, then attach my chassis geo to that? Then everything else to the chassis?
Then in UE4 , link the collision/constraints to the chassis?

Root (Dummy)

Right now it’s one thing or the other.
Animate the doors properly/can drive, but door fall off from Physics Enable. Or animation/physics work fine, but car can’t move…

I should probably also condense some stuff, to reduce joints I won’t use.

I setup a hierarchy in 3DS Max via linking, with my root(Belair) at 0,0,0, which is a piece of geometry. Then everything is linked to that.
I then Exported as FBX, and imported as a Skeletal Mesh, from Max 2016.

Any info. would be great, thanks!!

I do have my Root at 0,0,0, but the geo is centered around 0,0,0, and not above. Someone said in another post that might be why. So I can give that a shot.
The Chassis is through 0,0,0 and wheels are below.

I had it setup that way for GTA IV / Outerra Engine, which worked ok. I think that was how it had to be for the COM (Center of Mass).


Tried linking the Main body to a root node/bone, then linking the doors to the main body. But I still have the same issues.
This really seems like a bug. Also the Angular Limits seem broken too maybe.

I will try doing 1 more thing in Max with the “skeleton” and re-import. If still acting up, I’ll make a video.

Here’s a video showing the issue. Compression isn’t the best…


Edit: Been experimenting with Sockets, we’ll see what this does. So far I can spawn/attach a mesh to my car, then detach and enable physics, or enable physics while attached and it works fine.
But I need to see if I can properly attach/simulate a socketed piece, and have it rotate how I want, then potentially break off with enough force.

I was able to Trace to a Socket Static mesh this morning in a test. Then animate with a timeline in the same way I do my Skeleton Joints. So that is promising.
Now I have to test the physics sim on those attachments and see if that works or not…

If it will sim and respect the position and rotation locks, and not pin down/interfere with my vehicle, I think I might be good to go!..

It sounds like doing socket/attachments is better than creating a ton of skeleton joints anyways.
So I might reduce my skeleton alot, and only have maybe 5-10 bones in total, then do most everything as Sockets.

So I can break off doors/trunk/hood/bumpers/side panels/ect.
Then hopefully setup Morph Targets on those attachments, so I can detect collision and damage over time, besides physics sim/detachment.