Issue with animating Model with Motor6D attached to Humanoid

Hello developers,

I’m trying to make an animation which incorperates a model, I have the model’s primary part set to a part which is welded to the right arm of my Rig.

Part 0 is the Right Arm
Part 1 is the PrimaryPart

Every other part in the model is welded to this part.
No parts are anchored

When I rotate the part, instead of rotating in place, it rotates the entire rig with it as well. But when I rotate the arm, it works as intended, the item moves with it. The problem only occurs when i try to move it independently.

I was wondering if anyone knows as to why this could be happening.

All help is appreciated!

Could be anchor issue, not sure though.

just animate it in blender
Set humanoid rig at origin, brief case on the motor6d position, export briefcase model (assuming you have a ready rig for humanoid) and then parent it and start animating
Done
No more manual animation slop