why would adding a bone alter a FBX animation?

WendyLuvsCatz

I imported some Meshy3D figures rigged with Mixamo with unrigged tails

so added a child bone to the hip

selected the tail and filled with weightpaint and smoothed junction

all fine, it bends

additional info CANNOT ever memorise rigging on my Mixamo FBX imports or it will destroy it so don't suggest that 

but

now it spins on the hip playing the animation

my other solution will be to create a morphloader tail morph but the rigging should have worked

mikael-aronsson

If there are no keyframes on the new bone (and nothing else controlling it), it will not move in relation to the parent, not sure what you mean with "spinning" but check and see if it actually move/rotate compared to the spine bone, if it does something must be effecting the bone, not sure what that could be though, make sure rest position and so on have been set correct, but if it works fine bending the tail manually that should not be the problem.

WendyLuvsCatz

cloudflare obliterated my lengthy reply

I haven't touched the timeline, just added and weighpainted a bone

it has no keys

the hip it is a child of changes it's animation spinning on all axis

nonesuch00

Don't connect the bone to the existing rig, but make it independant and anchored to a null node or something you use to lock the attached end to following the hip bone and then animate it seperately. You can then re-use the tail animations on whatever creature you care to by reusing the tail you made them for.

Same concept if you want to animate hair, jewelry like necklaces & such, scarfs, ties, ...

I think that will work for you.

WendyLuvsCatz

I did solve it by simply weighting it all to the hip first then using a morph

its not behaving as expected simply because it's an FBX import and not a DAZ or Poser rigged item

I wager a lot of information is missing natively rigged stuff has under the hood

until recently one couldn't even import FBX unmangled and one still cannot pose most of them manually 

bones float in strange places, don't pivot as expected etc, the one thing that does work is animations saved from the same rig work on others the same such as Mixamo ones.

other than that it really is an import as is functionality