I have a bendy bone for a spine, and I want to attach limbs along the length of the spine. I want the base of the limb to follow the point of the bendy bone that they’re close to, is there any way to attach a bone so that it inherits the shape of the bendy bone rather than the position of its tip or base?
This is the rig. I want the dorsal and pectoral fins to attach to the middle of the bendy bone and inherit any flexing:
I tried using a copy transforms constraint with the head/tail setting set to a proportion of the bendy bone, but it worked as if the bendy bone was a normal straight bone.
Will I have to implement this with drivers? The way I see it could be done is to add a pair of bones to the base and tip of the spine controls and then use the formula for a quadratic Beziér to mimic the bend of the b-bone, but this seems pretty tedious, given that the whole idea of this rig was to be quick and simple
Had a plan B, which works as a cheap-n-cheerful fix, but falls apart if you stretch the bendy bone too much. I made the handles and put a bone in the middle with a damped track constraint on it to act as the parent for the dorsal. You can adjust the influence by changing the length of the red handle bones. Would still love to know if there’s a proper solution for this though, I use bendy bones a lot and run into this all the time.
So I looked at the manual for the constraint target as @Hadiscus suggested, and indeed I can use the mesh for a copy position constraint target.
So I made a vertex group on the mesh I’m deforming called dorsal.base, and assigned a vertex to 100% at the position where I want the base of the dorsal fin to be.
Then I added a copy position cconstraint to the dorsal bone, and used the deformed object as the target, with the dorsal.base vertex group. This has the effect of gluing the bone to the mesh at the right position, and it respects the flexing of the bendy bone, so it’s almost 100%, the only problem is that there’s a circular dependancy: the bone that is glued to the mesh also deforms the mesh to which it is glued which affects the psotion of the bone and so on. So it’s jittery and janky.
Oh, and it doesn’t pick up the rotation of the mesh, even if I select a few vertices around the point I want to attach the bone. So close, but no biscuit.
Thanks, that works perfectly. The only tricky bit is that you have to calculate the exact head/tail ratio for the attached bone to get it in the right spot at the rest pose.
