locked track constraint *with offset* on mechanical rig

Question

I want the swivel to follow so that the aim bone points at the target bone. using a "locked track" constraint. (dealing with the up/down aim elsewhere)

problems:

• it has to rotate from the swivel bone, but if swivel is aimed directly at target, then aim bone will be pointing just to the side of the target.
• you could offset the swivel's angle by a little, but it wouldn't stay correct as the target gets closer or further away.
• aim has to be a child of swivel (mechanical rig)

The only solution I came up with is giving the target bone a child that points back at the aim bone. Then, you transfer that angle to the swivel bone (flipping it upside down so the swivel gets the opposite angle). That works, but I'm probably missing some basic way to solve this without that complexity.

When trying to rig up mechanical arm machines, they often have this problem where the whole thing swivels from one place (the center), but by the time you get through a couple of arm sections, it is offset from the center.

any ideas?

Answer 1

I generally use IK for this kind of rigs.

In my example Aim Bone has a IK constraint targeting at Target, chain lenght 3.

Target is unparented to any of the chain bones.

The rest of the chain is parented connected.

Aim is stretchy and locked on all Axis.

Mid is locked on all axis.

Swivel is locked on X and Y axis.

Mesh is parented to Swivel bone only.

With this setup it's easy to implement vertical aim also: just unlock X axis of Aim, and add a copy of aim, which copies loc and rot from aim, and scale from Swivel.