Stretchy IK

Hey up!

I’m trying to an IK rig for a jointed, telescopic arm (well, neck actually, but irrelevant.) The arm should obviously not be able to shrink beyond its rest position - it should only telescope outwards. It would be preferable if a stretch limit could be imposed, too.
Because I am animating a mechanical object, the rig will either need a duplicate set of bones to be the object parents, or to use copy location constraints on the objects, since I don’t want the actual objects to scale. This, however, shouldn’t be a problem.

I’m rigging this thing like a finger, so there is an IK chain for the actual arm, and one bone has a locked track constrant to point it at another bone. The rig is then controlled by one bone which goes the whole length of the chain, and can be scaled down to bend the chain.
In essence, therefore, I would like mancandy’s fingers, but where scaling the control bone upwards beyond the end of the finger would actually pull the joints apart :slight_smile:

For what its worth, I’ve crudely managed to do this for the last joint in the chain (using the finger rig for comparison, the fingertip comes away) with a track to constraint on a bone pointing back along the finger. This, however, cannot have an upper limit, and would not appear to be duplicable onto the other bones in the chain.