I am in the process of learning how to rig. I have modelled a robot and I'm trying to rig the legs to move a certain way, but without any luck.
Please see the attached images.
Basically, I want point 'A' to work as a knee pivot, causing point 'B' and 'C' to close and come together when the leg bends (and vice versa when it moves outward). I want point 'D' to be a fixed position, with the leg moving forward, back, right and left from that point.
Whenever I have tried to rig the leg, point 'B' and 'C' have either stayed the same distance or just moved outward, and not inward.
This is just an idea but you will need to place the leg joint right int the centre of point A. Make sure that all the components are separate and do a Rigid Bind. Now when you rotate it should rotate around this point. The problem you are going to have as I can see is that you may get some penetration as you rotate. This can be corrected using a Set Driven Key with a Lattice on the geometry behind the knee. Or by using some other method. I hope that this has steered you in a correct direction. Good luck