I am noticing your robot is one of the old style toy robots.. but the toy robots legs dont bend at the knees.. only at the hips and from there pretty much rotate on a arc.


Anyways.. to try and help you.. it looks like you need to modify it up some perhaps.


This assuming I understand what you're asking. Wanting it to bend like a leg with a knee joint with out wierd deformation and keeping the "D" cyilnder still.