I’ve been experimenting with ZSphere rigging with some success but I can’t figure this out. I’ve been trying to rig this very basic dinosaur mesh. I’ve bound the mesh to the zspheres and when I bend the whole leg from the hip it moves nicely but when I try to bend just the lower leg, from the knee it bends like a spring instead of a hinge. It’s as though the mesh is bound at the hip and ankle but not fully bound at the knee. Any idea what I am doing wrong?
you need to have a “double hinge” at the knee.
Make the top of the knee a sphere and the bottom of the knee a sphere. It should deform better that way.
Thanks for the suggestion but I just tried it and it made no difference 
The mesh topology is to low in vertices count to allow for an articulated pose.
I recommend that you bind one sub div level higher.
Alternatively, if you need the mesh topology to be very low in poly count, then you can reduce the Tool:topology:TopoSmooth to 1 or zero and then bind the mesh.
That was it, thanks very much!