Sometimes, when I’m making models, I make them up by eye with scissors and paper, other times, and this is one of those times, I use the computer to help me work out how things will fit together. Here, the main part I’m working out is the Cam Follower / Bell Crank piece. It’s the turquise pie slice above the brown cam.

Looking a little closer at the same picture shows you more clearly what is going on. I’ve basically combined the cam follower which tracks along the brown cam at the bottom of the picture with a bell crank which will drive the pull strip (red), pulling the second bell crank in the knee. Now that the design is worked out I can give the paper version a try.