I added a second cam and connecting rod to my arm yesterday. It definitely solved the twisting problem. In the long run, I’d rather just have a single cam, because adding the mechanism to adjust the offset from the cam will be twice as difficult with 2 cams. For now, twin cams, fixed connecting rod length.
The most obvious problem right now is that as the cam switches from pushing UPwards on the connecting rod, to pushing DOWNwards on the connecting rod, the whole assembly clicks and jumps a bit.
I’m also getting way too much friction in all the little rods and bearing surfaces, part from the design, and part from my lack of holding tight tolerances in the machining process. This friction is so great that the arm is sluggish, and I doubt would do much stabilizing in use.