I have wasted so much time on these things, after discussions about pendulums I took another stab at making a wave pendulum. The idea was straight forward, use a knife edge to balance the pendulum. This solved several problems, it's a simple design with no calibration required and the supporting beam could be an angled metal bar which would take all the weight of the pendulums. The knife edge was created by sanding down a piece of 0.8mm ply and initial tests were very promising.
I made the shortest pendulum first to see if it would swing for long enough, the system needs 1 minute for a cycle and the pendulum swang for 3 minutes. I ploughed on and made the rest of the set. When they were all pulled back though there was an element of wangle on some of them. This produced uneven swing and the cycle was broken before it even got going. Experiment 3 was a write off and there ends my efforts. If you want to make a wave pendulum system, using string and measure it out to the right lengths.