Hello Steve, I was wondering if you are familiar with a wooden clock designed by DickB called Synchonicity? Specifically, I am interested in the method of speed regulation by altering the pendulum swing amplitude. I have been tossing around doing something similar with your electo-magnetic pendulum design. With my lack of mechanical engineering and coding skills it might be difficult for me to pull off. But I'm sure I would learn something while trying even if I failed. I'm betting you are familiar with it but here is a link to an instructable just in case.
Anyways I was just wondering if you had ever considered something along these lines to increase the accuracy of your electro-magnetic pendulum clock?