Despite appearances (given the length of time since my inaugural post), this project is steadily, if slowing, progressing! One major reason for the delay has been my starting a new job with a robotics startup, which has consumed a lot of the creative energy that was going into this project (a good thing). But being in that environment has also meant I'm surrounded by people who are experts on various aspects of this project, so I can grill them for suggestions.

Anyway, I'm currently designing the physical hardware for the pendulum test rig itself. There are several elements to this which I'll talk about as I resolve the design, but in this post I wanted to highlight one small aspect I've settled on. 

The pendulums will consist of 12mm diameter, 1mm thick (i.e. 10mm ID) aluminium tubing, cut to length.  I anticipate that I'll probably want to be able to swap out different pendulum lengths as I work on the controller, so I want something that easily clamps on to the tubing and can be detached when necessary, and this is what I've come up with:

White piece is SLS Nylon. A threaded insert goes in the top, and an M3 grub screw is screwed in - as this is tightened it forces the tips open against the walls of the tubs it's inserted into.

This shows how an M3 screw attaches the plug/tube assembly to the axle:

Next, more design, and controller electronics choices!