Credit to my buddy Ed Galore.
Check this out:
Make your own. Form the comments:
Materials don’t matter, but you have to make it so you are able to adjust the lengths of each pendulum precisely. Our longest pendulum completes 51 swings in one minute. The next one 52 swings in one minute. Etc etc. The 15th one 65 swings in one minute. You can choose any numbers (and time) you wish. The important thing is that they all have executed an integral number of swings in whatever time you decide. That’s when they come together again and start the cycle over.