The idea behind the chain we built. Other ideas for chains that pull-in are in the paper.

If one lets a tilted rod fall onto a table, its other end speeds up on hitting (by 50% for a uniform rod with small θ having plastic impact: V B+ = 3V/2).

(That's why things break on the 2nd bounce, see the cover story in the Wall Street Journal, Friday Dec 17, 1993).









Now if we attach something to the end B of rod, that will speed up after A hits. This is the basic idea we use for our chain. We make a chain whose links are tilted rods arranged in a zig-zag pattern vertically. As each link hits at one end its other end pulls down on the chain above.



Devices



Chain: we made the chain with tilted rods as its links.

Release mechanism that drops the chain simulaneously.

High speed camera. Phantom V7.1 camera at 2000 fps.





Making the Chain

We used two essentially identical chains made of dowels tied together with Vectran. The weights of the two chains were 218g (plus or minus 2 g).













Trigger-Release Mechanism

Originally an electromegnetic release was used. It didn't work well. The magnetic field stayed on briefly even after turning off the current, and this was hard to control between the two magnets.Finally a mechanical release was devised and built as shown below: