Special-Effects Consulting: implementing a theatrical gimmick

This article describes my contribution to a modest bit of stagecraft.
animation of relay
A simple illustration of the "effect"

In 2007 I had a call from the Tech Director at The Blyth Festival. One of their shows in the upcoming season required a special effect, and they wanted assistance.

The effect they wanted to achieve was very straight-forward. On stage throughout the play was a large, stylized tree made of papier-mâché and other materials. Two leaves were supposed to detach and fall off the tree, by remote control and according to individual cues. Of course the mechanism to achieve this had to be reliable and easily concealed.

Several different mechanisms could have done the job:

  • a spring loaded clamp (de)actuated by pulling a thread or by applying pressure via a thin, flexible air line
  • a thermoelectric clamp based on Flexinol actuator wire
  • an electromagnetic device — an electromagnet

We settled on the electromagnet approach. The idea we began with was that the leaf would contain a slender metal pin which would stick to the electromagnet, and of course the leaf would fall when the power was switched off. But the idea morphed unexpectedly while I was shopping for materials.

I bought a couple of electromechanical relays, intending simply to scavenge the coils and discard the other pieces. That would be easier than fabricating electromagnets by winding coils myself. But, as often happens, I got some new ideas once I was dealing with the materials hands-on. I realized that the relay could be used more or less intact, with the relay contacts functioning as an electrically controlled clamp.

In the final arrangement we didn't need metal pins in the leaves. Instead, each leaf had a short, slender paper tab glued to the back. The relay contacts were easily able to pinch the paper tab and support the minuscule weight of the leaf. The leaf would fall when the power was switched off and the spring loaded relay contacts opened. Blyth personnel took care of setting up the interconnecting wiring and a couple of switches offstage. The power supply was an ordinary AC adapter, the type commonly used for radios and other small electronic appliances.

The client got an effective and economical solution, thanks to my unconventional use of off-the-shelf materials.

Servicing the Unserviceable
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copyright notice (Jeff Laughton)