Random Bits of Pyrotechnica - ceowyn Firing TBC

ceowyn Firing TBC

Anthony is firing my Tennis Ball Cannon for me for an experiment in the Armory back yard, as Mike Scott watches. The object was to try to get a picture of a tennis ball exiting the cannon.

The small white box stuck to the bottom front of the cannon (with Velcro) is a component from an ancient (1970s) alarm system. On the front of it is a normally-closed pushbutton switch poking through a metal plate. While a magnet is attached to the plate the pushbutton is pressed, opening the circuit. In an alarm system, the magnet would be attached to a tripwire, door, etc. I've screwed a bolt into a magnet and mounted it on this plate such that the bolt is in the path of the tennis ball. The bolt is attached to the box with a piece of elastic shock cord to restrain the bolt/magnet part. The cord dangling down from the box connects to the switch and is used to trigger a camera, which I'm holding and aiming.

Unsurprisingly, the camera mirror/shutter were nowhere near fast enough to catch the tennis ball, so all we get is this picture of the bolt/magnet flying away. The camera I was using didn't have mirror lock-up capability. I never got around to trying the same experiment at night with a strobe setup, which would certainly have been fast enough.

The camera trigger is described here.

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This image copyright © 1989 John H. DuBois III
This gallery created on Wednesday, May 26, 2004 • 1 of 12 images displayed