To accurately and repeatedly shoot a tennis or golf ball at camera we built
an air cannon with a barrel to just fit each ball. A 1 foot diameter low pressure
air tank was filled with air at a specific pressure from a high pressure tank
and released by an 1-inch IPS electric solenoid valve. The pressure in the air
low pressure tank could adjust the trajectory of the ball. The air tank sat
in a square box that allowed adjusting the barrel angle. Whatever adjustment
method you use make sure it can't change between shots. There is a little kick
to the firing. Of course do a lot of testing before the shoot. Any shape tank
will do that will handle the pressure.
A pressure regulator on the high pressure air tank kept the pressure constant
for each shot. The whole content of the accumulator dumped each shot. For a
higher or lower trajectory we changed the angle or pressure or both. To load
tennis balls with the label to camera we made a ramrod with a half ball on the
end that kept the ball in the same position as the ball was loaded. The barrel
was just a bit smaller than the ball.
We included a tennis player following through his stroke in our tennis shots
and hid the accumulator rig behind a slightly wider top band on the tennis net.
We focused an Arri straight mount 75-mm lens with a motor that slid the lens
out of the mount as the ball approached camera. Both the solenoid valve and
focus motor were tripped at the same time.
For golf balls we hid the accumulator rig slightly over the horizon and framed
the golfer behind the rig following through his stroke. In both cases we were
comparing the supposed better qualities of the balls we were promoting. The
competition, of course, did not appear fly as far.
Projectiles of many kinds can accurately shot with the right barrel.
© Copyright 1999-2004 Ron Dexter. All Rights Reserved.