Page 50 - 15 Dangerously Mad Projects for the Evil Genius

Chapter 3 ■ Ping-Pong Ball Minigun 31

Figure 3-10 The magazine attached to the leaf blower

Testing As a target for measuring the speed of the balls,
a wall, window, or other solid object is much better
It is now time to try out the gun.
than a minion. Minions are soft, and while they do
The gun should be used indoors, or you are make a noise when hit by a ball, a considerable
likely to lose the ping-pong balls. Once again, a delay occurs as the message slowly propagates
minion is required as a target. Stand at least five through their nervous system and eventually
yards (meters) away from the minion. After giving reaches their brain. This delay tends to spoil the
them strict orders not to step on any of the ping- accuracy of the figures.
pong balls, fire up the leaf blower and tip in a few
Your laptop should be positioned close to the
balls to get your aim right. Once your aim is
target rather than the leaf blower to reduce the
accurate, pour in the rest of the balls as quickly as
extraneous noise created by the leaf blower.
possible.
The leaf blower is very noisy, so it is much
harder to tell from our sound trace exactly where
Finding the Muzzle Velocity
the ball left the nozzle of the gun. A trace is shown
We can measure our muzzle velocity using the in Figure 3-12. The range between when the ball
same approach we did with the coil gun (see leaves the gun and when it hits the test target is
Chapter 1). We will only need a single ping-pong marked on the diagram. The only way to determine
ball and the impact target must be placed much the moment the ball leaves the gun is to repeatedly
further away. The arrangement we used is shown play part of the sound wave. Your built-in signal
in Figure 3-11. processor (brain) will be able to separate the “pop”