Page 41 - 15 Dangerously Mad Projects for the Evil Genius

22 15 Dangerously Mad Projects for the Evil Genius

You will likely need to make a few adjustments
to the pin before this works well. If the ball flies
off too low to the ground, then bend the pin back a
little so the sling is released earlier. Or, if the ball
is released too early and flies straight up into the
air, bend the pin forward a little.
This book’s web site (www.dangerouslymad
.com) contains links to videos showing the
trebuchet in action. These may be useful to
refer to.

Figure 2-14 The trigger mechanism
Theory
(Figure 2-14). To fire the trebuchet, simply pull the
The trebuchet takes its energy from the weight that
nail out.
falls as the arm swings. This “potential” energy is
transferred to the arm and sling of the trebuchet
Fire! and is released as kinetic energy in the tennis ball.
As we know the energy stored in the weight and
A tennis ball makes a good projectile. It has the know how far the tennis ball can be thrown, we
advantage of being fairly tough and not being can calculate both the energy going into the system
damaged by a collision with a target (minion). To and the energy released into the ball by the system.
test the trebuchet, a suitable open space should be This will allow us to calculate the efficiency of our
found and minions dispatched to a reasonable trebuchet.
distance in front of the trebuchet.
The input energy can be calculated using the
Fit the ball into the sling and pull down the formula:
throwing arm until it can be pinned by the trigger
E mgh
nail. Stretch out the sling in the runway, with the
ball at the far end, so that the rope is straight and where m is the mass of the weight, g is the
the loop is over the pin on the end of the throwing gravitational acceleration on Earth (9.8), and h is
arm. the height.
Stand clear of the trebuchet and pull on the So the energy in joules is approximately:
string to release the nail holding the throwing arm E 8 kg * 9.8 * 0.5m
in place. The ball should sail off into the distance.
40 joules
Dispatch a minion to retrieve it and do it again,
On the other hand, we can calculate the
because it’s fun.
approximate amount of energy that was transferred
into the ball on the basis of the distance that it
Tuning the Trebuchet traveled and its weight.
1
E mv 2
There are various things you can do to the
2
trebuchet to squeeze the best performance out of 2
d v v dg
2
the engine. g