Anyone
who has played Age of Empires (this includes me, yes),
will know exactly what a trebuchet is, and what it does.
A trebuchet exists as a medieval rock throwing machine,
but quite different to a catapult.
Here
is an oversimplified diagram of an armed trebuchet.
CW stands for counterweight, and the release pin...
well nevermind you will see what that's for later. Don't
you love it when I explain things?
Gravity
pulls the heavy counterweight down towards the ground.
Because the counterweight is attached to the throwing
arm on one side of the axle, the projectile side of
the throwing arm is pulled upwards. The rate of movement
on the right hand side is faster than the left hand
side, due to the lever physics.
The sling
carrying the projectile is carried forwards by the lifting
arm.
As
the counterweight falls some more, the sling is brought
off the ground by the throwing arm, and travels at a
tangent to the circle traced out by the throwing arm
(at any instant).
The throwing
arm is now nearing perpendicularity with the ground.
However, the release pin is angled differently, and
the loose release string on the sling is starting to
slip off the pin. Note that the projectile is held tightly
by the sling so that it can't just fall out.
At
a critical angle, the release string is well... released
from the release pin. The momentum of the throwing arm
makes sure that the released string lifts up high and
wide of the projectile. The projectile is thus released
from the pouch, and follows a tangential path at that
instant.
Momentum
carries the throwing arm through, and everything swings
and sways and does whatever it has to do before collapsing
into its unarmed state.
The
Penguin's Lab Trebuchet!
This
was the result of a rushed project using materials in
the near vicinity (the shed), and materials were definitely
limited, so please spare my ugly construction methods.
The
trebuchet originally consisted of one microwave oven
transformer as a counterweight (trust me, I have alot
of these). This, however, was increased to two microwave
oven trasformers after it was decided that the range
was not adquate. The counterweight now measures in at
around 15kg.
A view
of the 2 MOT (microwave oven transformer) counterweight.
I had previously attempted to secure these to the throwing
arm using rope, but the rope snapped on the first go.
When the
trebuchet is fired, you can hear the fatigue in the
metal fastenings. But who cares, it works!
The
triggering pin is shown here. Two curtain hooks attached
to the end of the base serve as the holders, while a
camping peg is the triggering pin. The string attached
to the peg is pulled to fire the trebuchet.
A closer
view of the axle. Aluminium tubing is passed over a
decking spike (which serves as the axle) to reduce frictional
losses between wood and metal. The two wood pieces bound
to the throwing arm are reinforcement pieces in case
the throwing arm snaps at the axle (which is unlikely,
but with such a heavy counterweight, you never really
know).
The throwing
arm was configured for a 4:1 ratio between sling side
and counterweight side respectively.
A
stroboscopic shot of the trebuchet firing a blank shot.
From here you can see the maximum deviation of the throwing
arm on the left side. Unfortunately, the strobe light
was unable to capture the pouch releasing from the release
pin.
The
current maximum range of the trebuchet for a 50 gram
projectile has been recorded as ~15m.
Here is
the trebuchet in action (slow motion).
Some
lightweight statistics- the trebuchet has:
Bent
one axle (made of solid steel), and competely destroyed
another (made of copper)
Had
its support frame modified many times due to massive
amounts of stress on screw joints, which caused
splitting of wood.
Had
three different counterweights attached; 1 MOT,
2 MOTs, and 2.5 MOTs (which is in use now).
Tipped
itself over a million times after the heavier counterweight
was attached, even with three heavier transformers
securing the base to the ground. (I told you I had
alot of transformers).
