This guy is a nutcase 
but i like his creation.. a CD Launcher that launches a CD at high
speed
Hammerhead the CD thrower is composed of two main parts, the head
that throws disks, and the tail which feeds the head with compact
disks.
The
Head
Two big "4x4 off-roader" (8466)
wheels, rotating very fast, grip the CD as it is inserted between
them by the feeder, and eject it on the other side. This mechanism
is inspired by the LEGO disk thrower described in Ultimate Builders Set
(3800), but much more powerful.
One of the wheels is powered by a single "Motor movers" motor, a
powerful unit with medium rotation speed.
The other wheel turns much faster, as it is driven by two old 9V
motors. Without down gearing, these motors can be easily stalled,
but thanks to the mechanical energy stored in the heavy, fast
rotating wheel, the slowdown as the CD passes between the wheels is
barely noticeable.
The benefit of two different wheel speeds is that the CD spins on
itself after launch. This rotation stabilizes the disk
flight.
Evaluation of disk ejection speed:
Rotation speed of slow wheel is 420 rpm, while fast one is 1800
rpm. As wheel diameter is 10cm and CD diameter is 12cm, we can
derive disk ejection speed: 5.8 m/s (21 km/h or 13 mph) and spin
speed: 1150 rpm.
Motor power is provided by two RCX outputs. As old 9V motors draw
high current at startup while building up wheels speed, they are
driven from separate RCX outputs. The other wheel motor, thanks to
its internal down-gearing, consumes less power and share a RCX
output with one of the old type motors. I used an old RCX 1.0 unit
powered from mains, because the internal voltage is a bit higher
than 9V and the motors turn slightly faster. I originally intended
to use an external battery pack to power wheels motors, berhaps
boosting voltage using 3V lithium cell to get even higher rotating
speed... but finally I found that Hammerhead was scary
enough!!!
The
Tail
A carriage moves back and forth, guided by two side rails. Two lugs
(orange) grip one disk at a time and push it between the wheels
where it is caught and thrown.
The two axles placed above the rails let only one disk to pass
through.
A motor (connected to the third RCX output) moves the carriage
using the gear rack placed underneath
Two bumps activate a touch sensor when the carriage motion needs to
be reversed.
A light sensor places above the CD stack checks when the magazine
is empty and stops Hammerhead.
But.. you have to see it in action:
click here => Clip 1 from top
view
and here => Clip 2 from rear
view
(source: Philo's Home
Page)