The control box provides five high value capacitors which can be switched into the charge circuit as required. 
This highly original apparatus offers an exciting application of topics such as energy storage, capacitor charging, mechanical energy, efficiency and electromagnetism. 
When the FIRE button is pressed the energy stored is released as a pulse into a low resistance coil to fire a small steel projectile. 
Mass 0.5kg
Variables include, voltage, time, capacity, distance, kinetic and potential energy. 
Dimensions 220 x 110 x 80mm excluding coil