How Does the Coil Gun Work?





The coil gun consists of 3 main parts; the camera charging circuit, the voltage reading circuit, and the cannon/firing mechanism. The camera flash circuit involves an oscillator that pulses voltage through a small transformer found on the PCB. The transformer (a fly back variety ), feeds the stepped-up voltage into a large capacitor (usually a 300V, 470uF). When the camera is triggered to generate a bright flash of light a second transformer (which is also connected to the capacitor), creates a voltage pulse that is even bigger than the large voltage stored in the capacitor. This large voltage pulse is then fed into a wire that sits behind the flash tube and this causes the gas inside the flash tube to become conductive. Since the flash tube is connected across the capacitor in parallel , the capacitor discharges through the tube and generates a bright light. In our circuit, however, we do not need the flash tube and so this is removed from the PCB along with the trigger connectors and the charging switch.

The charging pads (found on the PCB), are instead, connected to an external tactile switch that makes charging the capacitor much easier. The positive lead of the capacitor is connected to a small copper pad that sits at the contact point of our firing switch. The other side of the firing switch is then connected to the top side of the coil. The second coil lead is then connected back to the capacitor on the camera creating a pulsed electromagnet. When a projectile is loaded at the base of the coil gun tube and the system is fired, a short-lived but powerful electromagnetic field is generated which attracts the project (which must be ferromagnetic), and throws it out of the end of the other tube.

This coilgun setup also has a three-digit voltage meter which is connected to the capacitor via a potential divider made up of a 100K resistor and a 1Meg resistor. The potential divider creates a voltage that is approximately 1/10th of the voltage across the capacitor (such that 100V would correspond to 10V), and this allows for the voltage meter to take readings without breaking. The large value of the resistors also prevents discharge that otherwise could be a problem for firing. The coin cell is used here to provide a separate power source for the voltage meter. The voltage meter here requires at least 3V and the camera is powered from 1.5V. If a 3V power supply is provided for both the camera and the voltmeter then the camera does not operate properly (as it is reliant on 1.5V), however, this depends on the camera being used. Some cameras can operate on larger voltages and when they can, they usually charge very quickly.