The cannon has three coil stages that accelerate the projectile one after the other. First, the coil is off and the projectile isn't moving. But then we turn on the coil, current starts to flow through the coil and the bullet starts to move because the magnetic field of the coil is accelerating it.

Then, when the projectile is in the middle of the coil and the kinetic energy is at its maximum, we have to turn off the coil. Because if we keep it on, it will slow down the projectile and will oscillate back and forth. We can detect when it has reached the center using a CNY70(infrared sensor).

And now, the projectile will exit the coil stage with a good amount of velocity and it's ready to go out of the cannon or to be accelerated again by the next coil stage.

Here is a shot of the firing process in an oscilloscope. As you can see, current is first applied to the coil, then the CNY70 detects the projectile and the coil turns off.

• GATE = Gate of the MOSFET.
• IL = Voltage through the coil.
• A_IR = Analog output of the CNY70 sensor.
• D_IR = Digital output of the CNY70.

And this is the final result of the coil gun: