Justin's Electromagetic Impulse Catapult

aka Gauss Cannon

1st SISG Triggered Coil Gun


Gauss Cannon

Here is Justin's Coil Gun. It was built as a science project for school and thus "officially" titled "Electomagetic Impulse Catapult" in order to pass the vetting process. It fires 7/16" diameter steel balls through a 1/2" ID clear acrylic thin-walled barrel. When charged to 900 Volts it fires over 30 feet. Current is ~180 amps and the bang is 178 Joules!! We built this over the Christmas Holidays of 2008. It is the first SISG fired device of its type

Basic Construction

Here one can see the internal construction of the impulse circuit. On the left is the 433 uF capacitor bank attached to a homemade PC board. On the far right is the 12 volt battery (blue) to power the power supply circuit. Above the battery is the MOSFET driver board to pulse the flyback. In the center section of the box is the flyback on the right and the SISG circuit board on the left. The SISG circuit is slightly modified from the one we use for Tesla Coil service becasue of the low resonant frequency of the Gauss Cannon circuit.


Capacitor Bank

The Capacitor Bank is shown here. It is (9) 3900 uF /400 Volts Electrolytic Caps wired in series for a total capacitance of 433 uF and a voltage rating of 3600 volts. Because this is a pulse discharge type system, the capacitors should not be electrolytic. We chose them because we had them around and this is a temporary project not designed for repeated operation.

Flyback Transformer

Here is the Flyback Transformer. It was made from the ferrite and coil forms from an old flyback. The secondary has about 1000 turns and the primary 42 turns



On the left is the MOSFET Power Supply. It uses a 555 timer to drive a pair of transistors which in turn fire the FET and drive the Flyback Primary. The Power supply is 12 vdc from a battery. It takes about 110 seconds to charge the capacitors to 900 volts.

SISG Trigger

The Sidac IGBT Spark Gap is used to fire the cannon. Three 300 volt Sidacs wired in series trigger an IGBT when their voltage threshold (3X300 = 900 volts) is reached. The circuit was modified from the Tesla Coil service SISG in that the gate shutdown resistor was changed to 100K ohm because the resonant frequency of the coil gun is only 215 hz whereas our SISG TC is 168K Hz!! In addition, a 4.9K ohm rsistor was mounted in paralled with the TVS to prevent the leakage current thru the Sida balancing resistors from triggering the SISG prematurely. Currently, we are using only one SISG circuit on the board. Note there are two circuits (see the 2 heat sinks for the IGBT's) mounted so that in the future we can try higher voltages.


Barrel Construction

The clear acrylic barrel is mounted inside a 1/2" PVC pipe for stiffness and the pvc cross allows the barrel to pivot. The 6 layer 300 turn coil is embedded in epoxy on a brown paper and epoxy coil form designed to slip over the acrylic tube. The breech can be observed on the left. The wooden stick simply holds the ball in place in the breech for firing. The position of the ball with respect to the coil makes a huge difference in the range. The meter is connected to a voltage divider so that we can observe the charging of the caps. A wooden stick below the meter has a copper electrode to short the caps thru a resistor when not in use to insure the cap remains discharged.

Click Here for Coil Gun Schematic

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