If you have ever tried to ignite rocket motors, you probably go frustrated to no end, I know I did. I tried a bunch of D-cells, 9 Volt cells etc. Ignition was hit or miss using these systems. There is nothing more frustrating than no ignition when the red button is pressed!!! So I decided to take the over kill approach. I wanted to use a motorcycle battery, however I also wanted to switch high currents from at least 100 feet away. The result is a circuit that is proven to work very well.

This is the system diagram. Basically, power is routed from the battery to the relay unit. There it is switched by relay that is activated by switches in the control unit. Once the relay is activated, high current is applied to the ignitor of the rocket motors. I have successfully ignited 5 motors simultaneously with this system.

The control unit receives power from the battery. The ARM switch should be a toggle SPST type switch. Once activated, The RED LED will light. Now the circuit is ready to activate the relay. The FIRE switch should be a "momentary" SPST switch. This switch springs back automatically when you let it go. Once the FIRE switch is depressed, the relay coil is energized and closes contacts RY1-A. By closing RY1-A, battery power is applied to the rocket motor ignitors. NOTE: I used a 5-6 VDC relay in a 12 volt circuit. The reasons for this are:

• The battery being used may be below 12 volts, hence a 12 Volt relay won't energize.
• If the wire length to the control unit is very long, there may be a volt or two drop across this wire, so a 12 Volt relay won't energize.
• Momentarily applying 12 volts will not damage the 6 volt relay.

NOTE: The wire between the Relay Unit and the rocket motors should be at least 5 feet long. The motor exhaust gases will corrode the alligator clips & wire and you will have to cut them back or replace them after several launches.

Here are some pictures to see how simple this project is.

Control Unit

Relay Unit