|Black Powder Igniters|
|Note: Pictures (very helpful) coming soon!|
Although simple, black powder igniters are very reliable. If made with patience, they have a high success rate, and will ignite motors very well. This tutorial will explain the construction of two different types of black powder igniters.
The first is for smaller motors, I use them for ĎE classí and below. They consist of a steel wool heating element, and black powder with a lacquer thinner binder. Two wires are twisted together, to a length of the experimentalistís judgment. The ends of both wires should be stripped, to the length of about .5-.25 cm. (longer than this range is better than shorter). These wires should end up being long enough to reach the top of the propellant grain core, and stick out of the nozzle enough to be easy to use (however long youíre used to your igniters sticking out). I usually have mine stick out of the nozzle about an inch, but this gets bigger with bigger motors. We will now be working with the igniter end of the wires. Make sure that one of the wires is shorter than the other. The optimum difference in lengths here is the length of the propellant grainís core. Twist a filament of steel wool together. It should consist of 5-10 strands twisted together, just estimate. Attach one end to the shorter wire, and the other end is attached to the longer one. I make it twist around the wires once for a little extra strength. A trick that will add a lot of strength to the filament is after you have twisted the strands into a filament, spray them with Crystal Clear Acrylic CoatingÖ probably any aerosol acrylic coating will work, but this is the only one Iíve used. This should be done before attaching the filament to the wires. If many strands break while you are attaching the filament to the wires, or at any other time, you should discard it and make another one; otherwise, your chances are high of having a dud igniter. Once the filament is attached successfully, dip it in lacquer thinner, then in black powder. Some of the black powder will fall off, but thatís ok. Just be gentle. Let it dry, forming a coat of black powder on the filament. Then, dip in the black powder once more, dry. Be very gentle with it. Once itís in the motor, you shouldnít have to be so gentle. I use a 220microfarad capacitor, which charges to 330 volts, to fire this igniter. If you open a disposable camera with a flash, remove the IC board, and use this for the power supply to your igniter (see ignition system). If this is all done right, the igniter should fire with very good success every time. It will take a while to get used to.
Igniters of larger motors are very similar. They are made of one of the above igniters, a soda straw, and black powder. First, obtain or make one of the above igniters (other igniters will probably work fine). Place this in the straw, and seal one end with hot glue. The end that should be sealed is the end with the wires coming out. Now, fill the straw with black powder. Tap the side of the straw so that the black powder settles, but donít pack it any harder than that. Continue this process until the straw is full, except for about 1 or 2 millimeters of space at the top. Seal the top in this space with hot glue. Now, test for currency with a voltmeter (if you donít have one, just work very carefully to make sure not to damage the filament.) Before loading these igniters into a rocket, I always give them a good shaking/tapping right side up so that the black powder in the straw will really settle around the filament. I have had igniter failures without this shaking, but after I started shaking them, I have had a 100% ignition rate. When you shake, though, make sure that the igniter leads are at the bottom, not the top. If theyíre at the top, then you are settling the black powder away from the filament. If made correctly, these igniters are very reliable. As a final note on size of the straw, pick a straw that is as wide as will fit into the motor, and cut it to about1/3 the length of the propellant core. Also, make sure that when the igniter is loaded, it is all the way at the top of the grain, opposite the nozzle, rather than the bottom. This causes the sparks from the igniter to be pushed down along the core, and ignites the core all at once- a much more efficient burn of propellant. A test was conducted, using the same motor, and when the igniter was loaded at the top of the grain, the motor got a very powerful burn for 2 seconds, but when loaded at the bottom toward the nozzle, there was a very weak burn for about 10 sec. Black powder igniters are probably the least dangerous pyrotechnic device you will find on this page, but as always, use extreme caution, and donít try these things unless you are very experienced in the field.