Gray Shot Ignition Powder

As my rocket motors have become larger, I've run into a minor problem. The increased distance between the launch controller and the launch pad has meant longer wires, which means more resistance and less current to the Igniter, which in turn causes the igniter resistance wire to heat up more slowly, resulting in a delayed ignition. Not that it's the end of the world having to hold the button down for a few seconds, but it is nice to see the rocket lift off quickly once you say ignition.

There are numerous ways I could resolve the problem.

• I could have gone to 24 volts instead of 12, but that means carrying around another battery, I don't think so.
• I could rebuild my launch controller with a relay and a battery closer to the pad. That would be a lot of extra work, and expense.
• I could go with heavier wire from the controller to the pad. But that gets expensive and heavy.
• I could buy some real nichrome wire that heats up with less current, but that would be too easy!
• I could use x-mas tree bulbs with a new ignition powder. They fire on very low current.

Of course, I opted to go with the x-mas tree bulbs. The real reason I went that way was because I wanted an igniter I could use with my 555 timer to light the sustainer on a two stage rocket. So I could kill two birds with one stone.

What I wanted from the ignition powder was a relatively slow burn with lots of hot sparks. I tried several things, plain black powder was the first. I used some home made black powder because I knew it burned slower than commercial black powder. It would have worked, but it was a little faster burning than I wanted. I then tried a mix of 10 grams KNO3 and 5 grams sugar. It burned too slowly. So I added 5 grams of home made black powder to get it burning a little better. That did the trick, now I wanted more hot sparks. So I added 1 gram of Magnesium flour and mixed it for several minutes in a paper cup. When completely mixed it had a nice gray iron color, thus the first part of its name.

I didn't want the powder to burn too quickly, I don't like the idea of setting off an explosive charge in the motor, I'm just a little afraid of cracking a propellant grain if it pressurizes the motor too quickly. I used the soda straw like I do for my deployment charges, only instead of sealing the end with hot glue, I used a small wad of paper towel to hold the powder in the straw segment. If I tried sealing the end of the straw, I got a pop and that was all. About like a good sized fire cracker going off. With just the paper towel wad, the igniter would go off and shoot a small stream of fire and sparks out the end of the straw. Sort of like a little cannon shooting, thus, the second part of the name "shot".

Here are the completed igniters.

Here is one I fired as a test. Notice the intact straw.

Here's a summary:

Mix 10 grams powdered KNO3, 5 grams powdered sugar, 5 grams powdered home made black powder, and 1 gram of flour sized Mg powder. Mix it all together for several minutes. Use a non metalic container and a wood or plastic mixing device. Cut regular size soda straws to 1 3/4" in length. Hot glue the soda straws on to a x-mas tree bulb (the very little ones) that have had the tip of the bulb broken off (I touch them to a grinding wheel). Fill the straw to within 1/4 inch off full, then wad up a small ball of paper towel and insert into the open end of the straw to keep the powder in the straw. Be careful, too much wadding, or compressing the powder may cause the igniter to pop rather than shoot. Finish by twisting the wire ends together for safety, and store in a sealed plastic bag in a safe place. I like to date and label each igniter as they are made so there is never any doubt as to what it is.

The downside is these igniters are fairly large, as such, will only work in motors with large nozzles. But that's ok, as I only need these igniters for large motors anyway.