In my early sugar motor experiments I was using fuses to light the propellant grains. This resulted in the motors burning from the bottom of the core to the top, which had a few significant effects on the burn rate, internal pressures, etc. It just wasn’t good. In keeping with the rest of my goals for this project, I looked into making my own electric matches, pyrotechnic triggers that would get hot enough to ignite the propellant.
I know there are commercially available options for this out there. But here’s what I’ve found.
With my launch controller setup (providing 12v @ 2 amps with a 6ohm burden in line with the igniter) I’ve measured that 50mm of 40 gauge nichrome wire glows quite nicely (and quickly) without burning through with a 1 second pulse. However, it seems to not get hot enough to ignite pure sugar fuel in a fast manner. So I think it’ll be best if I mix black powder into the sugar fuel, then use that to pack around the igniters.
As for the nichrome, when wrapping that around a 1mm wire removed from a bundle of cat5, it takes about 16 wraps to get the 50mm. If you want the igniter to get hotter faster, you’ll reduce that number.
The issue I’ve been having, is that the insulation melts and shortens the conductive length of the nichrome, which then means my burden resistors get a bit too much wattage through them and start to smoke.
If I ever build another one of these stands, I’ll have to be more careful with the heat dissipation capability of the burden resistors, and I’ll probably have to go to a wire-wrapped ceramic resistor for that.
But it looks like the theory is solid, and that this will work to ignite motors from the tip of the core, providing more initial thrust, hopefull a shorter burn time, and increased chamber pressure.
Only one way to find out, right?