Double Voice Cracker
From PyroGuide
Tutorial under construction
A double voice cracker is basically a firecracker that pops once on the ground, and then again in the air. It is more or less a self-contained aerial salute.
Materials
Casing
A thick paper tube is used as a casing. About 5/8" ID thick walled tube should be used. Under no circumstances be tempted to use materials other than paper. It is dangerous and unnecessary. Find, roll or buy thick walled cardboard tubes, preferably parallel wound as they are much stronger than spiral wound tubes. The tubes should be sufficiently strong to allow the initial explosion to propel the device upwards, without bursting the tube apart. A wide range of casings can be purchased from Wal-mart and Pyrocreations.
Tools
A rammer and mallet are needed. Non sparking materials, such as aluminum, brass, rubber and wood should be used. You will also need paper tape and a scoop for your various powders. A hole punch is also helpful.
Propellant/Report composition
Lifting Charge will do for the propellant. Flash powder, Black powder, or similar report compositions can be used for the report.
Internal plug
Bentonite and kaolin clay work well. The dry clay powder is rammed into the middle of the casing, producing a solid plug. Cheap kitty litter is often made of bentonite clay and may be used instead. Grind up the kitty litter into a fine powder, which is most easily done with a ball mill or coffee grinder
Delay Fuse
Fast and slow visco are sufficient for timing.
Tutorial(needs more work)
To make a double voice cracker you are going to want to first put a bentonite plug at the bottom of the casing you are using. Any casing is fine, as long as it is thick enough to withstand the lift charge. After that you have to drill a hole just above the plug to make a fuse hole. Next you must now put in your lift charge. Fill the tube at least 1/4 of the way so that you may put another bentonite plug on top of that lift charge. That plug should take up 2/4 of the casing. That plug is going to be in the middle of the casing. After that get a suitable drill bit and drill a hose down the clay into the lift charge for the fuse. Once that hole has been driven in cut a piece of visco or fast fuse to the length of the clay plug but just a mm longer. Now you have to split the fuse at the bottom, so basically just cut a little vertical slit at the bottom of the fuse. That will be there so that the fuse can catch the fire more easily. After you have done that insert the fuse. Next you are going to want to fill the casing above the fuse with a payload of your choice, only fill it up until you have a little more space for another clay plug. I prefer flash powder. After you have paced your payload in either close it off with standard tape used for packaging or with a bentonite plug.