Step 2 - The Barrel
The barrel is made out of a 2 1/2" SCH 40 steel pipe that is 63 inches long and that encloses approximately 300 cubic inches.
This was threaded on one end and attached to one end of a 2 1/2 " steel union pictured below.
(Most threads were successfully sealed using teflon tape. Any remaining leaks were sealed using epoxy)
Step 3 - The Combustion Chamber
The combustion chamber was made out of 5 pieces:
- A 34 inch long piece of 4 inch, SCH 40 steel pipe which was threaded on both ends.
- One 4 inch pipe cap
- A 4 inch to 2 1/2 inch pipe reducer
- A 2 1/2 inch steel nipple
- The other half of the union
It is essential that the chamber is sealed and able to be pressurized within a range of 60 to 100 PSI.
Note : During hybrid combustion, the steel pipes will be experiences pressures in excess of 300 PSI. This poses a possible danger to the operator which is addressed in step 13.
Step 4 - The Metering System
The purpose of the metering system is to inject the correct ratio of fuel to oxidizer into the combustion chamber. The simplest way to do this is to pressurize the gases inside of a pipe of a known volume and then inject them into the chamber.
Note : Step 12 will explain how to operate the metering system
The metering system is perhaps the most complicated part of the cannon, and it will require quite of bit of work to get it working perfectly.
When using threaded parts, it is useful to know that there are many different classifications of thread types. There are compression threads (FIP) and standard pipe threads (MIP). This design of a meter uses both, and so it will switch between the two once or twice. This is just my particular design, so if you can think of something better, go for it.
The parts list is as follows:
- A 4 inch to 3/4 inch brass saddle
- 3/4" 90 degree elbow
- 3/4" 2 inch nipple
- 3/4" Ball valves (2)
- 3/4" 24 inch pipe threaded on both ends
- 3/4" brass nipple
- 3/4" to 1/2" Pipe reducing coupling
- 1/2" brass nipple
- 1/2" to 1/4" Pipe reducing coupling
- 1/4" brass nipple (3)
- 1/4" brass tee (2)
- 1/4" Pressure gauge (MIP)
- 1/4" Schrader valve (FIP)
- 1/4" FIP to MIP adapter (to connect the Schrader to the brass tee)
- 1/4" Pressure regulator with gauge
- 1/4" Compression connector with MIP adapter (to attach the end of the meter to the vinyl hose)
- 5 foot 1/4" vinyl tube
- 1/4" Compression connector (to attach to end of torch head)
- Propane pencil torch head
The regulator isn't absolutely necessary since the torch head already does regulates the flow, but it is handy and allows for more a precise measurement.
Step 5 - The Ignition System
Multiple ignition sources:
The simplest way to create multiple sparks inside the chamber is to use a high voltage source such as the one found in a stun gun.
The stun gun is connected to two spark plugs, which are practical since they are already insulated. The spark plugs are screwed and epoxied into two holes which I had to drill and tap into the chamber.
Drill the holes for the spark plugs using a 7/16 bit and tap the holes using a 1/2 inch, course thread tap.
Next, connect a wire from one electrode of the stun gun to the outside of one of the spark plugs. Then wire the two spark plugs together on the inside of the chamber. Lastly, wire the outside of the second spark plug to the second electrode of the stun gun.
When the stun gun is activated, there should be two large sparks inside of the chamber.
I just taped all the wires and the stun gun to the outside of the chamber for now, but I do plan on making a m
Step 6 - Final Construction of the Cannon
Since all of the parts are threaded, you can screw them all together using either teflon tape or a yellow gas line tape as a sealant.
Once all the parts are screwed together (except the end cap), you will need to connect the metering system to the combustion chamber via the brass saddle. To do this you will need to drill a 3/4 inch hole where you want to connect the saddle. Then epoxy and tighten the saddle around the hole using a liquid gasket silicon to seal around the hole.
A wooden block is recommended to support the other end of the meter.
Next you will have to drill and tap two holes for the spark plugs. Drill the holes using a 7/16 inch bit and tap using a 1/2 inch, course thread tap. Then epoxy and screw the spark plugs in.
Wire the two spark plugs together on the inside and to the stun gun on the outside.
Now, once everything on the inside of the chamber is taken care of, you can screw the end cap on.
When the whole cannon is constructed, you can check for leaks by pressurizing the system and spraying some sort of cleaner on all of the joints. If a part is leaking, bubbles should start to form.
A burst disk can be between the two halves of the union to seal of the chamber. The easiest and cheapest way to make a burst disk is to just fold a sheet of tin foil into 8-10 layers.