The first attempt
Choose a Pressure
- Poot (5-15 psi): Gently lobs objects, suitable for indoor use. It makes a sound which can only be described as "poot".
- Thud (20-35 psi): This setting would be very painful if fired at a person. It propels objects with enough force to damage things.
- Crack (40-60 psi): Not quite as dangerous as a real gun, this much pressure can still do a lot of damage. Objects make a distinct cracking sound when they hit at this velocity. 40psi was enough to put a hole in my garage door (oops). The gun also makes a crackling sound for a few seconds after firing; I'm not quite sure why yet.
If you build the gun well, you should also be able to try out the "BOOM" setting (70-120 psi). This can be dangerous. Make sure to test the gun's pressure tolerance with water first. (fill it with water, then put in more pressure than you intend to use; this is a fairly safe way to make sure it won't explode)
Pictures and Diagrams
As usual, click on the image for a bigger version.
How to build your own TTG Proto1
- A foot or so of 2" PVC pipe
- Two feet of 1/2" PVC pipe
- PVC size-adapter parts for 2" -> 1/2"
- A 2" pipe to inside thread connector
- PVC size-adapter parts for 2" -> 3/4", such that the largest piece has threads on the outside, and the small end has threads on the inside
- A very short 3/4" threaded PVC pipe (a.k.a. a "nipple")
- 3/4" Ball Valve, or... UPDATE! I've found that hose-squirting nozzles work quite well, too! (the kind which has a handle to squeeze) I'll try to get pictures soon...
- Screw-in air intake valve, similar to those on tires
- Bike pump with a hose, or an air compressor
- Stiff, flexible rubber sheet for a diaphragm. Many materials will work. I cut up a rubber 4" pipe cap.
- PVC pipe glue and cleaner
- Teflon tape for sealing threaded pipes
- PSI gauge which can do 0-100 PSI
- A drill, and a Tap and Die set would be helpful too
IMPORTANT: Make sure you have a lip inside the back of the 2" pipe or size adapter, because the diaphragm needs to rest against something! You'll probably want to get a screw-in size adapter so you can use it as the lip for the diaphragm.
Well... Just put everything together as shown in the pictures and diagrams. Don't glue on the size adapter for the back of the gun, because you'll need to open it occasionally to adjust or replace the diaphragm.
It may be worth noting that drilling and threading holes using the tap and die set can be difficult if you've never done it before. But you really do need to thread the holes, since the parts won't work otherwise.
(Better Instructions Soon?)
Experimental Test Results
|PSI||10 PSI||20 PSI||30 PSI||40 PSI||50 PSI||60 PSI|
Here are the results for the "vertical shot" test, using a tape bullet instead of a paintball. The estimated velocity from these measurements (based on simple Newtonion physics) are inaccurate by a factor of 4 or so, according to the paintball store's equipment.
|12 psi||3.69 s||54 feet up||59 feet/s|
The diaphragm I'm using is the second one I've tried. The first was made from a plastic coffee can lid with part of a rubber jar-opener attached. It worked great for pressures up to 40 PSI, but got dislodged at higher pressures. The new one seems to have no upper pressure limit so far.
My gun does something weird if I release the pressure slowly. If I hold the release valve barely open, the gun will make a long, loud resonant tone. It's neat. The first diaphragm didn't do this, but it did make a goose-honking sound. :)
My diaphragm is stiff enough that it holds about 6 PSI after shooting. This leaks out over a minute or two.
The diaphragm also seems unable to hold pressures of 6-10 PSI for very long. There doesn't seem to be enough pressure to keep it from leaking out. However, my old diaphragm held this just fine.