Can-Can-on by Schlauncha

Last crawled date: 3 years, 1 month ago

The .step and .iges files show all the plumbing fittings used, 10' long 3" diameter barrel surrounded by a 6" diameter pressure chamber 8' long, with a piston valve at the rear. 3D printed spacer keeps the 3" schedule 40 pvc barrel centered up in the 6" schedule 40 pvc pressure chamber. At the breech, a 1" pipe connects to a modified sprinkler valve, which dumps the air from behind the piston to suck it backward, allowing all air pressurized to 90psi in the chamber to now slam out through the barrel. A full pop can, placed in the sabot (printed with flexible TPU, like the valve) will be accelerated to roughly 500fps, with more muzzle energy than a 12ga shotgun. I am only posting this for information that is interesting, and I do not recommend anyone build this, because it will launch things farther than you can see, which could be dangerous if not used properly.
-- BUILD NOTES --
Fittings and materials needed:
All fittings should be Schedule 40 and/or list "PW", especially 6" fittings
10 feet of 3" schedule 40 pvc tube
10 feet of 6" schedule 40 pvc tube
Fittings in order of front to rear:
3" Tee (alter by adding hold through for muzzle brake, I used a lathe for this)
3" to 4" adapter bushing (alter by removing lip inside so 3" pipe slides through)
4" to 6" adapter bushing
6" pipe to 6" male thread adapter
6" female thread to 6" pipe adapter
8 feet cut from the 6" tube listed above for pressure chamber
6" schedule 40 pipe-to-pipe connector
6" to 4" bushing (alter to remove lip inside so 4" pipe slides through)
4" schedule 40 pipe-to-pipe connector
4" to (smaller) bushing
(smaller) to 1" NPT female thread bushing
1" NPT pipe 9" long extending to the rear from the last bushing
Going back to where we had 4" pipe now,
4" to 6" bushing (only glue to 4" pipe, and perhaps sand down outside slightly)
6" schedule 40 pipe-to-pipe connector (do not glue to bushing)
6" schedule 40 pipe approximately 6-8" long, so next fitting fits up flush as shown
6" pipe to 6" NPT female thread adapter
6" NPT threaded screw-in cap (alter with 1" clearance hole in center, add fittings for fill & trigger)
1" NPT threaded reducer tee (this goes onto the 1" pipe coming from the breech)
Reducer bushing going in reducer tee to get it down to 1/8 NPT female
1/8 NPT male 90 degree 1/4" air tube connection
The following gets mounted in the rear screw-in cap, using it as a solid wall and providing the air hose connection on the rear for filling:
1/4" air tube connection to 1/4 NPT female (may need a few pieces to adapt this)
1/4 NPT male air hose coupler fitting
Back to the tee, coming straight back in-line with the centerline:
1" NPT sprinkler valve, modified to remove solenoid for faster direct triggering
1/8" NPT male 90 degree 1/4 air tube connection (threaded in where solenoid was)
Several feet of 1/4" air tube coming from the sprinkler valve's trigger back through cap
1/4" air tube to 1/4 NPT fitting
1/4 NPT tee
Pressure gauge off the side of the tee
1/4 NPT male-male short adapter
air blaster screwed on as the final piece, the trigger
Prime and glue everything (except the threaded joints, and where the rear "can" slips over the sprinkler valve area) and make sure to use thread sealing tape on all threaded connections. The piston could be 3D printed as shown above, although currently I am just using a rubber cap for 4" tube glued over a 4" cap glued to a short piece of 4" tube, and then a 4" to 5" clay pipe rubber adapter that is flipped backwards so its larger diameter end (roughly 6" diameter outside - fitting the pressure chamber) is right around where the 4" tube cap is. The flat face of the 4" rubber cap is what seals against the end of the 3" barrel - I set the gap by putting a roll of duct tape in the breech, along with the piston, screwing the glued bushings into the front of the pressure chamber, and then taking the not-yet-glued 3" barrel and sliding it in until it hit, and gluing it there. After it cured, I unscrewed the barrel with its front bushings at the front 6" thread (the muzzle brake allows a smaller tube to pass through for leverage for unscrewing), and removed the roll of duct tape, leaving the piston with a few inches clearance to travel forward/backward between the breech and barrel. The inner end of the 3" barrel was carefully sanded very flat and perpendicular to the barrel's axis, so the valve would seal against it well. Procedure is to connect the air hose and allow it to pressurize to at least 20PSI (perhaps use a ball valve to control filling) so the piston seats to the barrel, and then load your projectile. If you load a projectile with zero pressure, the piston won't be up against the end of the barrel, and any wadding you have behind the projectile (I like using blocks of pillow foam) will expand out the back of the 3" barrel, preventing the piston from sealing against it. If the piston starts slightly pressurized so it's already sealed, then this isn't an issue. Once loaded and fully pressurized (I run 90PSI based on my air compressor's limitations) then when the air blaster is squeezed, the sprinkler valve's diaphragm now has low pressure behind it that you just vented, so the high pressure from inside can pop it open and flow out fast. This means that inside the breech, the pressure is holding the piston over the 3" barrel for starters, with 90PSI both ahead and behind the piston since it isn't a perfect seal, so it wants to stay forward as a cork in the only hole it sees low pressure, the 3" barrel. But when the sprinkler valve dumps out the air from behind the piston, now the piston has 6" diameter of low pressure behind it, 3" of low pressure ahead in the barrel, but the rest of the storage chamber is still pressurized to push back on the front of it, so it incredibly quickly will move to the rear, opening wide for all the chamber pressure to flow out the front.
Sorry for the rushed write-up, I just wanted to get a bunch of this info added to start with so it's at least listed.
Video of test firing (sorry for vertical video - I wasn't the one filming)https://youtu.be/_vxRjVACCRQ
Update 18MAY2017: added "rifler print" .stl files for tool that holds 6 pipe cutter replacement wheels (Plumb Works #694-3873) to pull through 3" schedule 40 PVC and cut rifling. Added "valve metric.stl" which is printed in flexible TPU and has tested successfully so far.
Update 30MAY2018: added parts for 4" barrel usage, such as concentrificator ring and sabots for baseballs and soda cans. Also added "Soda dart" which is a fin-stabilized projectile for holding a can of soda, where the fins spring inward as it is loaded into the 3" barrel, and they deploy by spring-action of the TPU material as it leaves the barrel. This is all a work in progress still, it seems we have problems with valve function now that we went to 4" barrel, but at least the 3" worked well. Another video if it wasn't already posted: https://youtu.be/-Bn7iZ-3Owk