Barrel uses an interrupted screw breach to connect to the valve. It only requires a 1/8 turn to lock into place.
Cannon with old PVC barrel adapter
https://youtube.com/shorts/2kzszOEqZ1g
I made the air tank first. It uses an off the shelf 2” PVC threaded pipe to connect to the valve. The carbon fiber was applied via a wet layup and then coated in a tinted epoxy gel coat.
The barrel was made by a new DIY pre-preg process I’m still workshopping. Real pre-prep is fairly expensive. This DIY process aims to replicate most of the storage and application benefits at a fraction of the cost.
The DIY pre-preg is made by sandwiching dry carbon in between two layers of painters drop cloth (4 mm PET film). Epoxy is then poured over the carbon followed by spreading the epoxy by squeegeeing it through the PET film to keep everything clean.
I let the wetted out carbon-PET sandwich sit in a cooler for 24 hours. The epoxy eventually cures and cools to the point where it functionally acts as real pre-preg. I can cut it into shape without getting scissors overly stick, I can easily remove the PET backing, and it’s just sticky enough to stick onto the PETG parts and itself without being too sticky to actually to work with.
Once all the carbon’s been applied to the parts, I wrap it in more PET film, throw it in a vacuum storage bag, and compress it for three hours until it’s no longer sticky to the touch. I then cure it in electric smoker set to 100 F for 8 hours.
Total air tank volume is 6 L. I hydrotested it up to 100 PSI without issue. Normal operating pressure is between 15-40 PSI.
With the 36” carbon fiber barrel and the tank pressurized to 40 PSI, I fired two chuck it ultra balls at the same time 158 yards with an estimated muzzle velocity of 151 mph. I’ll have to do more testing with a single ball and actually measure the velocity, but I’ve gotten around 250 mph at 60 PSI with an 18” PVC barrel before.
I use Total Boat High Performance slow cure epoxy and Elegoo Rapid PETG. I use PETG over PLA so it can better handle the higher oven cure temps without deformation. ABS would be even better since it bonds better to epoxy, but I don’t want to deal with the toxic fumes.
I still need to workshop the DIY pre-preg process. I’m trying to figure out how to get a nicer finish on the surface. I’m going to try doing another gel coat after the initial carbon application and using a 1 mm thick PET film to hold it in place and keep it from dripping. If all else fails, I’ll just have to do thicker coats and sand it a bunch.