Butt loading 63mm air cannon.
Posted: Mon Mar 20, 2006 2:58 pm
I've made this cannon out of 63mm (2.25") 150psi PVC tubes. It fits a Nerf perfectly and I truely believe that is way overdimensioned. It's about 125cm (50") long and it's of a blowforward design. It's a stacked tube design 
. The lower tube consists of the main air chamber (the long part), he bolt part (the T), the spool chamber (the short part) and the spherical 3-way (not shown). The top tube is the breech and barrel.
Here's the bolt. It's made out of PVC and it's hollow in the center with a one way valve. The smaller face seals the main air chamber while the big back seals the spool chamber. To load the air you simply connect the air through the 3way. That fills the spool chamber. This pushes the bolt forward sealing the main air chamber. The air flows through the bolt to the main chamber filling it. To shoot you just switch the 3way (manually) so you dump the spool. The maing air chamber pushes the bolt backwards liberating the air. It flows through the T to the breach which was sealled from behind with a drumstick.
This is a quick CAD I made. The Back o-rings are missing but you can see the grooves. And it lacks any sort of air color.
This is in the charged position. The black part is a rubber seal. The air in the T connector is at atmospheric pressure. On the right and left of the bolt is at 120psi. The air on the right has more area than the air on the left.
This is the open position. You simply dump the air on the right and the pressure on the left will push the bolt back, liberating the air through the T connector. I'm missing a little plate a put on the left (tip) of the bolt in such a way that when there's pressure from the right, it will move and allow the air to pass freely. But when you depressurize the right side, it will get pushed against the front and seal enough to let the air push the bolt.
We shoot this home made sabots. I don't know how do you call those foamy thingies. But are used by kids in swimming pools. When lathed to size they make excellent selas for the sabots. This sabot used a cut down cupboard. But later version only use cardboard.
Since the bolt might stick, I've made the two tubes separated. The passage is sealed with an o-ring and both parts are joined with a tow line. Some experiments broke some 120lb plastic seal (somebody knows the translation for Spanish "precintos"?).
The cannon is filled with a tire valve to 7bar (100psi).
Then the sabot or nerf (we don't have them here) is introduced.
The drumstick use is twofolt. First is used as a rod to push the sabot beyond the air connection (the T). Then is recessed to seal the back. In the picture the o-rings are placed in the wrong side. Sorry for that.
At las a simple SS pin holds the drumstick in place.
I've shot a 30 rounds sabot to 80m (~87yd). Beyond that, the spread is too much and the drum usually acts as an air brake at first. With 8.5 bars (125psi) I've chronoed it to 360fps.
Due its raw power it's used only for indirect fire. But I was wondering what you think about it and if it would make a good main cannon.
I'm adding a link to google videos I made as soon as those get verified.
. The lower tube consists of the main air chamber (the long part), he bolt part (the T), the spool chamber (the short part) and the spherical 3-way (not shown). The top tube is the breech and barrel.Here's the bolt. It's made out of PVC and it's hollow in the center with a one way valve. The smaller face seals the main air chamber while the big back seals the spool chamber. To load the air you simply connect the air through the 3way. That fills the spool chamber. This pushes the bolt forward sealing the main air chamber. The air flows through the bolt to the main chamber filling it. To shoot you just switch the 3way (manually) so you dump the spool. The maing air chamber pushes the bolt backwards liberating the air. It flows through the T to the breach which was sealled from behind with a drumstick.
This is a quick CAD I made. The Back o-rings are missing but you can see the grooves. And it lacks any sort of air color.
This is in the charged position. The black part is a rubber seal. The air in the T connector is at atmospheric pressure. On the right and left of the bolt is at 120psi. The air on the right has more area than the air on the left.
This is the open position. You simply dump the air on the right and the pressure on the left will push the bolt back, liberating the air through the T connector. I'm missing a little plate a put on the left (tip) of the bolt in such a way that when there's pressure from the right, it will move and allow the air to pass freely. But when you depressurize the right side, it will get pushed against the front and seal enough to let the air push the bolt.
We shoot this home made sabots. I don't know how do you call those foamy thingies. But are used by kids in swimming pools. When lathed to size they make excellent selas for the sabots. This sabot used a cut down cupboard. But later version only use cardboard.
Since the bolt might stick, I've made the two tubes separated. The passage is sealed with an o-ring and both parts are joined with a tow line. Some experiments broke some 120lb plastic seal (somebody knows the translation for Spanish "precintos"?).
The cannon is filled with a tire valve to 7bar (100psi).
Then the sabot or nerf (we don't have them here) is introduced.
The drumstick use is twofolt. First is used as a rod to push the sabot beyond the air connection (the T). Then is recessed to seal the back. In the picture the o-rings are placed in the wrong side. Sorry for that.
At las a simple SS pin holds the drumstick in place.
I've shot a 30 rounds sabot to 80m (~87yd). Beyond that, the spread is too much and the drum usually acts as an air brake at first. With 8.5 bars (125psi) I've chronoed it to 360fps.
Due its raw power it's used only for indirect fire. But I was wondering what you think about it and if it would make a good main cannon.
I'm adding a link to google videos I made as soon as those get verified.
