I used a "schrader to presta" adapter as the main body of the valve (gold part. it's real gold for real Xplosive results. true story)
the length of the aluminum tube (well, I took aluminium, I don't know why, it works with other.) is 132mm.
its exterior diameter is 4mm
tools needed :
a electric drill with wood (for the plastic) and metal drills
+tools from chluaid XRV tutorial
extra material :
universal flexible pump adapter from decathlon : http://www.decathlon.fr/raccord-flexible-universel-id_5553480.html
the red plastic adapter to inflate balloons (came from a pump)
+materials from chluaid XRV tutorial
Step 1: Overview
the red part is a inflating piece for balloons, I got it with the pump.
light blue part is the schrader end of the flexible I got with the flexible universal adapter.
black squares with small blue squares inside are auto-stop nuts. very handy! in chluaid tutorial he glued simple nuts, I found the auto stop ones in my drawer so everything can be de-assembled.
green part is the "schrader to presta" adapter, also from the pump.
black stuff is for screws and stuff.
# How it works
The drawing is made with the gun armed. when you pull the trigger, dark blue part goes forward (pushed by the original spring that I didn't remove). the purple part is glued to the dark blue one, so it pushes also the green one and the valve opens. the dark blue part moves only a few mm and is then blocked by the auto-stop nuts and the spring that cannot be compressed anymore.
I will make 1step for every part.
Step 2: Light Blue Part : Schrader End of Flexible
2. cut with the metal saw the small end of it (I had to hold it with my fingers I lack proper tools, so the sawing is quite horrible)
3. drill with 4mm metal tool a hole inside. watch out to not mess up the filet part.
Note : I made a few rounds will drilling to enlarge a little the hole, so that the center aluminium tube will go smoothly through it.
Step 3: Red Part : Pump to Balloon Adapter
I have removed the accessory hook on the side, made the cut smooth with a cutter
it's inner diameter is 4mm at the rear and smaller at the front. As our aluminum tube is 4mm, I've cut the small part that was going to reduce the flow of air. the foam dart will still have no problem to center in it.
Step 4: Orange Part : Front Canon
As the schrader adapter (light blue part) is larger, I made a hole of 10mm at the rear of the canon so we can pass it through.
at that time I didn't know that there was moving parts inside the Canon (plain orange-ish part) but it worked nonetheless. it ended with the "plain orange-ish part drilled instead of a theoretical wall I was thinking about
you can keep the spring inside if you did not mess it up. it won't be used anyway.
note : for the rear canon that I machined before this one, I used metal tools to drill and it messed it up, fortunately I had to make a larger hole so I could fix it with a WOOD tool that is much more suited for this ductile orange plastic. so yeah, use wood tools for drilling. please.
Then assemble with your little fingers the red part and the light blue part : put the red part inside the canon from the front, and the light blue from the back. screw them together as tight as you can (not easy to hold the red one without proper tools)
Step 5: Dark Blue Part : Rear Canon
pop the purple part out with a small screwdriver and keep it aside.
make a nice looking hole (not like mine on the picture, that was my first hole on this nerf and I used metal drills instead of wood) of 10mm through the inside wall. this part should look almost like a simple cylinder now.
Step 6: Purple Part : the End of the Canon
glue it to its original position on the dark blue part.
Step 7: Assembly
the nut on the left is used to fix in place the moving part of the front canon (orange part). I found that 83mm from the purple part is a good Distance. other distances are not that important (total length of tube, although I would not go under 120, compression of the spring etc. )o
I have put 2nuts to block the spring because the trigger mechanism will make the green part hit hard those nuts (ahem) and can make them move.
What I did after taking the pictures is to make a stack of auto-stop nuts from the ones on the right to the one on the left so everything is well fixed and cannot move. this is where the cylinder of the purple part that you cut in the previous step is useful, it can help stacking up nuts if you don't have enough (and no need to go higher than 6 auto-stop nuts, they are strong enough.)
Note : you can see I have cut the rear canon but that is from a previous trigger mechanism. like that you can see better.
1. take the dark blue part.
2. insert the valve + nuts (2nd picture) from the front of the canon.
3. insert the front canon with the red and light blue part already assembled.
The insertion inside the gun itself is really tricky : you have to put it in place while the outside spring is compressed. took me 1 hour.
Step 8: Conclusion
My main fears are that the airflow will be too small for the foam dart to pop out of the canon, and/or that the air leaks at the rear of the front canon will make everything useless. if I knew more about the moving part inside the Canon, I would have perhaps make things differently. after the drilling I could still make the mechanism but the permeability of the canon was compromised.
In a second part that remains to be done and written about, I will assemble a small airtank that on one end will attach to the rear of the Nerf, and on the other hand will have a real schrader valve.
Do not hesitate to comment, make suggestions or criticise my English!