We Need A Bigger Cannon... and a VersaLaser!
300 yard tennis ball hucks? No problem. Your questions about calculating barrel to air chamber ratios, finding fittings and what exactly Schedule 40 is? No problem. David's new Versalaser? Problem: he's out sick!
We had a some questions in email and on the boards about the cannon, and we wanted to show you our bigger air cannon in action... plus we tease Ranolph's new toy: a VersaLaser.
Ranolph's already etched multiple notebooks, wood, aluminum and, we think, some titanium! (If not, Patrick wants his Ti spork etched!)
Randolph's out sick as a dog, so do us a favor and send him some healthy vibes, so he can get back to work with us on custom iPod cables for Mike and Jeff, did you say ... a coil gun? (Jeff, I'm gonna leave that one up to Dave!)
Turbocharging Your Sprinkler Valve:
On our big cannon, we went with an air triggered 'turbo charged' sprinkler valve. We also went with RainBird sprinkler valves, which seem to moan a lot less than the Orbit valves we used for the smaller cannon. Doomlabs Turbocharging Sprinkler Valves was invaluable for sorting out how to tweak the valves for more oomph.
The downside is that this makes it super easy to accidentally release your tennis ball. Always point it down range. The dual electrical switches in the smaller cannon are definitely more safety conscious.
Now... about those pneumatic cannon questions:
Q) How do I choose the right parts?
A) Think Legos: you're gonna mix and match based on what's available at the local hardware store, or what you can order online. Hint: fewer parts and fewer joints is better! Want some ideas on the kind of fittings that are out there (from caps and couplings to reducers and wyes?) Check Harvel's PVC component pix, PlumbingProducts.com, PVCFittings.com and Lasco.
Q) What's all this schedule stuff?
A) Schedule = the thickness of pipe wall, in "Nominal Pipe Size (NPS) a set of standard pipe sizes used for pressure piping in North America."
The outside diameter is stays the same, but the inside wall thickness increases with the schedule as you move from Schedule 40 to Schedule 80. (And, we assume, to Schedule 120, etc.)
We've been using Schedule 40 PVC with a few Schedule 80 fittings (Those are the grey ones) which is more than strong enough for the 115 PSI we're gated to with our safety valve.
Q) How do you get the measurements for the barrel and air/combustion chamber?
A) Part 1: Volume = Pi x radius sq. x length--(in inches)
And he broke the sound barrier with this cannon, which had a 1.6 to 1 ratio.
We're experimenting with more volumes and longer barrels!
BTW, Spudtech is for sale... buy it so we can get some rifled barrels to play with!
Q) Why did you do a U-shape design? Wouldn't putting the chamber and barrel in a straight line be sturdier?
A) I chose being able to fit it in my car with out leaving a window rolled down over the potential performance boost of not routing the air 'round a 180 degree turn... plus, doubled up, it's got the whole BFG9000 feel to it. Don't mention that to the Homeland Security police that roam around San Francisco. (Did I mention making sure it wouldn't hang out a car window???)