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Originally Posted by KohKohPuffs
The valve I'm using for my t-shirt cannon was this:
http://www.ascovalve.com/Application...IsTran sSSL=Y
Uh... that's a really long link, but it should direct you to something I found while browsing CD for info on t-shirt cannons.
Now what kind of air tanks are those? I'm having some issues finding the right one, and those look really great for my design  |
Honestly, I just sort of created that model based on my ideal dimensions of a 1 gallon tank. The interior volume is 1 gallon, but everything else is guess work.
That said, the tanks that otherguy posted are only 1in longer and a bit smaller diameter, if this is to be built, something like that would probably be used instead.
Quote:
Originally Posted by otherguy
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Thanks, this seems to be a better fit than anything else I've found for this design. Would you be able to post the dimensions of your tank by chance? The site shows 4” x 15.5” but I'm not sure if that includes the mounting brackets, or if it refers to the tank diameter.
Quote:
Originally Posted by GeeTwo
We brought our rebuilt air cannon to Homecoming last night, so I have a few comments, some positive, some questioning:
6 pneumatic wheels: We are using AM pneumatic wheels with the long (31") nanotube gearbox. It does not turn very well as far as small radius is concerned. We were able to make a sharp turn, on the boardwalk to get into the shed, but it required about a nine-point turn. For sweeping curves, it drives fine! If you want a highly maneuverable robot with pneumatic wheels, I recommend significantly more than a 1/8" center drop.
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Currently the drive is designed for a 1/4" drop center. I picked 1/4" figuring that the standard 1/8" would be inadequate for the squishiness of the wheels, but it was still basically a guess. Should I have a bigger drop then 1/4"? 3/8" perhaps? 1/2"?
Quote:
Originally Posted by GeeTwo
Magazine: we've skipped this level of complexity; we have two muzzle-loaded barrels. Consider whether you're really up to it!
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There would definitely need to be prototyping done first to prove the concept, but based on what I've seen from mechanisms other cannons have used, it seems plausible. The mechanism that seals the shell to the barrel is actually based off of
this design posted a few years back. The rotary loader is by far the most complicated part to make but not impossible.
Quote:
Originally Posted by GeeTwo
T-shirt shells: we've developed a method to roll t-shirts which is very similar to rolling socks, and ends up flipping a sleeve around the bundle. It works well for us, but we do still load down the muzzle.
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I saw that method you posted on one of the other T-Shirt Cannon threads recently. It's definitely something we'll look into. We had pretty good luck using rubber bands in our tests with an air cannon a mentor brought in, but not having to bind the shirts at all would be ideal.
Quote:
Originally Posted by GeeTwo
Variable Angle: we started to design for this, and found it to be of limited utility when we did the math, especially when we decided that we never wanted to throw a t-shirt or football directly at anyone, Sandy Koufax style, but would rather do it mortar-style to reduce the likelihood of bruised faces.
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In most cases, the lower angles would not be used for firing the cannon (and in fact, we've discussed disabling the firing mechanism at low angles for safety), but instead for transporting the system. In most situations the cannon would fire mortar-style. The variable angle system itself is not very complex to make either (gas spring + winch) so it wouldn't be a huge loss of time to add it.
Quote:
Originally Posted by GeeTwo
Air system: 2 gallons is probably sufficient (ours is around 4, but we got the tank surplus). The most important features are the size of the pipe leading out from the accumulator to the valve, and the size of the valve. I recommend a minimum of 3/4", and a preference of 5/4" or larger. We currently have a pipe from the accumulator to the solenoid valve of 1"+, a 3/4" valve, and 3/4" rubber tubing to the barrel, which works great with 50-60 psi and about a 50ms valve-open time.
Bore size: the smallest point on our current air cannon is 3/4". It's been adequate, but if we were buying today, we'd go for 1" or larger all the way from the accumulator tank to the barrel inputs. Added: For the barrel, we're using a 3" bore. We had 2-1/2" previously, and it worked well for shirts, but the foam footballs got stuck. We went to 3" and roll the shirts thicker and shorter.
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My target output valve size was about 1" since that seemed to be the easiest to find. I am curious though, what are your thoughts on using multiple smaller valve tanks and combining them using larger size Tee connectors and bushing adapters? Could you, for instance, combine 4 1/4" feeds and get the equivalent to a single 1" feed? I ask because I'm finding it difficult to locate small tanks (<= 0.5 Gallon) to use for an accumulator that also have large output ports (~1").
Also, do you have any suggestions for large (~1") ID pneumatic hose? I'm not sure what type to look for or where to look (the only pneumatics I've ever dealt with have come in the FRC kit of parts).
Quote:
Originally Posted by GeeTwo
Air compressors: we're using a scuba tank. When we considered not doing scuba as a supply, the best solution seemed to be to have a 110V compressor under the stands where we would go back to recharge every 10 or 20 shots, rather than trying to compress air from a 12V FRC battery. With a larger marine battery, perhaps you could make battery-powered recharging of the accumulator feasible. Last night, we used a single battery to drive and activate solenoids; we did not use either of our two spares. Had we been dependent on FRC-legal batteries for air pressure, I suspect we would have had to replace those 3 batteries at halftime.
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I considered Scuba tanks and even Co2, my concern was the repeat cost of use for these (as Scuba tanks have to be refilled and Co2 cartridges replaced). My hope is that by using a separate battery for the air compressors, the battery can be swapped without having to reset the robot itself, allowing for faster change out times. The compressors are also rated for continuous duty, unlike the standard FRC compressors, which I would think make them more efficient. Plus, by using rechargeable batteries, the cost to use is essentially zero (aside from the cost of the items you're shooting of course).
Quote:
Originally Posted by GeeTwo
Release valve: whatever you use, be sure it is rated for air, not just water!.
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I've seen enough threads on this topic on CD to know to avoid non air-rated valves.
That said, I'm curious what people think about using PVC for the barrel. It seems to be quite common, and I would think since the barrel isn't really storing air pressure it wouldn't be a problem. People I've proposed this idea to have mixed feelings about PVC despite it being used in literally every example cannon they've showed me.
Quote:
Originally Posted by GeeTwo
We're also using a 3" id barrel. I haven't figured the volume, but we're using a 3/4" nominal diameter solenoid valve, and opening it for about 50 ms, utilizing 30-70psi (most commonly 50 psi). With 40-60 PSI in the system, it puts shirts anywhere in the stands we want to. With 70+ psi, we can toss a t-shirt over the top of our home-side stand and onto ninth street if we fire directly perpendicular to the stands. Foam rubber footballs don't take quite as much pressure x time to get to a given location as do t-shirts.
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In tests we did with a handheld air cannon, it took about 90psi to get the sort of range performance we were looking for when shooting shirts, but that said, the cannon used a manual lever valve and may have had an inadequate accumulator tank. My intention is to find an electronic pressure regulator so the working pressure of the system can be changed on the fly, allowing for a variety of shots.
Does your cannon (or anyone else reading this) use a 2-stage air system (storage->accumulator), and if so, what is the volume of the accumulator?