This is a work in progress concept of a T-Shirt Cannon robot I’ve been working on for the past few weeks. There’s still a lot of details to add but I thought I would post what I had on CD to see what people thought of it.
Runs on 2 FRC batteries (not sure yet if it would run off of both in parallel or if one would power the robot and the other would power the compressors)
Currently weighs about 100lbs
Small enough to fit in the back of a typical minivan
Possible Future Additions:
Sonar or LIDAR rangefinding to prevent accidental firing at low angles if someone walks in front of the cannon
Electronically controlled pressure regulator
Camera tracking for targeting (angle, range, etc.)
Other types of (“safe”) projectiles fired using foam sabots (various soft giveaway trinkets, candy, etc.)
For any of you who have worked on T-Shirt Cannons before, a few questions:
What type of release valve did you use (links would be great)?
How does the output bore size of the hose/connection going into the cannon affect the distance and efficiency (amount of air used per shot) of the cannon?
For a 3in ID barrel, what volume of air is required to fire effectively and at what pressure (I’m trying to find suitable storage tanks for the 2nd stage of the air system which is intended to be dumped completely for each shot, and then refilled by the primary storage tanks)?
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.
Magazine: we’ve skipped this level of complexity; we have two muzzle-loaded barrels. Consider whether you’re really up to it!
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.
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. - 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.
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.
100#, back of a minivan: ours is a bit heavier (130-150#), but it will fit in a minivan or even a small SUV or station wagon once the barrels are removed from the chassis (single 1/4" thumb screw). Our biggest “fitting” problem with our air cannon was fitting it through the doors in the classroom before a rebuild about 1 year ago.
Feature Additions: no comment, as no experience.
Release valve: whatever you use, be sure it is rated for air, not just water!
Compressed air has several orders of magnitude more energy than the same volume of water at the same pressure, so failures of air systems are much more destructive than water. Air-rated systems are almost always metallic, not plastic. This is because metal “tears” and plastic “shatters”. If you don’t want to put shrapnel in the operators or bystanders, use only air-rated pipes and valves. - 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.
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.
We built one similar a few years back and having shells preloaded is great for speed or for targeting sponsors (if we see on in the crowd at a football game we can load three in a row that contain their shirts).
We run ours off of CO2, and only at 12 psi for normal operation. We use one $14 tank for around 70-80 shirts.
I’ll put up a picture soon, the only part we haven’t figured out yet is the magazine. I like your solutionwith the rotart loading. We simplified a bit and used a pneumatic ejector and plan to spring load shells so they autoload when the spent shell is ejected.
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. :rolleyes:
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.
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.
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"?
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.
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.
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.
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).
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).
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.
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?
Could you, for instance, combine 4 1/4" feeds and get the equivalent to a single 1" feed?
Flow rate is proportional to the area, not diameter. Also, tubing is generally specified via the OD not the ID, so a 1/4" tubing might be closer to ~1/8" ID depending on the wall thickness you have.
Finally, tee fittings have a pretty significant pressure drop (relatively speaking). When you are discharging air in a cannon, your air flow speed is likely going to be quite high, so having a significant number of tees might be an issue. If they were between your high pressure tank and your accumulator, it wouldn’t be an issue, but everything that is “firing” when that valve opens needs to be relatively large with minimal pressure drop.
It’s going to depend on the length, weight, and tire pressure/size. If you can manage a design where the drop can be adjusted, at least for the prototype, that would be best. You want the drop to be as little as gives you the maneuverability, because a larger drop means less stability in remaining level. You can partially offset this by putting your CoM clearly ahead or behind the middle axle, so that the robot settles the same way each time you stop.
This is from a bit of thought, not experience: Fill a tire with air and put a quarter of the robot’s weight on it, and see how much the axle drops. I would use at least that much center drop, probably a bit more.
Our barrel is hinged at the lower end, but we keep it in place with a length of rod. We can pull a pin and drop the barrel to a level orientation for shipping.
It would be less expensive and easier to trouble-shoot to use a single valve per shot. 1" should be adequate; we’re getting by with 3/4" at 50-60psi. As Steven noted above, you’d need 16 1/4" i.d. inputs to equal one 1" i.d. input (actually, more than that, as turbulent losses in a small hose are greater than a large one).
Google is your friend here. You can probably find a local company that deals in these items as well.
We got our scuba tank inspected and charged at a dive shop this week; I believe it cost $8.50. We get several hundred shots from a tank. When we don’t need inspection, we can sometimes get the local fire house to charge it for free, as we’re using it for educational purposes.
We’re using PVC for the final barrel right now, but plan to go to a metal tubing next year.
We have been able to toss shirts over our home stands with 60 psi, and over the press box with 70psi. This is using a 3" barrel and 3/4" valve, and 50ms of valve open time. Each of these numbers will affect how far you can throw an item of a given weight. Having a proper (snug, not tight) fit in the barrel is essential for maximum range as well.
Rather than change the angle, we are planning to adjust range by changing the duration that we keep the valve open. I believe we’re currently hard coded at 50ms, but we now have a more capable controller and will be adding variable timing.
You can find a picture of our semi-semi auto t-shirt cannon here. Apparently when you upload from an Android phone the thumbnail is upside down, but full size is right.
We have since ditched the FRC control system in favor of the Cheap and Dirty control system from Andymark. The FRC system was super unreliable and this one works up to about 350 feet away. For those shopping for a RC system you can find the same thing as AndyMarks without their stickers for less than half the price here.
We are a fairly average team looking for advice on a T-Shirt Robot. The idea is to train our team (Which doubled in size last week to over 25 members) by constructing this robot.
So I ask my questions,
Are there valves that will release the stored air we need to propel the shirt through a 4" barrel without modification? If so, what can you suggest?
Should we go with the air storage I have in the model, or something else? Should we charge it up with a ViAir? or a better Compressor?
Are there any good ideas to lift the barrel? We are wanting to use the Lead Screw method that our 2013 team went to St. Louis, but we are open to new ideas.
A bigger barrel means more air faster to propel a projectile. We use a 2.5" barrel and have been happy with that, a 3" would be nice for XL and XXL t-shirts though. There are valves that are capable and a few have been tossed around forever on CD, look to fast acting 3/4"-1" solenoids for this. We used a really cool hose from Parker Hannifin that requires no fittings and is available in those sizes with fittings being the biggest cost.
After running the FRC compressor to charge our cannon the first year of it’s existence, I will never do it again. We have times at pep assemblies where we have five shirts to shoot in ten seconds, and the little viair just isn’t up to the task. We use a 5# CO2 cylinder because it’s cheap, we have a discount to make it cheaper, and it is a lower amount of stored energy than a SCUBA tank. The only issues we see from this is that with liquid CO2, you can freeze your system forcing you to wait a minute if you fire rapidly.
Your storage looks to be PVC, but I can’t tell from the drawing exactly. Be ready to be attacked for that, and with good reason. Go find the videos of plastic tanks exploding for why. There are tons of safe high volume tanks available with large ports, you’ll just have to look outside of normal FRC vendors to find them. We got ours from Home Depot with a 1" port.
For lifting the barrel, go with what you like. We change ours by hand because we have only changed it a handful of times since we built it. Ours uses a CNC Plasma cut angle gauge and wingnuts to lock it in place. We had designed a motorized version, but the only time we lower it is when it’s in the trailer or if we are test firing and don’t want the height.
Everyone will go over a lot of details on high pressure systems and safety and a lot more. Design safe and stay safe. We use no more than 30 PSI and typically run at 12-15 PSI for shots from our track to the top of the bleachers at our football stadium, it’s around 200 feet or so. Ask yourself if you need to shoot further, then ask yourself why…
Look on Google. We use one similar to this. If you can find one that’s a bit larger (1" or 1-1/4"), even better. The most important thing is that the valve (and plumbing and tank and fittings and so forth) is rated for air, at a higher pressure than you’re using. A large valve (3/4 NPT or greater) is essential to get enough air out fast enough to throw a t-shirt very far without using pressures higher than we’re used to in FRC.
I don’t know what takk you have in the model, and we don’t move our barrel vertically, but control range using the time the valve is open, so I’ll pass on the other two questions.
We had decided on 4’ because the ease of loading the way we learned to fold shirts, but 3’ to me sounds more feasible, if we can load it properly. I would love a link to that hose, ABS wont cut it, too much conversion.
After running the FRC compressor to charge our cannon the first year of it’s existence, I will never do it again. We have times at pep assemblies where we have five shirts to shoot in ten seconds, and the little viair just isn’t up to the task. We use a 5# CO2 cylinder because it’s cheap, we have a discount to make it cheaper, and it is a lower amount of stored energy than a SCUBA tank. The only issues we see from this is that with liquid CO2, you can freeze your system forcing you to wait a minute if you fire rapidly.
We could look into CO2, but the shop teacher lost a chunk of flesh on his chin to CO2 Canisters due to a careless woodshop kid, so he may not take kindly. It is a great idea and im curious to see how id work.
We work with a lot of Home Depot parts, (being near our school) so ill check that tank out, a link would be awesome. We are very careful with our tanks, we work behind protection and we dont take unneeded risks. Trying to get the new guys to do this will be an adventure, im trying to expose to everything you can use on a bot for 2016. Finally, like I said, poor school means no CNC Plasma 3D Printer though!
Look on Google. We use one similar to this. If you can find one that’s a bit larger (1" or 1-1/4"), even better. The most important thing is that the valve (and plumbing and tank and fittings and so forth) is rated for air, at a higher pressure than you’re using. A large valve (3/4 NPT or greater) is essential to get enough air out fast enough to throw a t-shirt very far without using pressures higher than we’re used to in FRC.
Like I said, we will use a 1" Valve on our bot, thanks for suggesting this valve, its a great price (which we are worried about). We need to REALLY reduce the pressures we use, being that they are many times higher than cannons ive seen (though we are using a sprinkler valve). I think our lead screw lifting idea will work, but we are considering a mortar style instead.
The valve we run is a check valve run in reverse. We move the whole valve and engage it into the shell to release the valve. Clear as mud? I can try to get some pictures that will be rightside up this time to help out if not.
We had to do a little machining (i.e. sanding and filing) to make a threaded end that would fit inside our valve.
We actually run a plastic valve that has a burst rating of 200 psi and is rated for gas to 100 psi. I don’t remember where we got it from though.
Our tank is a hot water expansion tank likethis. Yes it is for water and not for gas, but we are running at less than 20% of the rated pressure and it is a steel tank that has a safety vent built in.
We have had no issues and pressure tested one to 130 lbs prior to using it by filling it and draining, repeating then using some force to deform and filling and draining again. No leaks, no failures, and no worries with 10-30 psi being contained.
The benefit of how we built ours is that we use a cylinder to push the actuator to release gas. If we pressurize over 30 psi the regulator on the cylinder won’t allow the cannon to fire or engage. It just hisses a little and reminds you that you are trying to do more than was designed for.
706 uses a pony scuba tank
Last about 30-40 shots.
The tank cost us something like $120 but with that we get free refills. We had to get a supplier to build a custom valve to handle the 1/8 hose. That feeds into a storage tank that holds
60psi. We usually shoot at something between 20 to 40 psi.
With this set up and how fast the scuba tank recharges the storage tank we can shoot all 10 of our stored t-shirts in something like 15-20 seconds.
Look on ebay for some 12volt air solenoid valves, I found ours rated at 215 psi and 3/4 npt threads. Fast open and close and no leaking. Cost was about $30 each.
Magical stuff, just be sure it is the length you want before you install. Look up local industrial suppliers or use the where to buy link on Parkers site. I used to work at the Brass Products Division in Otsego, MI. They are very friendly to FIRST teams and we get donations from time to time. Might be worth a kindly written email or a phone call to the proper division.
HOSE PRODUCTS DIV
30240 LAKELAND BLVD
WICKLIFFE
OH
UNITED STATES
44092
A 3/4 is good but our team really wanted a one inch. The school district is not allowing us to use CO2 Canisters of any type, they are already edgy on us making a tshirt cannon robot. I’ve having a lot of trouble finding a high pressure solenoid, so should we settle with a 3/4"?
Once again, thanks everyone for the feedback, but i need to identify a list of objects (Tank,Hose,Solenoid,Barrel) which could be all be strung together and put on a robot. we have 20 new members waiting on the design group to finish the model for this bot.
3D Printer though! 