Robot mounted air cannon

[math311]

Last year the seniors on the team built an air cannon, well sort of. They built the tanks, which are linked together with a splitter, and then attacked an electronic valve. Then they left for college. At the moment we have a 2 or 3 inch barrel, and that could work. problem is, we have nothing else for the cannon. We have last years bot to mount it, but it has no code for pneumatic s, and the only programmer on our team right now does not think they know how to make it work. Does anyone know what we need to do to make it robot controlled, so we can drive and shoot t-shirts?

[daniel_dsouza]

Hey cool!

Our team is debating whether to build one as well.

A simple robot mounted cannon: http://www.chiefdelphi.com/forums/sh...t-shirt+cannon

However you could also reach for the sky with a system like team 254's Shockwave robot. Lots of info here: http://team254.com/shockwave/

Thread discussing team 254's Shockwave robot: http://www.chiefdelphi.com/forums/sh...t-shirt+cannon

And your can always try searching CD for more threads, or searching the net for a (non-FIRST) example. However, remember that some examples aren't guaranteedto be safe. You would really want to carefully design any system that would be used for the general public.

Hope this helps,
Daniel D'Souza

[flameout]

I'll make the assumption that the valve wired up for the launcher can operate on 12 volts (we use sprinkler valves for our launcher -- they seem to work fine).

To set this up, you'll need to create a pneumatics system (you didn't mention any difficulty in mechanical, electronics, or pneumatics, so I'll assume you know what you're doing there), but instead of piping the output of the regulator to Festo solenoids, pipe it into the barrels. Then, attack an additional Spike relay to your bot, and wire the valve to that.

You didn't state what programming language you're using, so the specific implementation may differ, but in general, you'll have to do a few things for this system:
1) Create a Compressor object (obtain a reference if in LabVIEW)
2) Start the compressor (I'm not sure if this is necessary -- my guess is that it is).
3) Create a Relay object (obtain a reference if in LabVIEW)
4) Set the Relay to either output a Forward signal or an Off signal, based upon the state of a joystick button (this could be done with a joystick VI, ternary, and Relay VI in LabVIEW (I'm not sure what they're called exactly)).

Also, a note of warning: do not use PVC for the tanks. PVC is not designed to hold air, and can potentially explode with no warning. If the tanks are PVC, then please replace them with metal ones. You can find more by doing a search for PVC on ChiefDelphi.

I hope this helps.

[Fireball9199]

I could have sworn that one of those seniors was me.

[Phyrxes]

If your team is located at a school, please make sure the school district is okay with you constructing this. By many states definitions a pneumatic device is still classified as a "firearm" which may mean serious headaches with the district.

[math311]

Originally Posted by flameout

Also, a note of warning: do not use PVC for the tanks. PVC is not designed to hold air, and can potentially explode with no warning. If the tanks are PVC, then please replace them with metal ones. You can find more by doing a search for PVC on ChiefDelphi.

I hope this helps.

The seniors that built this used PVC pressure rated for 250 PSI, and we only plan on doing 125-150 PSI, so would that make PVC safe to use?

[flameout]

Originally Posted by math311

The seniors that built this used PVC pressure rated for 250 PSI, and we only plan on doing 125-150 PSI, so would that make PVC safe to use?

No -- PVC is rated for water, not air.

The (most important) difference is that, because water is practically incompressible, a small crack will turn into a leak. Air will cause the PVC to shatter entirely, creating a large pressure wave (permanent hearing loss) and large quantities of high-velocity shrapnel.

Also, I'm not sure if this is true or not, but I recall reading that the different type of loads experienced by storing air (particularly when all the air is released at once, as is done in a T-shirt launcher) can cause PVC to fail much more quickly (and randomly) as it does with water (even if you're only running at 10 PSI).

If you don't have metal tanks, they can be pretty expensive to buy new. We acquired our tanks from local medical-supply businesses. They may have tanks around that are too old to be useful or are being phased out -- since they operate them at 2000 PSI (this can vary -- I'm using the figures for Lincare), they have to be a lot more careful than us with regards to discontinuing use of old tanks. It can be hit-and-miss, though, because they'll occasionally have the tanks they've collected recycled.

Thanks for considering our safety concerns, and good luck constructing your launcher.

[IndySam]

Originally Posted by math311

The seniors that built this used PVC pressure rated for 250 PSI, and we only plan on doing 125-150 PSI, so would that make PVC safe to use?

I think the important point as sated before is that this rating is for water not air. These two things behave totally differently.

The odds are there will not be a failure or even if there is one it probably wouldn't be bad, but if there is a failure there is a chance that it could be catastrophic and very dangerous. This is simply not worth the risk.

You don't need to use expensive metal tanks. Black iron pipes in sufficient sizes are cheep and available at most of your big box hardware stores. There are also multiple fittings available to make the job even easier.

[math311]

Originally Posted by flameout

No -- PVC is rated for water, not air.

Well then i'm and idiot, but a lucky one, because that 200 PSI in one my friend built didn't kill me when he left the compressor on.

[EricH]

Originally Posted by math311

Well then i'm and idiot, but a lucky one, because that 200 PSI in one my friend built didn't kill me when he left the compressor on.

Yep...

One thing to remember: It might not fail on the first time or two. It might not fail on the tenth, twentieth, or thirtieth time. (Cyclic loading, fatigue, and a bunch of other stuff like that all play into when it fails--look in a machine design textbook for a better explanation.) But, you never know exactly when it will fail--it might fail the first time. And when it fails, you will know it failed, and hopefully you aren't within shrapnel range.