FIRST air cannon robots PVC??

[FourPenguins]

Don't use PVC unless you absolutely have to.
If you do use PVC, wrap it in duct tape so that if it ruptures, the fragments won't kill you. One member of our team had a near miss when a PVC tank blew up. He made it out with a nasty scar on his forehead, but he could have been much less fortunate.

[Donut]

Originally Posted by Andrew Schuetze

This was indeed prototype 0.1. I used 8 KOP tanks in four parrallel circuits. I.e. two tanks in series feeding into a manifold with four inlets. The manifold was all 0.5" black pipe tees. I then used couplings to enlarge the opening to the 1.0" diameter for the sprinkler value. Not nearly enough air flow was generated to launch the tee shirt out of the 3.0" diameter barrel.

I'm looking at an alternative now, if that method didn't work for you I really can't see it working any differently for us especially with the same barrel.

[KenWittlief]

Originally Posted by Billfred

I get the basic concept, but what would work for the pin? It'd have to be something strong enough to handle the force of the cylinder, yet also be able to be yanked out of place (or so I think).

it could be something you pull like a trigger on a gun. It doent have to be pulled out of the way quickly, because the cylinder is already pressurized behind the stop.

Also, I think the largest cylinders you can get from the supply list has a 2 foot piston. That should be big enough to shoot just about anything!

[Gdeaver]

A Sabot casing for the tee shirts would cut down on the volume of air and flow rate needs. Properly designed the sabot casing would only go a couple feet. Sabots need a very smooth bore. Seam to remember a few casing designs for water balloons online. Starching and a tight roll will keep the shirt in a good projectile form.

[Matt H.]

Our team is working on a similar project. We considered the use of PVC, but decided to use a tank instead. Our local Walmart sells a 7 gal 120 psi tank for 20 dollars; the decision to use the air tank is about as expensive as PVC tanks would be for a similar volume and has left everyone on the team feeling safer. If you do use PVC consider netting around the PVC similar to that used around pressurized laboratory glassware.

[amos229]

not that i support nor encourage the use of pvc for pressure tanks i have heard however of wrapping the pvc tanks in many layers of duct tape incase of a blowout it prevents shard from injuring someone. just a thought.

[KenWittlief]

Im having a hard time with some of the ideas being presented of ways to make a PVC tank less dangerous by wrapping it with nets or tape or wire

that seems like a seat of the pants kinda thing to do. You would have to test the end product many times to see whether it contained all the little pieces, or whether it made things worse. You would have to repeatedly blow up PVC tanks in a controlled environment, and find a way to measure the energy of the resulting fragments. (Sound like a job for the MythBusters!)

And dont forget the concussion if it blows in a small area. It doesnt take much of a bang to permanently destroy your hearing.

This reminds me of people who put an X of tape across their windows or sheets of plywood, when a cat 5 hurricane is coming. When they return their house is completely gone!

[Nitroxextreme]

If an type of pressurized system blows in close proximity to your ears....ouch

[dtengineering]

We have had some luck with building a PVC water balloon cannon. I only let the students take it up to about 75 psi until well after they had graduated and were "responsible" for their own safety. We took it up to about 90-100 psi for a couple of shots, then destroyed it before fatigue (or cockiness) could set in. Your mileage may vary, compressed air is inherently dangerous and we took appropriate safety precautions.

The book "Backyard Ballistics" describes a pneumatic petard that was the basis for our design. I do recommend a video on youtube, however, http://www.youtube.com/watch?v=_zxlFoZhOC4 to illustrate both the majesty and power of compressed air.

Jason

[FourPenguins]

Originally Posted by KenWittlief

Im having a hard time with some of the ideas being presented of ways to make a PVC tank less dangerous by wrapping it with nets or tape or wire

that seems like a seat of the pants kinda thing to do. You would have to test the end product many times to see whether it contained all the little pieces, or whether it made things worse. You would have to repeatedly blow up PVC tanks in a controlled environment, and find a way to measure the energy of the resulting fragments. (Sound like a job for the MythBusters!)

And dont forget the concussion if it blows in a small area. It doesnt take much of a bang to permanently destroy your hearing.

This reminds me of people who put an X of tape across their windows or sheets of plywood, when a cat 5 hurricane is coming. When they return their house is completely gone!

I'm definitely not advocating PVC tanks. I'm just saying that if you're going to be an idiot, please be slightly less of an idiot.

[Donut]

A question on the irrigation valve; we've gotten it to open by applying power on the relay forward, do you need to apply reverse power to close it or just turn off the forward part?

[Andrew Blair]

The valve will close when power is removed. The solenoid is only used to open the valve- the return spring closes it.

[RyanN]

Originally Posted by Andrew Schuetze

When I get a bit more time, I'll add links to the various threads on C.D. on this topic.

My question is how / where does one get a definitive answer as to the pneumatic pressure rating of schedule 40 PVC? I was intrigued by the team fusion air canon last year and then decided to add one to our 2005 robot this August. I'll post a picture of the prototype mounted on my classroom workbench. It works okay. Based upon three weeks of development, what I perceive to be limiting the performance is the restriction of air flow from the storage tank via the 0.5 inch fitting. Everything else is the same 1" diameter as the sprinkler valve and then expands to the 3" diameter at the back of the muzzle.
I've seen about three cannon systems which are using PVC pipe as the pressurized air storage system here on C.D. People have commented that PVC pressure ratings are for water systems and in fact the fine print at the store indicates use for water only.

My fear is that a bump into a doorway or drop on the floor may start a crack in the PVC pipe and eventual lead to catastrophic failure.

How do I know if I am being overly cautious or just being prudent?

APS


Toltech prototype

We use 60 PSI and we can shoot quite far, so we don't use any crazy pressures like many people are assuming. At most we have put 90PSI in when we were trying to shoot a croquet ball across the football field, but no one was in the stands or the field. Also, we use some type of PVC sleave in the middle of the cannont to prevent it from expanding too much. Just a suggestion, if you get a sprinkler valve that is rated at 24 volts, don't run it in series with a spike. The spike leaks enough current to keep the valve on after releasing your firing button, and it will not work right with only 12 volts. We use 3 9V batteries in series going through a relay connected to a spike and it works well for us.

[Kaizer007]

We have successfully completed building our robotic air cannon. (We converted our 2005 robot) Donut might get some pictures uploaded on here later. We used a blue seven gallon air tank for storage. I'll get the specs to you all later and how we built it.

[Doug G]

Originally Posted by RyanN

Just a suggestion, if you get a sprinkler valve that is rated at 24 volts, don't run it in series with a spike. The spike leaks enough current to keep the valve on after releasing your firing button, and it will not work right with only 12 volts. We use 3 9V batteries in series going through a relay connected to a spike and it works well for us.

We are using a 24 Volt Sprinkler valve, and we thought about how to hook it up to the spikes or a separate battery source like the 3 9V option. But then we tried making it work with just the 12 Volts - and walla... no problem. we've been running this way for the past year. Also polarity (forward or reverse) doesn't matter on most these sprinkler valve solenoids as most of them are meant for 24 V AC. We've switched polarity on ours and had the same results.