FIRST air cannon robots PVC??

[ChuckDickerson]

Originally Posted by KenWittlief

Id recommend one of those portable tire air tanks you can get at Walmart for $60 or so. The ones you fill up at a gas station with compressed air. They are tested well above their rated pressure (rated at 120psi?), and they are steel, so if you drop one the seams wont burst open.

Another real cheap and SAFE option is to make your own steel air tank using an old freon tank. Go to a local HVAC service place and ask them for and empty freon tank. They always have one and you can probably get it for free. Then head to your local auto parts store and get a Freon tank conversion kit like this: http://www.redboxtools.com/detail.cfm?productID=1616. I have bought kits like this locally at NAPA for ~$10 but haven't bought one in a while. You just screw the adapter on the existing fitting on the freon tank and bam, instant safe steel pressure tested air storage tank. Freon tanks come in a couple of different sizes so if you prefer get a small one for the robot. Paint the tank to suit you needs.

BTW: My office is in a building next to a wet lab. The wet lab needs compressed air. Nobody wanted the air compressor near their office because of the noise so they installed the compressor out behind the building and ran the air feed line through the ceiling of the building right over my office to the lab. The installers used 3/4" PVC for the air line which is pressurized to about 120 PSI most of the time. I voiced my concerns to the installers about using PVC rather than some other pipe like copper tubing or black pipe or something and they said "don't worry about it, it is fine, we do it all the time, the side of the pipe says 600 PSI" or something like that. So far, the pipe hasn't blown up over my head but I still worry about it. I don't know why but I still have visions of the pipe exploding and showering me with a million little shards of white plastic one day.

[Dan Richardson]

Often plummers that need to run pvc on the oustide the house will cover the pvc coat the pvc with some sort of plastic polymer. The reason being is so that the pvc is not as exposed to the sun. Additional reason it adds additional support.

But the glue/resin as some have pointed out is important. I remember the "blue" pvc glue was rated for something like 180-200 psi max operating pressure.

When applying pvc glue make sure you are careful to first clean the ends of your pipe that you are applying. Bevel the edges slightly with paper or a file. Then proceed to place a thin layer on both the inside of the cap and the pvc you are using. When insert turn the pvc slightly, about a little less than a quarter of a turn.

Most important is beveling the edges and applying to both sides, often when cutting the pvc it becomes very sharp and jagged. There is often a lip on the edge and when inserting into a connector the bevel can push the glue out. So instead of an even gluing you have it bunched in certain spots. Not good for adhesive properties.

[Donut]

Another easy alternative to using the PVC for storage is to use the storage tanks FIRST gives in the kit (and if you've been around for a few years, you've probably accumulated a few of them).

Our team is developing a cannon that uses almost nothing but KOP pneumatics, with the exception being our barrel and its mount.

One question regarding the Festo Single Solenoid valves; where is the documentation for the maximum operating PSI? The FIRST documents only list the minimum, and I cannot find the specs sheet for it through google or on Festo's site.

[Doug G]

Originally Posted by Donut

Another easy alternative to using the PVC for storage is to use the storage tanks FIRST gives in the kit (and if you've been around for a few years, you've probably accumulated a few of them).

Our team is developing a cannon that uses almost nothing but KOP pneumatics, with the exception being our barrel and its mount.

One question regarding the Festo Single Solenoid valves; where is the documentation for the maximum operating PSI? The FIRST documents only list the minimum, and I cannot find the specs sheet for it through google or on Festo's site.

This depends on the size and length of your barrel. Our team's CanonBot uses a 3" Barrel, 3 feet long. At first we tried the Festo valve at 60 psi, but there's just too much restriction for our application. The sprinkler valve seemed to work the best for us. We use 2 steel tanks which lead to a manual ball valve which acts as our safety. After the ball valve is the sprinkler valve and then to the barrel. We keep safety valve closed except when the robot is in operation and everyone is clear of the robot and the barrel. We usually run our pressure between 60 and 80 psi.

[Donut]

We're planning on using 2 or 4 Festos in parallel, we want to see how much can be done with using mainly FIRST parts.

I think there may have to start being "cannon contests" at off season events with how many of these are being built.

[KenWittlief]

I would look into using a pnuematic cylinder, with a mechanical trigger

if you try to use a cylinder to launch stuff the airflow into the cylinder is too restricted by the small connectors and hoses

to fix that, you put a mechanical stop, about half way down the cylinders travel, that holds the pressurized piston back

to fire the launcher you pressurize the cylinder against the trigger/ release pin, then you pull the pin out of the way, allowing the cylinder to extend all the way

in effect you have a large pnuematic spring.

I think you will find this takes much less air, than blowing Tee shirts and stuff out the end of a PVC tube. Also the thing you are launching does not have to fit snugly into the tube, you could put just about anything in there.

The plus for safety is you can build this will all standard (approved) pnuematic parts and valves, you wont have to worry about pressurized PVC failing in a room with thousand of people around.

It can still be made to look like a cannon, in fact you could release CO2 or smoke to make it look more omminous. Only you would know whats really happening inside.

[Billfred]

Originally Posted by KenWittlief

I would look into using a pnuematic cylinder, with a mechanical trigger

if you try to use a cylinder to launch stuff the airflow into the cylinder is too restricted by the small connectors and hoses

to fix that, you put a mechanical stop, about half way down the cylinders travel, that holds the pressurized piston back

to fire the launcher you pressurize the cylinder against the trigger/ release pin, then you pull the pin out of the way, allowing the cylinder to extend all the way

in effect you have a large pnuematic spring.

I think you will find this takes much less air, than blowing Tee shirts and stuff out the end of a PVC tube. Also the thing you are launching does not have to fit snugly into the tube, you could put just about anything in there.

The plus for safety is you can build this will all standard (approved) pnuematic parts and valves, you wont have to worry about pressurized PVC failing in a room with thousand of people around.

It can still be made to look like a cannon, in fact you could release CO2 or smoke to make it look more omminous. Only you would know whats really happening inside.

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).

[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.