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AP Physics Project

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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AP Physics Project

Unread postAuthor: Sabercat » Sun Aug 31, 2014 9:18 pm

My mission is to build a launcher that will launch a tennis ball into a basket. The basket will be placed at 3 different distances of 3.0, 5.0, and 10.0 meters from my launcher. My launcher must be free standing. I will not be allowed to support your launcher off the ground as I launch. Combustion may NOT be used :evil: . Here are the requirements for compressed air. The holding tank for the compressed air may not exceed 2 feet in length and 3 inches in diameter. No more than 60 PSI may be used for launch. (In theory, how far will this shoot based on your experience?) All materials used must have a pressure rating of greater than 100 PSI (Easy). The labels on the materials must be visible upon inspection. All junctions must be sealed per construction standards (i.e., PVC joints will be inspected for proper primer, glue and proper seal.). How do I seal the "Schrader Valve?" The holding tank must have a pressure gauge on it so that the instructor can ensure that the PSI limits are not exceeded and that the tank has no leaks. Keep in mind that this is for a tennis ball.

Thank You So Much For Your Help!
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I want it to look like this, (or similar) but it has to have a stand.

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Re: AP Physics Project

Unread postAuthor: jrrdw » Mon Sep 01, 2014 9:08 am

You made no mention of firing valve...Any restrictions on that? You can use a metal Schrader valve, they are threaded just use teflon tape to seal the threads and placement should be through double thickness PVC area.

2X4s and plywood for a stand with some adjustability build in for aiming.

Plenty of ideas here on the forums to look through...
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Re: AP Physics Project

Unread postAuthor: Sabercat » Mon Sep 01, 2014 9:42 am

What is you recommendation for the valve from the air chamber to the barrel? I need something that is consistent because we are running 3 trials for each target. And the accuracy is our grade.
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Re: AP Physics Project

Unread postAuthor: noname » Mon Sep 01, 2014 10:26 am

I could see a tennis ball getting chucked ~50 meters by those specifications. Getting a consistent valve that will seal at 5 or 10 psi will be the trick since that 3 meter shot sounds tricky.
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Re: AP Physics Project

Unread postAuthor: sagthegreat » Mon Sep 01, 2014 12:00 pm

noname wrote:I could see a tennis ball getting chucked ~50 meters by those specifications. Getting a consistent valve that will seal at 5 or 10 psi will be the trick since that 3 meter shot sounds tricky.



He may be better off trying to find burst disks that will burst at the pressure needed to get those distances
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Re: AP Physics Project

Unread postAuthor: jrrdw » Mon Sep 01, 2014 12:56 pm

Sabercat wrote:What is you recommendation for the valve from the air chamber to the barrel? I need something that is consistent because we are running 3 trials for each target. And the accuracy is our grade.


noname wrote:Getting a consistent valve that will seal at 5 or 10 psi will be the trick since that 3 meter shot sounds tricky.


Spring loaded ball valve. Lube it up to make it turn easy.
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Re: AP Physics Project

Unread postAuthor: Technician1002 » Mon Sep 01, 2014 3:58 pm

sagthegreat wrote:
He may be better off trying to find burst disks that will burst at the pressure needed to get those distances


Getting a burst disk calibrated for a repeatable distance is a problem.

Question, is launcher modifications permitted between shots for different distances? If yes, instead of a burst disk, a union contaning a hand crafted throttle restriction plate would provide very consistant launches at a fixed pressure high enough for reliable sprinkler valve operation. Remember that repeatability is key. Elemination of variables is critical such as various pressure, valve response (hand turned ball valve) etc.

Start with a blank metal plate cut to fit in a union to block the flow and drill 3/8th inch holes and test your distance on ~40PSI. If close to one of the target distances, trim the distance by adjusting the pressure. Place the flow restriciton between your valve and barrel, not the tank and valve. Change hole sizes and number to get consistant shots for your distances at ~40PSI. Fine tune with pressure regulation. Good Luck.

The short close shots can be the hardest.

Here is an air cannon lob of a golf ball into a wheelbarrow. Distance was perfect. Aim was slightly off and hit the side. This is one of my videos. 10 yard shot inside a 1 sq yard target.

A very repeatable performance valve is a requirement.
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Re: AP Physics Project

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Re: AP Physics Project

Unread postAuthor: Sabercat » Mon Sep 01, 2014 6:32 pm

Ok, so I have decided to use a sprinkler solenoid valve to let the air pressure out of the air chamber. Can someone tell me how I would make this work? With batteries & wiring. And is this even possible?
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Re: AP Physics Project

Unread postAuthor: Technician1002 » Mon Sep 01, 2014 10:18 pm

A 24VAC sprinkler valve is easly operated on 18VDC using 2 9 volt batteries in series. The reason it works is due to the impedance of the solonoid vs DC resistance. The current is actually higher on 18VDC than it is on 24VAC, so it has no problem operating. Use this for intermittant use only. Continous operation on 18VDC will let the magic smoke out.

For wiring, connect the + of one battery to the - of the other to place them in series. Connect a pushbutton to the free + wire such as a door bell button. Connect the other wire of the doorbell button to one of the valve wires. Connect the other valve wire to the remaiing - wire of the two batteries. Everything then should be daisy chained together in a big circle with no more than two wires connected at any one connection. Push the button and the valve operates.

For a tennis ball launcher, 1 inch should be the minimum valve and plumbing size to consider. 1.5 inch is even better. 2 inch becomes hard to find and expensive. Don't bother. It is better to be oversize and dial back then undersize and unable to reach your target.
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Re: AP Physics Project

Unread postAuthor: jimmy101 » Sun Sep 07, 2014 6:10 pm

A smaller sprinkler valve might be better. Since your max range is pretty short, only about 30 feet, you really shouldn't need the much more expensive 1" or greater valve. Heck you can underhand lob a tennis ball 30' without any problem. Usually though when people build a cannon they want to launch something considerably farther than they can throw the object.

Download GGDT (Gas Gun Design Tool) and play with your dimensions, pressure etc. I would design the gun so the 10 meter shot is nearly the maximum the cannon can do. That way you might be able to do the shorter shots just by changing the launch angle (if that is allowed) or by lowering the chamber pressure if you have to use a fixed launch angle.

GGDT is at http://www.thehalls-in-bfe.com/GGDT/
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