SpudFiles

Hi guys. I have been wanting to build an automated tennis launcher for some time now. I know I could just go out and buy one, but that takes away the fun of building one. I was planning on using an unmodified sprinkler valve as the main valve with the chamber pressure pretty low, so as to not kill anything the tennis ball touches. The problem is, that I wouldn't be able to activate it every time. Is there anything that I can do to make it so a solenoid sprinkler valve will open, close, and then open again 5'ish seconds later? I could have the chamber hooked up to a low power air compressor to constantly fill the chamber. So, any ways of helping me out?

I would actually mod the sprinkler valve and instead of using the solenoid that comes with the sprinkler valve, I would use a three way solenoid valve that both fills the chamber and pilots the sprinkler valve. For the timing, get some sort of delay switch where you can adjust the delay. When it reaches the delay it switches the valve and pilots it.

For loading, I would probably make a blow forward bolt and use either a clip or a hopper.

On second thought, instead of using a three way solenoid, you could use a needle valve or partially opened ball valve to slowly refill the chamber since you have 5 seconds. It would be way cooler though if you used the three way solenoid (faster refill time) and changed the delay switch to a second or something.

Check this site out: http://www.aaroncake.net/circuits/relaytim.asp

Maybe a pressure switch hooked up to an unmodified sprinkler valve circuit, that way when the chamber reaches a certain pressure, the pressure switch completes the circuit, firing a tennis ball, then when the chamber fills back up, it shoots again. You can buy a pressure switch at the spudfiles official store, http://www.bcvids.com/store/product_inf ... ucts_id=62

potatoflinger wrote:Maybe a pressure switch hooked up to an unmodified sprinkler valve circuit, that way when the chamber reaches a certain pressure, the pressure switch completes the circuit, firing a tennis ball, then when the chamber fills back up, it shoots again. You can buy a pressure switch at the spudfiles official store, http://www.bcvids.com/store/product_inf ... ucts_id=62

Or use a QEV and pilot it with a pop off valve.

Modderxtrordanare wrote: Or use a QEV and pilot it with a pop off valve.

That's what I was thinking. Pilot the 1-1.5" sprinkler valve with a 1/2" sprinkler, piloted by a safety pop-off (they come in various pressures, but for your application a 50-75psi sounds about right). This would automatically pilot the valve when it hit the set pressure, then reset (reseal) when the pressure got low enough (right after firing...). You might have to adjust the pressure/flow coming out of the compressor, but I'm sure it could be made to work.

That's the easiest way to do it I can think of.

Peace
Pete Zaria.

doesnt BCarms sell an electronic switch that makes a circuit connection when it hits 100 PSI? just wondering. i think that would work, if you could get one that turned on at a lower pressure......

VH_man wrote:doesnt BCarms sell an electronic switch that makes a circuit connection when it hits 100 PSI? just wondering. i think that would work, if you could get one that turned on at a lower pressure......

You can get saftey pop-off valves at even as low as 60psi, using one of those in place of a blowgun on the sprinkler would fire it every time it hit 60psi. Time the filling right and you could get it to fill slow enough to give you a 5 second delay in between firing.

Hi,

If the original solenoid valve on the spinkler won't do, get a separate solenoid valve and use that to control the modified sprinkler valve. Maybe salvage the water intake valve from an old washing machine, or buy one as a spare. Try to get one that runs on low voltage.

Regards
Soren

You can make it have a delay with a 555 timer circuit.

Here is the design for a 555-based timer:

http://www.kpsec.freeuk.com/projects/timer.htm

Sorry I haven't been able to reply to your replies, I have been away at a camp. I like the ideas and would like to look into them in greater detail. But how fast would a tennis ball go at 60 psi?

<aside>Another one who would fail the IQ test </aside>

3.5 times T

where T is a constant that can be found only once you have built your cannon and tested it, with a tennis ball, with a Chronograph.

(IE there is no way to tell)

Michael

I know that I won't be able to find the exact speed, but roughly how fast will it go? Such as, will it go over 100 fps and so on. Also, if a pop-off valve is used to pilot a QEV, won't the pop-off valve close once the pressure goes below the given pressure rating? I like the 100 psi switch, but is there something that will go off at a lower pressure?

pop off are 115psi aren't they well at least all the ones you don't have to special order of the internet. and they will stay open if the pressure is around the pop off after the pressure has reached the threshold. for example i have an air compressor hooked up to some tanks with a safety pop off i go to 115psi the thing goes off and doesn't close until the pressure goes below 80psi. well at least thats what happens with mine the same problem might not happen at lower pressures. also im sure they sell pressure switches for lower pressure. i swear i saw a 55psi electronic pressure switch on some surplus army supply site a few weeks ago

To fire either a piston or a sprinkler you just need a difference in pressure. The bigger the difference the better the performance. By using a pop-off once it hits whatever psi it'll open and pilot the valve.

It would take a bit work to get it just right I would have though though...

Michael

Thanks for the help guys. I think I am going to try to use a modified sprinkler valve with a pop-off valve as the pilot. Correct me if I am wrong with this process.
1. Air from the compressor fills the chamber to about 60 psi
2. The pop-off valve opens releasing air and piloting the diaphragm inside the sprinkler valve.
3. This air goes into the barrel and pushes out the tennis ball. While this is happening, the pop-off valve closes and the pressure in the sprinkler valve closes it.
4. The air compressor continues to pump air into the chamber, and continues this cycle.

The one part I am confused about is step three. If the air compressor is constantly on, it will always be sending more air into the chamber. Even if the pop-off valve closes, won't the diaphragm in the sprinkler valve be open still be open due to the constant stream of air pushing up against it? If this is true, than can anyone give me some helpful hints or ideas on how to fix it?