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Digital Pressure Switchs?

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Digital Pressure Switchs?

Unread postAuthor: THUNDERLORD » Mon Apr 21, 2008 12:05 am

I had one main thought today about constant factors which could be used in design for spud type technology those are:
1---Pressure : All launchers have that in common (Self explanatory)

2--- Movement : Whether it's the bolt or the projectile itself.

I am thinking these two factors can be used for initiating other events/ timing things more simply.(For myself mainly w/ the JSR bolt)

Also I am fascinated by the blow forward bolt design of JSR and clide's GB semi.

Also,Some of you may be aware of a component I call a "thunderswitch"
It basically uses the pressure factor to close a switch to initiate valves or other electric devices electrically.(A jerry rigged dial gauge version pressure switch).

The other factor I stated (Movement) Is simpler because a moving part closes a switch. (Although that part is probably moving due to pressure) I have catagorized it seperately to simplify the design wherever possible.

I would like to simplify my "thunderswitch" further by making it digital.

My question is on that (but this post is about other constant factor of movement as well), The only circuit I can think of commonly would be a digital thermostat.
The whole thermostat concept reminds me of what I am trying to accomplish.

The old fashioned thermostat used a bi-metal strip. The two metals expanded differently causing it to physically move and the mercury switch activate. The newer models use digital thermometers and switching. Any comments are welcome!!!
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Unread postAuthor: Blitz » Mon Apr 21, 2008 12:40 am

It sounds like you want to make your own pressure switch. They already exist, if it works for you.

When you say pressure switches, you're referring to these, right? These are designed specifically to actuate at a particular pressure.
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Unread postAuthor: THUNDERLORD » Mon Apr 21, 2008 1:03 am

Thank you very much for the link Blitz. Back when I dreamed up rigging a dial gauge to work as a switch I didn't know if a suitable one was even made or would be affordable.

Also there were almost no examples of home made semi auto and few repeaters even to look at.

Maybe I should have worded my actual question like Is there a way to hack up a house-hold type digital thermostat for use in pneumatics?
Similar to how people make coilgun parts from disposable camera flash circuits.

The number on the thermostat is preset and when that number is reached the thermostat triggers switchs. and it is done digitally.
Maybe one of the electronics guys could come up with a schematic for a way to use similar switching on a digital pressure gauge?

Another purpose of this post was to think of basic laws of launchers?
I have determined two: pressure and movement.

By using the constant factor of movement, the both versions of pressure switchs (mine and factory made) could be eliminated anyway though.
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Unread postAuthor: Blitz » Mon Apr 21, 2008 1:50 am

Well, don't forget those thermostats are actuating to temperature differences, not pressure differences. :) I'm not completely sure a thermostat would be suitable in any way, but my knowledge of electronics is basic at best. I'm lucky to be able to wire up my own ignition system for my own cannon!
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 21, 2008 2:00 am

It would be fairly easy to make your own on/off pressure switch by using a spring loaded sealed plunger, operating pressure could be varied by altering spring strength.
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Unread postAuthor: Blitz » Mon Apr 21, 2008 2:06 am

There you are! Where've you been? :)

So basically, find out which tensions actuate at a particular pressure by trial-and-error? Or some of the more well-versed in the way of physics can actually calculate that? (I'm sure it's somewhat possible)
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Unread postAuthor: THUNDERLORD » Mon Apr 21, 2008 2:19 am

jackssmirkingrevenge wrote:It would be fairly easy to make your own on/off pressure switch by using a spring loaded sealed plunger, operating pressure could be varied by altering spring strength.


YEAH!!! AHA!!! I was kind of hoping that if I made a reference and gave you proper respect, that you'd reply too. And it worked!!!(Except I just got bumped offline by the server)

Hello JSR, Great to converse with you, What you said here exactly I was thinking except you see the "spring loaded sealed plunger" could be the actual bolt in your blow forward bolt design. Somehow I think you already knew that, but aren't interested in electronics use.

EDIT: Also with the thermostat circuit I was wondering if the read out of a digital gauge like for tires could somehow replace the read out/ input of the thermostat, that way instead of working by temperature it would work by pressure (and be adjustable)?
EDIT2:Geez I am tired from work, I got all carried away about the way thermostats maintain a set number and are adjustable and totally forgot clocks are digital and programable too. Just need to input the digital gauge # instead of alarm time somehow?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 21, 2008 3:52 am

I can picture an electrically triggered solenoid valve that opens only when the bolt is in the "open" position (ie ammo can fall into the barrel) allowing a puls of air to work the bolt, though the issue seems to be how long it would take the valve to reseal once the solenoid is no longer operating-
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Unread postAuthor: jimmy101 » Mon Apr 21, 2008 12:48 pm

It depends a lot on what time domain you are trying to sense the pressure. If it is a slow domain, as in controlling the cycling of the gun, then you could rig up an adjustable pressure sensor from a cheapo tire pressure gauge.

A snap-action switch, or a slot opto isolator, or a home brew opto isolator, or add a small magnet to the gauge and use a Hall affect switch.

Since tire pressure gauges are peak recording gauges you'll have to modify the gauge so the scale is attached to the internal piston. A glob of epoxy should work.

A slot opto isolator has an led and a light sensor separated by a small gap;
Image

http://www.allelectronics.com is a good source for optos, switches etc.
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Attachments
pressure_sens.gif
hacking a tire pressure gauge into an electrical switch.
pressure_sens.gif (4.44 KiB) Viewed 812 times
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Typical snap-action switch
SMS-228.jpg (22.17 KiB) Viewed 812 times
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Unread postAuthor: THUNDERLORD » Mon Apr 21, 2008 10:45 pm

@ jimmy101, awesome that you replied, It's funny that you're the exact electronics person I was thinking of maybe posting a schematic after I read your reply (w/ capacitor schematic) in the thread about a washing machine solenoid. Man spudfiles is cool!!!

Anyway, I have a switch just like one example you posted it. With very light pressure it clicks on. Also I posted the stick type tire gauge in one of my first posts entitled "valve initiators" I got some stupid replies and I was thinking any way that the gauges on tire gauges like that are always inacurate. But it is a variation of the "thunderswitch" as I call it. (It's cool to name components after yourself a little but that's just what I call them.
I am considering using an end cap (the one shaped like a smoking pipe)
with that type gauge (w/the head removed and a piece of rubber and a hose clamp then epoxied in) for a low pressure sprinkler valve launcher.

Thankyou very much for the reply jimmy101, I sometimes leave out eye candy on purpose or give long winded statements for certain reasons btw.

Imagine a top quality pcp rifle with a small rectangular window in the stock and watch sized buttons that can be programmed with the pellet type and velocity you want and it adjusts itself from there!!!

That would be one application (for example)and you yourself could design it and make some $(bucks)
Also a Firearm can only accomplish that through handloading.

@ JSR, Back to the drawing board for me, I was very let down about the facts you stated about the reclosing of solenoid valves.
My whole auto refill system needs to be redesigned.

Once again you saved me a lot of time. well if you reply back I will describe better. Thanks and anyone elses' replies are welcome!!!
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