optical interrupt for rate of fire.

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unknown_entity
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optical interrupt for rate of fire.

Post by unknown_entity » Mon Jun 30, 2003 6:27 pm

I plan on using an IR or bright red LED with a Photo transistor to make a rate of fire meter for my paintball gun. <p>
Ive got the basic idea and a schematic but does anyone know what the radioshack photo transistors would be most sensitive to red or IR light? <p>I'm actually cheating on this project by hooking the output of the photo transistor to my multimeter that does Frequency.<p>
Any idea on how to make a chrono that will do ball speed short of using radar. Maybe 2 sensors 1 foot apart and multiply the time delay between the two by some factor to get feet per sec?

Chris Foley
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Re: optical interrupt for rate of fire.

Post by Chris Foley » Mon Jun 30, 2003 8:38 pm

If you can get the paintball gun to trigger from an electrical signal, all you have to do is synchronize the firing with a strobe light, and you can determine speed by measuring distance between images. Place a yardstick on the wall behind the paintball's line of travel. Strobotachs can be set at a reasonable speed, and the persistence of vision will allow you to see two images a measurable distance apart. You can plug and chug to determine paintball speed.

rshayes
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Re: optical interrupt for rate of fire.

Post by rshayes » Tue Jul 01, 2003 12:23 am

This is similar to an old physics lab experiment to determine the speed of a bullet. The sensors were two fine wires spaced a known distance apart. The first wire shorted a capacitor. The second wire was in series with a charging resistor. When the first wire broke, the capacitor began charging through the charging resistor. Breaking the second wire stopped the charging process and left a charge on the capacitor proportional to the time of flight.<p>The capacitor was discharged through a ballistic galvanometer to measure the charge. This is a fair amount of trouble, and probably not the way to do it these days. The galvanometer was bolted to the wall and used a reflected light beam as an indicator. You also had to wait for it to stop shaking after firing the gun.<p>A good quality capacitor of about 10 microfarad might be usable with a 10 megohm digital voltmeter. This would give a time constant of about 100 seconds, so there should be little error if the voltage is read within 4 or 5 seconds. Electrolytic capacitors may have too much leakage, but a mylar or polypropylene capacitor should be good enough. Parallel several if necessary. Remember that a digital meter may have to process several samples before it gives an accurate reading.<p>If you have a frequency counter with a period function, this could be used directly without charging a capacitor.<p>An even older method of measuring bullet velocity is the ballistic pendulum, where the vertical motion of a pendulum is noted, the kinetic energy is calculated, and then the velocity is calculated knowing the mass of the bullet. This can be done with crude equipment, but it is a little tedious to set up.<p>[ July 01, 2003: Message edited by: stephen ]</p>

Chris Foley
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Re: optical interrupt for rate of fire.

Post by Chris Foley » Tue Jul 01, 2003 4:52 pm

The business with the two wires is a great idea, if your aim is good enough, and the wires are thin enough so as not to deflect the paintball or slow it down significantly. Use two taut 42 gauge magnet wires, with one end connected to ground, and the other connected to a 1K pullup resistor, Connect both pullup inputs to an XOR gate, which will be high only when one input is high and the other low. If you've got the equipment, you can input that signal directly into a frequency counter with period input. If not, you can AND the signal with the output from a 1MHz crystal oscillator package with TTL output, and count the microseconds digitally. After that, again, plug and chug, with a known distance.<p>This is actually a better idea than the strobotach, because paintballs ain't cheap, you can't catch 'em, and they're pretty messy. I could see letting loose a volley of a hundred paintballs in a dark room, and chalking marks on the wall in the interests of science. What I couldn't see is what the room would look like when you turn on the lights. :0)

unknown_entity
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Re: optical interrupt for rate of fire.

Post by unknown_entity » Tue Jul 01, 2003 6:48 pm

Image<p>Image
http://www.tippmann.com/markers/default.asp
Yeah all that and full auto. I really dont care about measuring the speed because all the fields have chronos. I just wanted a quick way to tell rate of fire. Im guessing 18 per secong give or take a couple.<p>ill just make the rate of fire this weekend and let you know how it works out.<p>[ July 01, 2003: Message edited by: unknown_entity ]</p>

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