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Thread: All-electric simulated machine gun?

  1. #11
    rwanttaja's Avatar
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    Quote Originally Posted by danielfindling View Post
    An Arduino micro controller would seem appropriate for the project as well. The flashing LED is simple code and a MIDI file for the sound. . .
    Oh, you gol-darn kids...having to put a microprocessor in everything. I swear, it makes me want to disassemble a rotary switch to control the light, with up a key-wound clockwork mechanism to turn the switch and make the light flash.

    And get off my lawn!

    Actually, we *might* have to go with a microprocessor, for one key point: Synchronizing the flash with the bang. Everything we talked about so far treats the light show and the audio show separately. Sure, Einstein and Mach make sure the flash reaches the eye before the bang hits the ear....but if the visual is going FlashFlashFlashFlash and the audio is going bang....bang...bang...bang... well, heck, that's just gonna be weird. Could adjust the flash circuit to match the rate of the audio file, but there's a good reason to automatically synchronize them (I'll get to it in a bit).

    However, there's another realism point to consider: What you hear from a gun three feet away is NOT what you'll hear from a gun a hundred feet away. A close-in recording is going to get the sound of the gun's action moving, the bolt slamming shut, the belt sliding, and the brass hitting the ground. Playing that recording with a big *** amplifier is going to amplify these ancillary noises, too, and again, that'll be unrealistic. So a recording of a Lewis, Vickers, or Spandau may not be the way to go.

    The *right* sound would be a *single shot* from a bolt-action rifle, repeated electronically. Bolt-action, so there's no mechanism noise involved. You'd take that noise, and repeat it. For one thing, that'll let you fire a burst of unlimited length. Most of the recordings probably are of the approved short-burst variety. Just re-starting the short-burst MP3 will also be weird.

    Repeating the sound would be easy, but properly synchronizing it with the flash might not be. A simple microprocessor may not be able to play an MP3 file simultaneously with toggling an output line.

    All right: Here's why I want the noise and light to automatically sync up: I visited the Historic Aircraft Restoration Museum in Creve Coeur, Missouri last fall. They've got a replica Sopwith Pup, with not only an original LeRhone engine, but an operable Vickers machine gun with a working interrupter gear. Our guide had actually flown the Pup with live ammo. He pointed out that the rate of fire of the Vickers *depends on the speed of the engine*.... That at low RPMs, the gun could put out more bullets before the prop blade intervened. So if you dive the plane, the gun shoots slower...and starts shooting faster as you pitch up and start climbing.

    And if you have the audio automatically syncing with the flash in our simulator, you could vary the firing rate by airspeed.....

    Ron Wanttaja

  2. #12
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    OK, in that case I vote that we get someone to record a 7.62x54R Mosin-Nagant, preferably one of the short carbine versions, as they make the most impressive boom and muzzle flash of any standard-caliber bolt-action I have seen.

    Seriously, I do get your point and I agree that a recording right next to the gun might pick up wanted mechanical noise, but if the microphone is a few yards away I don't think it will matter. Regardless, sample recordings of the real guns would give confirmation of the rate of fire in actual use and a point of comparison for how realistic the simulation sounds. That said, you may well be right that recording just a single shot and looping it in synch with the light would be the easiest solution.
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  3. #13
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    Here is a nice sound clip of a Vickers: http://m.youtube.com/watch?v=hPv_f_aSyP4

    Lewis machine gun: http://m.youtube.com/watch?v=hPv_f_aSyP4

    Spandau machine gun: http://m.youtube.com/watch?v=hPv_f_aSyP4

  4. #14
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    Quote Originally Posted by rwanttaja View Post
    Mentioned this project at EAA Chapter 26 last Thursday, and one of the members put me on to a local electronics store that carries a bunch of high-intensity LEDs. Bought a 5W unit that runs on 12V. They had a 10W unit, but it needed 30VDC and I figured you didn't want to pack 20 AA cells. :-)

    Got some other goodies with which I hope to gimmick up a flasher. Perhaps by next weekend I'll be able to post a video showing the daylight visibility over a distance.

    A local Boredom Fighter builder named Bill Sayre has been monitoring this conversation, and sent me some pictures of his dummy Vickers guns....Bill also sent me the schematic he used for the flasher circuit. It appears to mess with the control input of a standard voltage regulator chip. This works on Bill's incandescent bulbs, but I don't know if it'll work on a high-intensity LED. In the immortal words of Commander Montgomery Scott, "I'll let ye know."
    Attachment 2798

    Ron Wanttaja
    I built the circuit last night, didn't seem to work right with the high-intensity LED. I suspect that the timing is thrown off by using the LED vs. an incandescent bulb. The power draw is probably way less, and incandescent bulbs are somewhat self-regulating.

    No matter. I'll rig up a 555 and use the LM317 as a switch for the LED (don't think the 555 can drive a 5W device directly).

    Ron Wanttaja

  5. #15

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    Quote Originally Posted by danielfindling View Post
    Here is a link on a gas powered machine gun. (Oh, I am looking for Lewis Machine Gun parts - anyone?)

    http://www.kcdawnpatrol.org/machine-gun.htm
    For a good, inexpensive "stand off" replica - http://www.foxflier.com/lewis/ - including some examples that were turned to gas powered. I'd show you pics of my 7/8th scale one, but it's not assembled yet.

    I always thought that if I were to go the 'lectric route to make it fire, I'd put the speaker behind the seat and let the empty rear of the fabric covered aircraft act like a big sounding drum to amplify it.
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  6. #16
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    I did some digging and what might work here is a "color organ" or "light organ" circuit for synchronizing lights with music, though you want one specifically for LEDs and 12v not for incandescent lighting and the home stereo system. Most are multi-channel -- here's an example including a link to instructions and a circuit diagram -- but it sounds like Ron or others would have no trouble understanding the circuit diagrams and creating a simplified, single-channel version for the machine gun flash.

    If someone is looking for a project, it might be worth making the multichannel example in the link and then testing it to decide which frequency response works best for this application. The input would come directly from the speaker feed, which would solve any synchronization issues.

    The next step would be to rig up a cheap way to feed the speaker with a looped recording of a single rifle shot as has been discussed. A simple loop would work, but for best sound, I think it would be great if the shots could be overlayed like this, with the next shot firing over the continuing reverberation of the previous one, if you see what I mean:

    BANG - r e v e r b e r a t i o n
    __________BANG - r e v e r b e r a t i o n
    ____________________BANG - r e v e r b e r a t i o n

    Cheers,

    Matthew
    Last edited by cluttonfred; 02-22-2013 at 01:16 AM.
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  7. #17
    rwanttaja's Avatar
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    Quote Originally Posted by Matthew Long View Post
    I did some digging and what might work here is a "color organ" or "light organ" circuit for synchronizing lights with music, though you want one specifically for LEDs and 12v not for incandescent lighting and the home stereo system. Most are multi-channel -- here's an example including a link to instructions and a circuit diagram -- but it sounds like Ron or others would have no trouble understanding the circuit diagrams and creating a simplified, single-channel version for the machine gun flash.

    If someone is looking for a project, it might be worth making the multichannel example in the link and then testing it to decide which frequency response works best for this application. The input would come directly from the speaker feed, which would solve any synchronization issues.
    I agree the flash should be triggered by the bang....and considering the size of the bang we hope to issue, triggering shouldn't be any problem. The main trouble is, the flash is basically binary...it's on or it's off. We're talking about wave-shaping the bang, but the flash is going to be pretty simple in comparison.

    The organ circuit takes the music input, and runs it through low-pass, band-pass, and high-pass filters, with each filter turning on a bank of particularly-colored LEDs when a threshold is reached. The organ circuit has the right idea...but we'd end up needing multiple high-intensity LEDs to try to implement it. It's going to be tough enough to have one LED bank bright enough to be visible 500 feet away on a sunny day; packing in three or more is going to look really funny. Plus, the closer it gets, the more obvious the flashes are coming from slightly different positions.

    What would be nice is if we could input a waveform to the LED and have it track it by *brightness*. An initial high-intensity, dropping off over the next quarter-second or so. Doable (especially if we end up with a microprocessor anyway), but it is getting a bit complex.

    If brightness weren't an issue, I'd install a big LED at the muzzle and a trail of additional ones leading forward. Do the big flash, then sequentially zip through the others real fast.

    Quote Originally Posted by Matthew Long View Post
    The next step would be to rig up a cheap way to feed the speaker with a looped recording of a single rifle shot as has been discussed. A simple loop would work, but for best sound, I think it would be great if the shots could be overlayed like this, with the next shot firing over the continuing reverberation of the previous one, if you see what I mean:

    BANG - r e v e r b e r a t i o n
    __________BANG - r e v e r b e r a t i o n
    ____________________BANG - r e v e r b e r a t i o n
    I'm not sure how much reverb would be present; again, not only are the listeners going to be hundreds of feet from the gun, but the gun itself is going to be well off the ground. I found the following spectrum of a gunshot online:
    Name:  bang.jpg
Views: 1087
Size:  49.7 KB
    I'm guessing the initial sound pulse is the shot itself, probably the "slap" of the air compressed by the passage of the bullet (and possibly a supersonic shock wave). Note the incredibly short time duration, and the high amplitude compared to the rest of the waveform. Following up 8 milliseconds later is a reflected shock wave (probably an environmental effect we can ignore).

    About 15 ms after the first shock is the muzzle blast...probably the "reverb" effect we're looking for. Note, though, how much lower the amplitude is.

    It's my contention that the muzzle-blast effect would be severely attenuated by the time it would reach an observer 500 feet away. Hence, we should be primarily interested in reproducing the initial "pop."

    Remember that the pop is massive. Hearing protection would be a must if your sound system actually reproduces the sound of the gun, at least in close proximity.

    This reproduction has its problems (like most, I guess :-). If you want to SOUND like a gun firing, you need to move the same amount of air at the same speed, within the same short span of time, with amplitudes so high that you need earplugs. If we say that spike is on the order of ~0.2 ms wide, that needs a speaker with decent a frequency response of 5000 hz. So we have two conflicting requirements... we need to move a LOT of air (we need a big woofer!) at a fairly high frequency (we need a tweeter, which generally don't push large masses of air).

    Most of us have probably been present when a gun is fired. And we all realize that they don't SOUND like the guns we hear in movies and TV. Hollywood can't reproduce the pop, which is the major sound component. I live a quarter-mile from a police gun range, and when it's active, all I hear is a series of pops.

    But...and this part makes me giggle, just a little bit... maybe we DON'T want to be real. Most people are accustomed to Hollywood gun sounds, and that's what they'll expect. Let's give them "Bang chugaluggalugga Bang chugaluggalugga" or whatever sounds like Sylvester Stallone.

    Seems to me that microprocessor should be able mix two overlapping waves of the same sound so the reverb effect on the first shot can continue through the second. We'd probably want this anyway, for the folks who might install two guns.

    Ron "This is a lot more fun than reading accident reports" Wanttaja
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  8. #18
    rwanttaja's Avatar
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    Quote Originally Posted by rwanttaja View Post
    Remember that the pop is massive. Hearing protection would be a must if your sound system actually reproduces the sound of the gun, at least in close proximity.
    Which reminds me of the importance of another piece of safety equipment: A volume control.

    The local gendarmerie will Not Be Pleased if they get a whole bunch of phone calls from folks claiming there's machine-gun firing coming from the house down the street ("You know, the quiet guy..."). If you're based at a controlled field with airline traffic, you might get an intimate visit from the TSA....

    Ron Wanttaja

  9. #19
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    Well, I do love an experiment.

    I built a simple light-flashing circuit using a 555 timer chip. As it doesn't have enough capacity to directly drive my high-intensity LED (12 v, 5 watt), I added a solid-state NPN power transistor as a switch.

    The problem is, there's an unavoidable voltage drop across the power transistor. I was using the an old Odyssey battery, which was down to 11.5 volts. With the ~1.5 v drop across the transistor, the high-intensity LED was only getting 10V. From ~150 feet away outside, it really wasn't that visible. The camera even had trouble picking it up, probably related to the flash rate

    When I connected the LED directly to the battery, it was a LOT brighter, and very visible in daylight.

    One way to get rid of that 1.5 v drop is to use a relay. I had picked up a 12V relay at the local parts store, and wired that in, instead. A quick test shows that it's nice and bright...in the video, a wide swath of the camera pixels are actually saturated.

    http://www.bowersflybaby.com/test_vid.wmv

    So.... a high-intensity LED would probably work. One problem, though, is that the relays are generally not that good for flashing at high speed (simulating a higher rate of fire). So either one has to find a lower-voltage high-intensity LED (so the Power Transistor loss doesn't affect it) or be satisfied with a lower rate of fire.

    Ron Wanttaja

  10. #20
    Dana's Avatar
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    How 'bout a solid state relay? Much faster than a mechanical one.

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