Fast rate LED flasher for RC helicopter guns

Discussion in 'General Electronics Chat' started by jim stapenell, May 21, 2009.

  1. jim stapenell

    Thread Starter New Member

    May 21, 2009
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    G'day all - I am building a radio controlled helicopter which is about 1.3 metres in body length. The heli is a model of AirWolf and has machine guns. I would like to build a FAST LED flasher (1 for each gun = 6 total). I have mounted some 3mm LED's into the end of each gun (3 on left hand side and 3 on the right). I have tried a couple of flasher kits from an electronics store, but the flash rate is far too slow. The instructions state how to change the rate of flash but the flash rate is still too slow. One or the circuits uses a 555 timer to flash 2 leds and the other circuit is a metronome using a 4093B and a 4017B IC's and has flash as well as a tick sound from a small speaker. Ths flash and tick sound is ideal except for the flash speed. Any help/links much appreciated,
    Thanks,

    Regards,
    Jim
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Jim,
    Why don't you post your schematics of how the circuit(s) is/are wired currently, tell us what the flash rate is at this point, and what kind of flash rate you'd like to achieve?

    Without these few basic pieces of information, we'll go around in circles for quite a while.

    You can attach images using the "Go Advanced" button near the bottom, and then the "Manage Attachments" dialog.

    I prefer people to use .PNG format files as attachments, as they are generally small in size, quick to load, and are not "lossy" like .jpg format files.
     
  3. jim stapenell

    Thread Starter New Member

    May 21, 2009
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    I am not sure of what rate I want - must be fast enough to look like machine gun fire. Maybe 8 - 10 per second.
    I changed capacitor in the double flash circuit from 4.7u to 2.2u which sped up the flash rate of 1 led flash to 2.3 per second. Still far too slow. The flash and tick from the other circuit is about 2 led flashes per second = 4 ticks per second (tick = led on next tick = led off)
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    The 100KΩ is the easy one to change. I've have an article for something very, very similar here.

    555 Hysteretic Oscillator

    Do you want the ticks to match the flashes from the LEDs?
     
  5. Slider2732

    Member

    May 6, 2009
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    Been working on something similar for R/C myself. I see 9V mentioned for the 555 circuit, though they're very flexible with operating voltage. CMOS 555's can be triggered down to around 3V and if working with red LED's the voltage will be strong enough to drive them. But i'm guessing your'e probably on 3S li-po's @ 11.1V ?
    My circuit is a little different, in that I used transistors for a 1.5V flash...have been after the standard night flashes from real aircraft, from small power, so all is a lot slower in flash rate too.
    In most flasher circuits, the flash rate is determined by the values of the capacitor and the resistor. How long it takes to charge the capacitor to a threshold amount, dictated by the resistor.
    My usual tweak is to put a small variable pot in place of a resistor and turn it til my flash rate is what I want. The duty cycle won't be too important with machine guns, though I should think you'll want to tweak around with that to get the best looking effect in daylight as well as night. The perceived brightness and flash length changes like night and day, in night and day. The use of a pot fitted in your electronics pod might well be an idea.
     
  6. jim stapenell

    Thread Starter New Member

    May 21, 2009
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    Hi Bill, I don't think the ticks need to be in sync with the LEDs as there are going to be 6 LEDs "firing" at the same time. I dont think anyone will be able to pick any out of sync if firing rapidly.

    Thanks for the link, I will give it a try
    Regards,
    Jim
     
  7. jim stapenell

    Thread Starter New Member

    May 21, 2009
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    G'day "Slider2732" Thanks for your help..... I am building an Airwolf heli with Trex 600 electric mechanics - running 2x3s lipos = 1x6s and a separate 3s to supply the radio and leds.
    I now have several options for my "machine guns" to experiment with.
    Regards,

    Jim
     
  8. Slider2732

    Member

    May 6, 2009
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    Ah yes, name is Mark :)
    The 555 circuit I think is the easiest to work with, purely to get something working right inside the copter. I'm just thinking that the audio from the clicks on the metronome may be heavily damped by the rotor sounds and distance from the observer...may well be very wrong though.
    The sizing of the 555 circuit need only be the 8 legged chip and the resistor/capacitor, with less soldering to break. Personally, i've been guilty of soldering the components right on to the legs of a 555 in space crucial circuits. Points perhaps important for R/C, but maybe not at 1.5m scale :)
    I built a metronome for my wife recently, but the less said about it's volume the better, being as I posted about it having that issue on here lol
    Anyway, all is an aside if you want the decent volume tones, I realise that.
     
  9. jim stapenell

    Thread Starter New Member

    May 21, 2009
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    Hi Mark,
    You are probably right about the tick sound being overpowered by the heli mechanics. Even the electric helis are quite loud - but not as loud as a nitro. I thought it might be worth a try. I will experiment with the suggestions that I have received so far and try to get the LEDs flashing faster.

    Thanks,

    Jim
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Been having some trouble getting back on at this end.

    I've never built it, and I will hear about the lack of a resistor between pin 3 and the capacitor, but as long as it is a low freq buzz I don't think it is needed. Give it a try and see what you think. I was going for maximum volume.

    If you hear a pure audio tone the frequency is adjusted too high, and the 555 is at risk. Go for the maximum resistance to start with.

    The diode can be eliminated, I put it in because I think it will help the sound.

    [​IMG]
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Jim,
    In the 555 circuit, since you've replaced the 4.7uF cap with a 2.2uF cap, try reducing the 100k resistor to in the range of 62k down to around 39k.; I'm thinking 56k will be about what you want. Much lower than 39k, and it'll flash too fast to see.

    I don't know offhand what guns are mounted on your helo. An M16A1 has a cyclic rate of fire of 750 rounds per minute (12.5/second); a .50 cal M2 Browning has a cyclic rate of fire of 450-575 rounds per minute (7.5-9.58/second), M60 is 550 rounds per minute (9.16/sec). However, if you try to flash the LEDs much more than 11 cps or so, you won't see the flashing due to persistence of vision.
     
  12. Søren

    Senior Member

    Sep 2, 2006
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    28
    Hi,

    Several parameters should be scaled differently when scaling down a model to look authentic (just like you change a single letter of a font when you scale it to keep it looking the same).

    The rate of Mg fire would best be set by eye, butone thing that seems to not have been covered here is the M/S-rate. If you make the flashes short (with a higher current), the flashes will look much more authentic.

    The best pattern to simulate Mg fire is a fast bright pulse with a slow(ish) decay, something like this:
    __|\_______|\_______|\_______|\__
    (Hope that this ASCII drawing makes sense).
     
  13. Wendy

    Moderator

    Mar 24, 2008
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    I thought of something similar, set a 555 or something similar for a 50ms pulse, then vary the off time. This is a another common 555 configuration, using one more resistor.
     
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