Model Rocket Lauch Timer

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Mike
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Model Rocket Lauch Timer

Post by Mike »

I am looking for someone who can design an led countdown model rocket launcher for me. The thing is that I want it to count down for three seconds to launch. I have 3 leds, and once a second I want them to light. On the fourth second, about 6V needs to be sent through the igniter untl I turn off the circuit. To supply the power, I will use a 6V lantern battery, for the circuit and the launching. I need this cicuit to be designed with minumal parts, and with 555 timers only. Thanks to anybody who can help<p>-Mike
russlk
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Re: Model Rocket Lauch Timer

Post by russlk »

Is this a school project? Why only 555 timer?
Mike
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Re: Model Rocket Lauch Timer

Post by Mike »

Yes this is a school project, I am in 8th grade, but really like to build circuits. Our school has a rocket club, and I would like to build this for that. The 555 timers I have about 8 of, so I figured they would work good. I need minumul parts to keep it simple. One design I saw was on a web site and it is a decade counter hooked to a 555. The problem is that I am out of that counter, and it counts for ii seconds before closing a relay. I also don't want a relay, but instead a direct connection to the ignighter. I guess other parts would work, i just figured that the 555 would be easy and would work. I just don't know how to make it work.
-Mike
Mike
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Re: Model Rocket Lauch Timer

Post by Mike »

"...and it counts for ii seconds before closing a relay"<p>wow! I really messed up. the ii should be 11, and it should also state the fact that 11 seconds is too long, since I only need 3 for this project.<p>I was also wondering, is it possible to set up 4 555 (or 2 556, the dual 555) together so the output of the one after 1 second triggers a led and the next timer to start, that one does the same, and so does the third timer. The fourth would be the same, but it would hook to a rocket igniter directly instead of an led. That is just a thought that could be wrong. Please let me know if it would work and if so, what would the circuit diagram be?<p>Thanks again, Mike
Ron H
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Re: Model Rocket Lauch Timer

Post by Ron H »

Your thought processes are sound, Mike. The only problem I see is that you will never get the current you need for an igniter from a 555. A 555 will put out a few hundred milliamps best case. You need amps. See "Electrical Current Requirements of Model Rocket Igniters" for details. I suggest you trigger an SCR off the 4th 555. It should stay on ontil the igniter has burned itself out. Be sure you pick an SCR that can handle the current you expect.
BTW, I have never worked with model rockets, so this advice may be worth what you're paying for it. :) <p>Oh yeah, you want a schematic. That could take a little longer. :roll: <p>Ron<p>[ June 05, 2003: Message edited by: RonH ]</p>
larussell
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Re: Model Rocket Lauch Timer

Post by larussell »

I don't have time to draw a schematic but I can tell you how to hook it up. If you know enough to know to use cascaded 555s then I think you can figure out the details.<p>Look at Figure 1 in http://www.national.com/ds/LM/LM555.pdf<p>Connect a normally open pushbutton switch to ground to the input (pin 2) of the first stage. Connect the output (pin 3) of the first stage to the input of the next, for as many stages as you want. The LEDs go on the output of each stage, in series with a 470 ohm resistor where Normally On Load Resistor RL appears in Figure 1. You pick Resistor Ra and C so that Ra*C = 1 second, for instance 100K and 10uF. Make all the other connections as shown. When you push the button, the LEDs will light up one per second until they all are lit and the last output goes low. From here maybe someone else will tell you how to hook up the SCR. You reset the whole thing by removing power, which is what you MUST do while you're hooking up the igniter anyway. Don't ever mess with the rocket while this thing is powered, because if there's some glitch or noise or something else goes wrong, this thing could go off by itself.
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Edd
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Re: Model Rocket Lauch Timer

Post by Edd »

I guess you overlooked Tony’s site where he has an application. If you don’t need all of the bells and whistles they can be left off.It does utilize a preferred aural countdown sounding, after all who wants to be gazing down at a display or LED's, aren't all eyes on the rocket anyway ??? Also if you were set on the SCR it could be utilized in place of the darlington bipolar specified. If model rocket igniter technique is like I used , the current demands were rather low to glow a small folded wick of nichrome wire.Nothing in the order of the 15A or so required to.deploy a JATO unit ! Personally, one thing I would change would be the utilization of 5-way binding posts in place of the plug in to the igniter ckt along with adequate gauging of the connecting wiring and in times past..on my sons unit , the utilization of a block of fiberglass with a 2 connection Euro style of barrier strip that has set screws to make a positive clamp to the nichrome ends in place of the troublesome alligator clips that it replaced.
Your data URL is:
http://www.uoguelph.ca/~antoon/gadgets/rocket.html <p>
73's de Edd
[email protected] ............(Interstellar~~~~Warp~~~Speed)
[email protected]........(Firewalled-Spam*Cookies*Crumbs)

;)<p>[ June 06, 2003: Message edited by: Edd Whatley ]</p>
Mike
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Re: Model Rocket Lauch Timer

Post by Mike »

"The LEDs go on the output of each stage, in series with a 470 ohm resistor where Normally On Load Resistor RL appears in Figure 1" -Quote of nospam4russell.<p>Wouldn't the LEDs go on the normally off instead of normally on, since they are normally off until the timing is up? I could be wrong, but am just wondering.
desterline
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Re: Model Rocket Lauch Timer

Post by desterline »

Forgive me for being the wet blanket here, but has anybody considered the safety concerns?<p>Example: You push button, countdown starts, someone runs out on the field... How do you stop the launch?<p>Granted, three seconds is a short time, but this scenario is not unimaginable.<p>If you go through with such a design, at least put a safety switch in line with the igniter.<p>Good Luck
Denny
7474back2backcrashes
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Re: Model Rocket Lauch Timer

Post by 7474back2backcrashes »

I made some of the 11 second count types that you mentioned using a 555 as the clock driving a 4017 as the led count down driver. And yea, the overflow pin of the 4017 drives a relay because of the high current requirment of the igniter. You can choose any count ya want from the 4017. But it's also a good idea to have a continuity checker to see of the igniter has burned or not. They don't work everytime and sometimes ya get a dud shot or a dead short if the clips or bare igniter wires touch. Those little shorts will blow about anything except a relay driving the ignitor. Good luck cause trail and error forced me to use the relay. Always remember safety first and give the proper amount of time before approaching a rocket motor that didn't ignite after trying to launch it. Even after waiting you still hafta cross your fingers and hope your living right before checking it. Treat both ends of the rocket like a loaded gun and never get in the cross hairs if ya like your hands and face the way they are. :eek: good luck
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