How can I launch a rocket from 200 feet away?

[Max CR]

I am trying to launch a rocket 200 feet away from the rocket. When the switch is thrown to "ON" the electrical circuit is turned on which sends an electrical current into the motors. I can launch the rocket just fine if I am standing right there to flip the switch, but as i increase the distance of the switch from the rocket, then I need more batteries to the circuit. I have attempted to use this with about 4 nine volt batteries to no success. This is a parallel circuit. How can I launch this rocket from this distance??

I basically have to figure out a way to flip a switch to "on" from 200 feet away. Keep in mind that I do not want to pull on a string which will flip the switch! Thanks!

 

[Phrak]

Use smaller gauge wire. That is, wire, where the conductors are larger in diameter.

 

[turin]

Or use AC and transformers, the trick that the power companies use.

 

[sas3]

You could set up a simple timer with a wind-up alarm clock/Egg timer, or use a radio control device.
You could also use a small relay that turns on a connection to another battery next to the rocket.

 

[Max CR]

I am looking to spend the least amount of money possible so I don’t want to use transformers. I considered using a timer but I decided that after all of my work, I really want to be able to press that ignition button! What do you mean when you say I should use larger gauge wires? Are you saying that the copper inside of the wires should be thicker?

I considered using a radio controlled device but devices that used radio control going up to 200 feet got too expensive.

Now the relays seems like it could definitely be useful. The only problem is I don’t know anything about relays. I tried reading up on it by searching on google but I couldn’t find anything to explain to me exactly how the work. How could I use relays for this? Does anybody have any other ideas?

 

[Max CR]

Ok. How can I use the relay located at the following website for what I am trying to do? http://radioshack.com/product/index.jsp?productId=2062483&parentPage=family

Thanks

 

[negitron]

A relay is an electromechanical switch. You'd wire your button to the relay coil instead of to the igniters; it takes only a small current to energize the coil and pull in the contacts compared to the much larger current required to fire the igniters. You'd wire another battery through the relay contacts to the igniters. Since this battery would be right at the lauch pad, you won't have the voltage drop issues you have when trying to power a relatively large load through a long run of thin wires.

And, yes, as noted previously if you use thicker wires, you also reduce the voltage drop.

 

[turin]

Ah, yes, relay is a superb idea. Cheaper might be a power FET. How much current do you need to fire the rocket, do you know? If its on the order of amps, the power FET would be cheaper.

 

[Max CR]

Negitron,

Thank you. That was really useful advice. Now with the link I mentioned above, where will I attach the wires from the button that will turn on the relay, and where would I attach the circuit to ignite the rocket?

 

[Max CR]

The rocket needs 9.5 volts to launch

 

[negitron]

Refer to the data sheet for the linked relay:

http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/2750249_DS_EN.pdf

The wires running from your remote button and battery will connect to the terminals marked COIL; polarity doesn't matter.

At the launch pad, the battery (-) terminal will connect to one side of your parallel igniters and the (+) side will run to either of the COM terminals. Another wire will run from the NO terminal on the same side to the other side of the igniter array.

I would not use a FET, since a long wire run like that can easily pick up enough stray voltage to trigger it prematurely. In this case, low tech is safer.

 

[Max CR]

Wow Negitron! This has been a big problem that I have been trying to tackle for some time now. The idea to use a resistor definitely sounds like it will work. I never knew how to use a resistor until now. I knew that there was some way to use a switch to turn on a completely separate circuit and this is it! It definitely sounds like this will work. Thanks you! This definitely was something important that I needed to know.

I will try this out tomorrow. Feel free to watch the development of my rocket design at my blog, www.briancleaver.blogspot.com.

I do have one last question, though. Will this relay work if the two circuits are used with 9 volt batteries?

 

[negitron]

According to the data sheet, this relay has a minimum pulldown voltage of 9.6 volts. Combined with the voltage drop across 200 feet of wire, a single 9 V battery will probably not suffice. However, there are relays with other coil voltages available although I don't know what's available at Radio Shack. They probably have a 5-volt coil version, since that's a common TTL (a type of digital logic) voltage. That should pull in fine with a 9 V battery and all that wire.

 

[turin]

negitron, you don't think that a Gate resistor is sufficient? I was thinking of a simple voltage divider, with a large third resistance going to the gate.

 

[negitron]

I'm not sure I'd want to count on it when using motors big enough to burn my face off if they fire unexpectedly while I'm setting up. If the OP needs to be 200 feet back during launch, these are NOT little Estes A, B or even C motors.

 

[Max CR]

Haha. These are actually Estes D size motors. The only catch is there are about 36 of them with many of them igniting simultaneously.

Now, when you say that the drop down voltage is 9 volts, do you mean that in order to turn the relay on, you need to send 9 volts into the resistor? The website says “Pickup/dropout voltage 9.6/0.6VDC”. Doesn’t that mean that the minimum voltage to turn on the relay is 0.6 volts? I am also having trouble finding a relay that works with under 9 volts.

Thanks for all of the help.

 

[negitron]

Close. The pickup voltage is the minimum required to pull the relay in; the dropout voltage is the voltage below which the relay will let go. So, you need at least 9.6 volts to turn the relay on and then if the voltage goes below .6 volts, it will turn off again.

This one will work just fine:

http://www.radioshack.com/product/index.jsp?productId=2062480

 

[Max CR]

I looked at the description of that relay but I could not find any informatino about the pickup or dropout voltages. Where did you find that? It says 5 V does that mean that the relay will switch to on at 5 votls?

 

[negitron]

Yes, that's the nominal voltage; driving it with a 9 V battery will be fine, since it's not on continuously.

But, I just noticed it is limited to 1 A switching current, which is probably a lot less than what's needed to drive all those igniters. It'll work okay, but the contacts might burn out after only a few firings. This one might be better:

http://www.radioshack.com/product/index.jsp?productId=2049716

 

[Phrak]

In the expected enthusiasm, all sorts of higher technology solutions are put forward. For cheap, simple and reliable; get a small spool of bigger diameter wire.

How much bigger? Test it on a small engine to find out.

After more reliability? Put two batteries in series once you substanciate that one battery consistently works.

 

[negitron]

So, how much will it cost him to scrap the 400 feet of wire he has already AND buy 400 more feet of wire 2 or 3 wires sizes larger?

 

[Phrak]

So, how much will it cost him to scrap the 400 feet of wire he has already AND buy 400 more feet of wire 2 or 3 wires sizes larger?

Ha, ha Consider the electrical expertise of the questioner. I really like your idea, really. Not too involved. Reliable. If I were to do it, I would use your relay solution.

But are you going to supply a schematic to the OP?

I thought it was 200 feet. I'll find out how much 400 feet of ... 16 gauge wire will set him back, though. What do you think of 16 gauge stranded?

 

[negitron]

Well, it's 200 feet one way. Don't forget the return path.

Schematic, sure:

 

[Phrak]

http://www.mcmaster.com/#8104k112/=2ogvdz"

18 gauge white lamp cord (18 gauge). Total damages = $35, shipping included, one day delivery.

 

[Phrak]

Well, it's 200 feet one way. Don't forget the return path.

Schematic, sure:

You're fast. What are the contacts rated at?

 

[negitron]

Radio Shack: $4.49.

I win.

 

[Phrak]

Radio Shack: $4.49.

I win.

No you don't. What are the contacts rated at? A little short piece of nichrome is something like a dead short. How reliable is that after you've arced them a few times? Not reliable at all.

Next time you want to fire, you've got a dud.

 

[negitron]

12 a @ 120 vac.

 

[Phrak]

12 a @ 120 vac.

How many amps does a 1 inch length of nichrome #30 draw reduced by battery impedence and a couple feet of speaker wire?

OK, 4 inches of nichrome, as if it makes a difference.

 

[negitron]

Depends on what he's using. The instantaneous current can greatly exceed the stated continuous-duty rating of the relay without too much trouble, particularly since the current draw during the re-opening phase will be zero (because the igniters have fused open), ergo no arcing.