Ways to use an FM system.

[thathad2hurtbad]

I recently reciveved a VEX robotics kit for my birthday, and i noticed that the logic and controller of the robot are very advanced. And seeing as the controller is the same type used to fly model planes, I am going to guess that it has a rather long wave capability. So I was wondering if there was any way I could modify this thing to be a sort of variation on the old Cell Phone Detonator. It uses a 61 wavelength FM wave to transmit controls, which worries me because there are undoubtledy other FM radio waves in the air, and i would not like to have the ignitor go off prematurely.

The only thing I can think of is linking the FM reciever to the detonator and programming the controller so that when i move the joystick up it will create a spark causing it to ignite, but I may lose the FM reciever during this.

Any Suggestions?

[evilgecko]

Sounds pretty risky 2 me. I used to have this RC Car that used to start moving all by itself after picking up stray radio signals. Although if you are able to program the chip only to accept signals from your transmitter, than it might be worth a try. Similar to radio controlled garage door openers, they send a unique pulse to the reciever first so that only you can open the door.

 

Then I just thought, why not use a RC garage door opener? I reckon their range could be extended with a larger antenna and maybe a bit more amplificaiton power if you knew a little about electronics.

[Rogue Chemist]

Yeah RC toys arent so good for such, I once had a remote control car that if put infront of a TV that was on it would vibrate in place. I did make a remote ignition system with it but that was only for the kick of having a cap go off when I turned the TV on...

[thathad2hurtbad]

You guys just saved me from getting my fingers blown off, thanks.

But the garage door opener one intrigues me.I know that they have the antennea inside of the plastic, how would i extend it?

[Dr.Bodgy]

I can see heaps of potential problems with RC toys as dets.

The door opener is a good idea because of the unique code and posible frequency needed to open it.

The antenna would need some work, you would need to find out what wavelenth the unit is set to recieve on and build a high gain antenna to suit.

( I can design a really, really cheap one for you to build if you PM me the frequency ). You may want to put a larger antenna on the remote to.

Every 3dB of extra gain your antenna at the transmitter has it will efectivle double the radiated power and thus increase distance...

[evilgecko]

Dr.Bodgy knows more about this than me but yeah you can't just slap on any length of wire onto the antenna to make it better like you can with FM radio it will just make it worse. It needs to be properly designed so that it picks up the right frequency. Cellphones are also very dependant on antenna design.

 

If you took the drive unit of a door opener apart and removed the circuitry you should be able to locate the antenna. And it will also proberly have a useful relay already attached for turning on the electric motor which could be used to switch the ignition circuit.

 

Does power drop of the the ^1/2 of distance? Eg R is propertional to P^1/2?

[Dr.Bodgy]

Any antenna will pick up any frequency, but it is only resonant at one frequency, thus the need for tuning.

The antenna on most RF remotes is generally of isotropic design ( I think that is the word ) and is printed on the PCB... very inefficient.

30000 / X = Y Where X is frequency in MHZ and Y is wavelength in centimeters. The most simplest, biggest bang for the buck antenna is a quarter wave. It requies no BALUN, good impedance match and can be made from any thing.

[Boomer]

My two cents:

 

Even if it is less fun to have a delay between pressing the button and BOOM, add some fuse. This way, if the electronics fails, you still got time to get a little away. Or better, use some wire between receiver and charge. This also prevents destruction of the receiver...

 

And field strength drops with the SQUARE of distance, ten times the range needs 100 times the power (unfortunately)!

[Swany]

I belive I am going to construct something like this, using about 50ft of wire to keep the reciever somewhat away from my charge.

 

I have a few 2, 3, 4 etc. channel radios (and servos) from dead or dying RC projects. I plan on making a system such that when you turn 2 servos 100%, it will complete a circut and will fire a switch or something that activates a normal E-match. It will basically just be a remotely fired E-match that uses 2 buttons and 2 servos(rather than fingers) to complete the circut.

 

Here is my blueprint a la MS paint

[evilgecko]

Thats a good idea to use two radios instead of one. You're going to use recievers and transmitters of different frequencies so that a stray signal can't set of both, right?

 

A thousand pardons but what are servos?

[TheSidewinder]

The servo is the actuating mechanism for a radio-controlled device. These are little motors, geared down, that turn or move an arm attached to them, providing the motion that moves control surfaces.

 

http://www.futaba.com/products/hrc/overvie.../bnr_servos.jpg

 

That link is a picture of some servos by Futaba, one of the leaders in the hobby RC market.

 

M

[Swany]

I will stick with one radio for simplicity's sake. The odds of 2 servos cranking to 100% in the same direction due to interferance, in the middle of nowhere, are not likely. My radio gear is also pretty high quality, and has some protection to minimize the effects of such interferance.

[evilgecko]

What if you used one radio as an arm function? Instead of having it connected to a servo just make go straight from the reciever to a relay (some amplification may be needed to turn the relay on), so that when you send a signal the relay contacts shut on the ignition circuit. Then the servo is driven to 100% and kaboom.

 

I just don't like the idea of having a single trigger for safety reasons.

[TheSidewinder]

That really won't work. The way an RC system works is that the radio sends out a pulse-coded, FM modulated signal that the receiver "translates" (for want of a better term) into signals that the servos can understand. Merely hooking up a relay, however you try it, isn't going to do anything.

 

The outputs to the servos from an RC receiver always have voltage on them, and cause the servos to move by making digital "adjustments" to the pulse widths, which the servos understand to move in one direction or another. About the only way I'd *ever* consider doing something like that is two seperate systems, with a BIG difference in their operating frequencies, and *two* servos on *each* system having to "line up" however you require before ignition occurs. That would make it prohibitively expensive, as you'd be blowing up 4 servos and 2 receivers every time....

 

M

[evilgecko]

Ohhhhh so servos are not just a fancy name for a motor they sound complicated. I think Swany is planning on locating the recievers out of the blast zone and using some wire to connect the servo to ignitor.

[TheSidewinder]

Hmm.. well, at that point, why not use a pyro firing panel?

 

M

[Swany]

Well, this would also see use with high explosives, and SFX. This means that the unit, if too close to the charge, could be... killed in a number of scary ways.

 

Look at it like this: - - - is my signal traveling to reciever, == is the wire, () is charge, [] is reciever.

 

Me- - - - - - - - - - - - - - - - - - - - - - - - - - - - - []=======()

 

Ok, ugly, but you get the point. Basically it just allows me to go wherever I want to observe, a hill, whatever, and I can be safely away for stuff that is either too large for my current firing board, or I just want a different angle.

[PyroJoe]

Somebody posted a wireless ignition system, orignally for airsoft claymores sometime ago. Here is the site:

 

http://www.supercelldev.com/store

 

Scroll down that page for the "wireless do it yourselfer" you can buy just the bare bones circuitry or with the plastic project boxes.

 

Im not sure how suseptable it would be to recieving interference, but I bet it would be much better than an r/c car. It comes with a keychain remote that has 2 fire buttons, so you can set off 2 different devices. Instead, I was thinking of hooking up the 1st firing sequence to a relay that enables the 2nd firing sequence, so for added safety you hold the 1st button down while you press the 2nd button to fire the device. Seems like $40 is a decent price if it has good range and no interference.

 

I would also use swany's idea for the ignition, I have an old casing from a car power inverter that I would put everything in. It is made form 1/8" thick metal, probably aluminum, but it's very strong and would sustain quite a blast.

[snow]

I belive I am going to construct something like this, using about 50ft of wire to keep the reciever somewhat away from my charge.

 

I have a few 2, 3, 4 etc. channel radios (and servos) from dead or dying RC projects. I plan on making a system such that when you turn 2 servos 100%, it will complete a circut and will fire a switch or something that activates a normal E-match. It will basically just be a remotely fired E-match that uses 2 buttons and 2 servos(rather than fingers) to complete the circut.

 

Here is my blueprint a la MS paint

aamm that is the most stupid thing i have ever saw....

the reciver it self acts like a swich and a battary... you need only connect long wires and the fuse matirial

 

and about all this idea to use this reciver i think it is realy ****** ******

this only reciver+transmiter i gess costs like 100-150$ !!

so why to use it in explosive uses and you get a toy car for 10$ and modify the reciver+transmiter and every time it will explode (yes even long wires can sometimes no prevent the recivers explotion) so i think 15$ is a little less then 100-150$

 

im also from israel

[aquaman]

The only bad thing about RC cars is that cheap ones have tendency to glitch and those glitches sometimes ignite the E-match. so using rc cars is not the best thing. I myself have used rc cars and every now and then there'll be a couple of times that they ignite when I really don't want them to ignite and they scare the crap out of me. That is basically the only reason why I stopped using them, even though I did like being able to ignite things from inside my house .

 

At least with servos a noramal glitch won't turn the servo the whole 60°. I said normal because I do have those expensive $300 rc cars and they do sometimes have really bad glitches.

 

So if your going to ignite something that can seriously hurt I wouldn't use a RC car's RX/TX (Reciever/Transmiter).

[Swany]

The only reason I am considering using quality radio gear, is because, I have large amounts of it. People who own RC cars, good and bad, bring be all of their dead stuff, or when their car gets totaled, they dont bother to salvage anything, so they take it to me. I have boxes of radio gear to use, as a result.

 

It would be placed in a padded box, filled with foam and other material, and It would be a ways away. I could use a cheap car, but I also don't get the range that I could get with the more expensive radio gear.

[aquaman]

Try the gear if you see no glitches try it. But there's always a risk of it glitching on you and always keep that in mind.

[snow]

The only bad thing about RC cars is that cheap ones have tendency to glitch and those glitches sometimes ignite the E-match. so using rc cars is not the best thing. I myself have used rc cars and every now and then there'll be a couple of times that they ignite when I really don't want them to ignite and they scare the crap out of me. That is basically the only reason why I stopped using them, even though I did like being able to ignite things from inside my house .

 

At least with servos a noramal glitch won't turn the servo the whole 60°. I said normal because I do have those expensive $300 rc cars and they do sometimes have really bad glitches.

 

So if your going to ignite something that can seriously hurt I wouldn't use a RC car's RX/TX (Reciever/Transmiter).

yes thats why i wrote and change them alittle

i meant coding the signal and the most easy way to do it is by transmitting low friquensy like 20HZ and on the reciver add a fillter to 20 HZ these fillters circuits you can fine all over the net... and all this will cost:

the waiver (i dont know how you say it in eng lol) one time build ~3$

and the fillter 0.5$...

thats all

by the way aquaman=aqua the one from israel?

[snow]

by the way if you want things more safe and less expensive

the timers based 555 is the best thing

and their circuits you can fine all over the net

snow

[they call me 9 fingers]

Hey whats up every one. First things first,I am new hear so whats up. Secondly sorry for resurecting a old thread. Well i have built a raidio ignition system for my pyro, actually it is much simpler than you would think, basically you take a simpl relay or transistor circuit, where when the relay has power applied to it the circute is compleated igniting the pyro. Well i took a pair of raidios, the GMRS motarola type, they have a range of about 8 miles and you can set privacy codes on then. They just happen to have a external headphone jack on them so that got me thinking. i found a old jack and wired that into my relay circuit their is enough juice coming out of the speaker wire to actually throw the relay. The only problem i see with this sytem is some one else keying their radio on your channel, but with the privacy codes that cuts down on the posibility. I will try to get pictures posted soon