Home made electronic igniter

[Olias]

I would like to know how to go about building my own electronic igniter (for lack of a better term) to light my smoke cartridges on my plane instead of having to physically light a fuse before take off.

My basic understanding says that I could use a servo extension lead. They have a Neg., Pos., and Signal wire. I'm thinking for the "Electronic Fuse" portion that I could use one of those igniters/fuses that the hobby rockets use. My question is, do I simply use the Pos. & Neg. wires hooked up to the fuse? If so, do I have to do anything with the signal wire? Or do the signal wire and Pos. lead need to be in contact with each other?

The servo lead would be plugged into one of my Aux. channels on the RX and then I could theoretically just flip a switch on my TX after the plane is in the air.

Any suggestions or help would be greatly appreciated. Thanks

Bryan

[pldaniels]

You need a switch device to control the power to the 'fuse' (like a rocket igniter fuse), the switch device has to listen to the 'width' of the servo pulse and trigger when it is above or below a preset value. That way you can fire your ignitor using your gear or AUX switch.

There's a million and one designs out there, including a few commercial ones (of which I produce some).

Where you have to be careful though is to ensure you limit the amount of current that flows into the fuse/ignitor if you're using the receiver/servo rails. You may well need an external battery source to prevent interrupting the flight system.

My own switches are at - http://www.nqrc.com/?vp=PLD-RCS-1A or http://www.nqrc.com/?vp=PLD-RCS-RL2A

Good luck :)

[Olias]

Well I'm sure glad I asked! I thought about interfering with the RX's signal and whether I'd need a separate power supply etc. That would be no fun losing my plane just in experimenting. Ok, I'll take a look at your links. Thanks very much for the input.

Bryan

Edit: Hmm....just noticed you are located down under. :( Shipping probably costs more than the item itself??

[darkith]

A cheap way to do it would be to use an old brushed ESC. Flipping the switch would give you full power on the ESC and light the igniter.

As pldaniels says, you might want to use a separate supply battery to avoid brownouts of the RX. And disconnect the ESC signal lead's red wire so you don't try to feed the RX power from the ESC's BEC.

D.

[vintage1]

A cheap way to do it would be to use an old brushed ESC. Flipping the switch would give you full power on the ESC and light the igniter.

As pldaniels says, you might want to use a separate supply battery to avoid brownouts of the RX. And disconnect the ESC signal lead's red wire so you don't try to feed the RX power from the ESC's BEC.

D.

We used to use fuse wire shorted across a battery wound round match heads in my crazy teenage days. And of course weedkiller and coaldust or sugar. Genearally to blow up, preferably in the air, the plane we had repaired once too often..

Another good trick was the above mentioned ignition system inside an empty humbrol pain tin, refilled with the usual IED mixture.

Prices went to who could blow the tin the highest.

A piece of thin wire can easily be driven to orange heat by a simple brushed ESC. Points to watch out are if the ESC blows before the wire does. Try a single strand stripped from a multi strand cable. And probably 25A ESC, but mostly the wire should blow first.

[Olias]

Thanks again guys. I was wondering if a brushed ESC might work or not. I just happen to have a couple 25 amp brushed ESC's laying around doing nothing now that I've gone brushless on everything. I think I'd definitely use a separate battery for it. I'm just not sure/clear on if it'll interfere with the primary ESC's signal or what ever or fry the RX when I flip the switch.

Bryan

[dmccormick001]

If you want to build your own device to do this, and you can program a PIC, here's a cool little circuit that weighs almost nothing. Use it just like a mechanical switch, and allow it to control current from a seperate battery in the plane that's just for the ignitor(s). If you don't need the extremely small size and weight, order the chip in the larger DIP size.

http://www.rc-cam.com/bitsw.htm

If you don't want to program a PIC, you could just install another servo in the plane, plug it into the gear channel, and allow the arm on the servo to close the contacts on a small micro switch like those available at Radio Shack. Or just let it push a couple of brass strips together to make the connection. It will take a little imagination and ingenuity to put it together, but that's what this forum is all about. Again, use a seperate battery of the correct size/voltage for the ignitor(s). You might want to test it up high to make sure you don't get any RFI (interference) from the switch/contacts that might cause you problems with the plane's controls.

[darkith]

We used to use fuse wire shorted across a battery wound round match heads in my crazy teenage days. And of course weedkiller and coaldust or sugar. Genearally to blow up, preferably in the air, the plane we had repaired once too often..

Another good trick was the above mentioned ignition system inside an empty humbrol pain tin, refilled with the usual IED mixture.

Prices went to who could blow the tin the highest.

A piece of thin wire can easily be driven to orange heat by a simple brushed ESC. Points to watch out are if the ESC blows before the wire does. Try a single strand stripped from a multi strand cable. And probably 25A ESC, but mostly the wire should blow first.

Yeah, for me it was either steel wool, or later on, nichrome. Used to be able to get Saltpeter and sulfur at any local drug store without ending up on a government list...

Thanks again guys. I was wondering if a brushed ESC might work or not. I just happen to have a couple 25 amp brushed ESC's laying around doing nothing now that I've gone brushless on everything. I think I'd definitely use a separate battery for it. I'm just not sure/clear on if it'll interfere with the primary ESC's signal or what ever or fry the RX when I flip the switch.

It shouldn't interfere. Basically, you'd have a separate battery and ESC setup....with *just* a shared ground a servo signal wire. As long as you don't send so much current that you turn the ESC into a pool of molten conducting slag, you should be fine.
For a test, you could always throw a fuse into the leads to limit any damage.

I seem to recall that my handheld rocket igniter worked on 4 AA batts, which I doubt are capable of too many amps. If you had a decent meter, you could measure the resistance of a few igniters to figure out the current through ohms law.

D.

[Olias]

It shouldn't interfere. Basically, you'd have a separate battery and ESC setup....with *just* a shared ground a servo signal wire. As long as you don't send so much current that you turn the ESC into a pool of molten conducting slag, you should be fine. For a test, you could always throw a fuse into the leads to limit any damage. I seem to recall that my handheld rocket igniter worked on 4 AA batts, which I doubt are capable of too many amps. If you had a decent meter, you could measure the resistance of a few igniters to figure out the current through ohms law.

Ok, people keep mentioning to make sure I don't send to much current to fry the ESC or switch mechanism. I'm a liitle worried about this as I have no idea how to find out how much current I need to fire off one of those fuses. I was just thinking of using a couple AA batteries or a 9volt battery...something in that range. And for sure I'd do several ground tests before I send my plane up with any set up. Isn't worth loosing my plane nor possibly sending a ball of flaming airplane into my friendly farmers field. :D I'm afraid my flying days there would be over in a hurry if that happens. :rolleyes:

And yes...I remember the good ol' days when I'd ride into town with my mom and whilst she was shopping I'd drop into the local pharmacy, hardware store, and or hobby shop and pick up all the saltpeter, sulfur, fuse, etc., that a 12 year old could carry. Made some great home made rockets and bombs. Also used to make my own fireworks. Anyway...getting way off topic here. Sorry.

Bryan

[BushmanLA]

I programmed a PIC to activate relays that would connect a rocket motor fuse to the battery. The PIC would watch for the appropriate stick position on whatever channel it was plugged into.

The relays were a dumb idea because they tend to weld themselves together from the inrush current when firing.

A better idea would be a nice big mosfet or transistor.

This might work for you as an all in one solution if it can handle the current needed to set off a rocket igniter.
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8833

You can get the rocket igniters with packs of rocket motors at WalMart or most toy/hobby stores.

Here are my results.
http://www.youtube.com/watch?v=gBn1h0x-37E

http://www.youtube.com/watch?v=jWEbbUczrYQ

http://www.youtube.com/watch?v=Hfoq065GXRA

http://www.youtube.com/watch?v=KiCg2XdYnB8

http://www.youtube.com/watch?v=jJKeWovxruU

[darkith]

I'm a liitle worried about this as I have no idea how to find out how much current I need to fire off one of those fuses.


Ohms law will tell you how much a igniter will draw. Use a meter to measure the resistance, and use the formula I=V/R (amps = voltage divided by resistance).
Unfortunately, the resistance may be very low and hard to measure.

So, resort to Google! I found this http://www.gwiz-partners.com/igniters.pdf
Which suggests that for various brand name igniters on 12V, the worse case scenario is around 23 amps for a brief moment, but most were much lower than that. An Estes igniter was 12.4 amps for 30ms. Note that this is how much current they were drawing...if you used a wimpier battery capable of less sustained current, the voltage would sag and they would draw less current. They'd still ignite, but it may take fractionally longer to heat up (probably measured in 10s-100s of milliseconds).

The 2nd portion of the above document shows the important of a separate battery. They tested a 9v battery as used on onboard rocket systems, and found that an igniter can briefly draw the voltage down to as low as 2.5v!!!

Now that I think about it, a fuse may still be a good idea, as I've had igniter wires get soft enough that they ended up touching after a rocket ignition, so it could short after ignition and blow the ESC.

D.

[jeffs555]

Found this thread on a rocketry forum. One guy there says he uses a single 70mah high C lipo to fire the Estes igniters. Would be very light if you had a brushed esc that would work with a single lipo.(would be light even with 2S 70mah lipos) The guy seems knowlegable and sells an altimeter that uses the same lipo to fire the parachute charges on model rockets. His post is around the middle of the thread. http://www.rocketryforum.com/showthread.php?t=2330

[dmccormick001]

If I'm not mistaken, all the standard rocket launchers use 4 AA batteries. They're capable of delivering the necessary current even over the fairly long wire that separates the launcher from the firing button where the batteries are located. A decent 4-cell pack, even a small one like a 600mAh, will probably do the trick.

[coriolan]

A cheap way to do it would be to use an old brushed ESC. Flipping the switch would give you full power on the ESC and light the igniter.

As pldaniels says, you might want to use a separate supply battery to avoid brownouts of the RX. And disconnect the ESC signal lead's red wire so you don't try to feed the RX power from the ESC's BEC.

D.
A good way to control that esc as on/off only would be to plug it in channel#5(retract) which give a high and low pulse only controlled by a switch. Retract servos only have two positions, up or down

[Olias]

A good way to control that esc as on/off only would be to plug it in channel#5(retract) which give a high and low pulse only controlled by a switch. Retract servos only have two positions, up or down


Hmmm....good point. I had thought about that very thing myself but with my lack of knowledge of electrical currents etc., I thought that maybe the "on/off" only position for that particular switch/channel may be to intense of a surge since it wouldn't be a gradual input, if that makes any sense at all. I know what I'm trying to say but don't know how to say it. :o LOL

[coriolan]

Hmmm....good point. I had thought about that very thing myself but with my lack of knowledge of electrical currents etc., I thought that maybe the "on/off" only position for that particular switch/channel my be to intense of a surge since it wouldn't be a gradual input, if that makes any sense at all. I know what I'm trying to say but don't know how to say it. :o LOL
Retract channel switch produces either 1ms or 2ms pulse train so it will switch instantly from off to full on, I think most esc can handle that!