rocket ignition system

[ziomatrixacs]

hey guys.. I was tinkering wwith the idea of using one of those estas rocket engines as a cheap way of getting a glider to altitude..

the estas engines use a battery, I think its a 4.5v pack to ignite the engine. I took apart the launcher and its just a short circuit essentially. So you press a button, it shorts out the igniter fuse, and it causes a spark, causing the engine to ignite, and off you go!

My idea was to have a servo that controls a tow release and a switch to ignite the rocket. Of course the tow release goes first, then the ignition is second.

The RX battery would also be the ignition battery. It shouldnt use that much juice since its on just for a second, but i am not skilled at circuitry and i would like someone to look this plan over..

The ignition servo hits a switch that draws power from the main pack, causing it to short the fuse and ignites the motor. Im not sure if the split second short would cause my RX to loose power. I intend to have them hooked up in parelle configuration and not series so it should work technically but I was taught energy takes the path of least resistance, so the temportary short may cause it to loose power, and i wont be able to get the servo to disengauge the switch (but if it launches, the circuit will be broken since the fuse wires completly seperate after it ignites the engine.)

is it worth the risk of about $70 in parts ? does any one know of a better way instead of using a seperate pack? Im trying to keep the weight down..

[mjsas]

I would use a capacitor instead of the RX battery. Automotive air bags are set off with a capacitor so it does not take a real large cap. You could use a step up voltage converter to charge the cap to 12 or 24 volts to get more energy.

[ziomatrixacs]

sorry but I only understood part of that, could you explain more indepth ? I have next to no experience with electronics but I am willing to learn a little ..

[BushmanLA]

Ack!

Don't spend 70 bucks on this. You can do it for much less, at least I did.

I programmed a microcontoller to watch for two servo position signals from the receiver, one position is for arming the launcher, the other for firing it.

When the micro controller gets the right signals it simply activates a relay that connects the estes igniter to a battery.

In general the estes igniters require too much energy to be set off by what you can store in the common low voltage capacitor, but they also don't draw so much current that you will reset the receiver or fry your expensive lipo. The data on the estes box said something like .6 amps for half a second if I remember right.

An alternative is to get a high voltage capacitor and a high voltage source like a camera flash unit. This will probably have no problem setting off the igniter, you can get flash units from cheap disposable cameras, but if you don't know what you are doing, don't play with it. You can really shock the crap out of yourself (I know).


I launched the rockets from rails, and used the igniter itself to keep the rocket from falling off. Here are some vids, sorry I don't have any really good ones.

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

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

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

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


I originally made it to work on the xport of a Hobbyzone ship.
http://www.pasqualy.com/xport/


Then I realized it was too small and moved it over to my glow bird.
(before my brother wrecked it)
http://www.pasqualy.com/FPV/100_0679sml.jpg


Edit:
DOH! I just realized, you want to launch your plane using rockets, not use your plane to launch rockets :)

[ziomatrixacs]

Hey I have those little red rockets too!

I don't have a micro controller that is small enough. The one I have is about 3x5 inchs and I cant get the actual micro controller off. Its soldered to the board :(

Im not sure how you would charge the capacitor, and I just so happen to have one from an old polaroid laying around. Its actually heavier than my RX pack, so I dont think that is the best route. I am trying to keep the plane under 5 ounces, which is why I am trying to split the RX pack to the igniter.

I should clarify, I already own all of the parts to make this system, and in total, they cost about $70. (Two micro servos,One sub micro servo, micro RX, and a small 4.8v NiMh)

I also dont know if this will work or not, so I dont want to spend any more than 2-3 bucks on this thing.. I could convert it to EDF but thats alot of money since I dont have those componets laying around.

If I have to, I could just pop open a 9v battery, remove three of the 6 small (AAAA?) cells and then just use that..Still might be too heavy though. Would a 3.7v battery work? I have a 3.7v lipo that is only 130mah and is the size of my thumb nail, weights a gram, so I wouldnt mind using that.

[Comatose]

It'll work fine. The igniters don't pull more than an amp or so.

Rocket boost gliders are perfectly acceptable. A micro is a nice, clean way to go, but "servo hits a switch" is perfectly workable if those are the parts you have.

[ziomatrixacs]

Ah cool.. Im just following the KISS principle

[BushmanLA]

If you aren't setup for programming micro's and stuff then just go with having a servo touch two wires together.

a 3.7V lipo will probably be ok, you will want to test it of course. If that doesn't do it, try one of those itty bitty 12V batteries they sell at radio shack. It should be worth a few launches.

You might be disappointed with the rocket motors though, they tend to expend all their energy very quickly, like a swift kick in the butt instead of a nice long gentle push.

Some info
http://www.estesrockets.com/assets/downloads/launchsystemguide.pdf

You also probably want to get rockets with a low average thrust for the given total impulse. This means longer burn times. For example an estes C6 and a C8 will both provide the same amount of energy, however the C6 will provide it at a slower rate and for a longer time.

more info on that
http://www.estesrockets.com/enginefacts.php

[ziomatrixacs]

Yes, I have a thread about replacing Jetex and rapier motors with these Estas rockets..I know they have a higher discharge than a slow burn..but I can not find those engines instores. (I cant order on the internet)

Im willing to try it though, since these engines are cheap and available. I might use one of those bigo C or D's I had some laying around somehwere but I lost all of the fuses and plugs

[Acetronics]

Just for the pleasure of eyes ... :p


Alain

[BushmanLA]

Yes, I have a thread about replacing Jetex and rapier motors with these Estas rockets..I know they have a higher discharge than a slow burn..but I can not find those engines instores. (I cant order on the internet)

Im willing to try it though, since these engines are cheap and available. I might use one of those bigo C or D's I had some laying around somehwere but I lost all of the fuses and plugs

You can use small bits of steel wool instead. It helps if you coat them with a mix of gunpowder and nail polish. Experiment to find the right number of strands etc.

[jakflyer]

how would i go about wiring a relay to a reciever channel?

[BushmanLA]

how would i go about wiring a relay to a reciever channel?


A relay uses current through a coil to make a switch close. You need some kind of device that will watch for the appropriate stick position to operate the relay.
You could use a simple brushed speed controller, a micro controller, etc.

Depending on the application, you may not even need to have a relay. For example, a brushed speed controller is probably plenty enough to set off a rocket fuse by itself.

[ImaBiggles]

For example, a brushed speed controller is probably plenty enough to set off a rocket fuse by itself.


Yep, this was going to be my suggestion. Get a cheap 8 amp brushed ESC, hook it up to a channel you can control by switch. Make sure position 1 is 0 volts out of the ESC and position 2 is >5. Hook the esc up to an ignitor and when you flip the switch, off goes the rocket. Cheap brushed ESC is what, $8 now? Just pull the red wire out of the connector thats going to the RX to disable the BEC. Tee the same channel to a servo if you want to also control the tow cut with the it and have the igniter start a 4 sec fuse to ignite the rocket instead of directly (get the tow plane out of the way time).

[ziomatrixacs]

I got brushed escs out the yin yang! I got atleast 4 jeti 6 amp's and a GWS 2 amp, and a jeti 90 amp..

I thought about that but I was worried about it being a short, maybe there is some diode or micro fuse I could put in? Id hate to have to replace a fuse after every flight though..

[ImaBiggles]

I got brushed escs out the yin yang! I got atleast 4 jeti 6 amp's and a GWS 2 amp, and a jeti 90 amp..

I thought about that but I was worried about it being a short, maybe there is some diode or micro fuse I could put in? Id hate to have to replace a fuse after every flight though..
The igniter will act like a fuse. Never seen one that wasnt burnt through once setoff. use a 6amp and you should be fine as long as you remember to pull the red wire from the connector that goes to the RX (stops esc).

A diode will do you nothing, you can make the circuit as complicated as you want but that just means more crap to fail. KISS

[ziomatrixacs]

Alright, just remove the red wire to stop the BEC from working..got it. I can just have the power source be the main 4.8v NiMh pack?

Wait.. that doesnt make sense. I would use the 4.8v nimh to power the RX and then use it to power the ESC but the BEC would be disabled. Couldnt I plug the 4.8v Nimh into the ESC and run it like a normal electric plane but without an elevctric motor?

[jakflyer]

yeah i've used esc's before to start the rocket ignitors. i just took an old esc i had and used it the exact same way i would with a motor, except instead of a motor, i wired each side of the ignitor to the motor output leads. It worked fine.

[ziomatrixacs]

I am almost done building the plane..I got side tracked by a few foamies and my experiemental rocket plane exploding.

Ill be done in about 4 days probably. Im still deciding if I really want to put a rocket motor on this thing.. hmm