Wireless Relay Launch system from commercial components

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Well-Known Member
TRF Supporter
Jan 17, 2009
Reaction score
A few years ago, I had a Wireless launch system made by Radio-match. But they went away not long after I bought it. Old site archived here:

It was nice, though only had a range of 100 feet or so. And for whatever reasons, it stopped working 2-3 years ago.

I have finally made my own replacement using a wireless receiver and transmitter from here:


Tx is $31

Rx is $60

The Tx and Rx can run 4 relays. You use one button to turn a relay ON, another button to turn the relay OFF. I modified it for momentary use for relay 2 and 3, left relay 1 and 4 as on-off. I had wanted to be able to use the on-off to run a bubble machine. But for some reason once the electric motor comes on, the wireless relay receiver locks out so not only can it not be turned off, but the other relays are locked out too, so it would not launch anything. I added a separate dedicated relay to the bubble machine, but no good, it still locks up (and the bubble machine was using its own internal battery, so it was not an issue of shared power source. Well, OK, the relay I added WAS using the same 12V as the wireless receiver). So, I won’t be able to use it for bubbles, at least not unless I find someone who can figure out why it is doing that and some possible cure. For those who wonder what’s the deal with bubbles, they are useful for picking thermals for contest flying, and it would be nice to be able to remotely turn the machine on and off to save on bubble liquid, batteries, and replenishing both.

I did not want to risk frying the receiver’s relays (only rated for 5 amps), so I added an external “black box” that holds a 30 amp auto relay. Plus, a buzzer to sound anytime the unit is “firing”, and a continuity beeper, toggle switch to go from cont-check to armed for launch, and battery inside for the continuity beeper. Well, I have been doing that sort of thing, the “firing” buzzer, and continuity beeper and toggle switch since my first footswitch based relay system around 1993 or so (I think any relay system without an audible warning when it is firing is unsafe).

Have not launched with it yet, but did some field testing the other day. The range seems to be a around 300 feet. My old wireless system was unreliable past 100 feet (sometimes did not even do 100 feet). 300 feet is plenty for what I need, which is mostly for launching my own R/C Rocket Gliders while standing back 100-200 feet

OK, time for pics, attached below. I mounted the receiver and the Auto relay/continuity box to a 5.75 x 9” clipboard (the “clip” part removed). The receiver part (larger box on left side) is mostly self-evident, note the folding antenna. The firing relay/continuity box, on top is a buzzer that sounds when the relay fires, at bottom is a Piezo beeper for continuity, and in the middle is a toggle switch to go from continuity checking (bottom) to ready-for-launch arming (top). The red/black wiring at the bottom goes to the 12V battery, and the clear-ish wires at the top are the ignition leads. If the bugs do get worked out for the bubble machine, the wires simply plug into the receiver box like the blue and white wires do (those are the internal relay #3 outputs that go to the automotive relay in the little black box).

I made up a little custom holder for the wireless transmitter. Partly for attaching a neckstrap. But also to make the holder just the right size to fit into a recessed area on the face of my R/C Transmitter, so I can press the button with my left finger then grab the left (rudder) stick at ignition (right hand already on the right stick which is controlling elevator).

And final pic, a drawing for the wiring, which mostly involves the small homemade “black box” for the 30 amp relay, buzzer, and continuity.

- George Gassaway





Last edited:
FWIW - included below are pics of the Radio Match system I had before. You can see how the wireless transmitter was used with the R/C transmitter. The unit in the white case is the RadioMatch receiver with internal relays. Also, a photo of my homemade “black box” made for testing continuity with that system. The RadioMatch system had strong enough relays, so the black box was only for the purposes of warning when the system fired (Buzzer) and to switch from continuity beeper to armed for flight (plus internal 9V battery for continuity check).

BTW -that “firing” buzzer not only is a good safeguard, but also confirms that the system is firing properly. So if you count down, press the button, and DO hear the buzzer go off, but the rocket does not go, you know the system worked so it was a misfire or lost continuity. Sure beats not knowing if it was a real misfire, or if the wireless system was fouled up.

- George Gassaway


Last edited:
Seems like a real nice system. As for the receiver locking up when you turn the bubble machine on, my first guess would be RFI/EMI (Radio Frequency Interference/Electro Magnetic Interference) I assume the motor in the bubble machine is DC and has brushes. The arching of electricity between the commutator and brushes can cause radio frequency interference. This can also feed back along power wires as EMI and affect other circuits (your receiver box) This is why you shouldn't run your vacuum cleaner on the same circuit your computer is plugged into.

I see several solutions. If the problem is RFI, move the bubble machine further away from the receiver. 50 feet would probably be a good idea. A way you can check if this is the cause is to wrap the machine in aluminum foil, connect the foil to a wire and the wire to a metal tent stack pounded in the ground. Your making a Faraday cage for it. If that works, then the problem is definately RFI and you can put a neater cage inside the machine to shield the motor.

If the problem is EMI, a filter like you can buy at auto part stores for getting rid of the hiss in your radio caused by spark plugs. Much more common on older cars with older style AM radios, but you should still be able to pick up the EMI filters. Put this on the output wires from the receiver to prevent EMI feedback to the receiver. You said you added a power relay to the bubble machine that was controlled by the receiver. You might need to put the relay midway between the two. The RFI from the motor can be induced into the wires in some cases and since the control wire from the receiver run all the way to the bubble machine, the relay might not be doing any good.
Last edited:
Bypass capacitors or series inductors right at the bubble machine motor might be a good idea, as well.
I added a capacitor on the motor where the wires connect, but it made no difference (IIRC is was a 0.1 uF disc cap).

It seems it is RFI. I found out last night that it affects the receiver even when there is no wire connected to it whatsoever. If I have the bubble machine running and move it to within 2 feet, the wireless receiver becomes intermittent to totally nuts when I “fire” the launch relay portion.

I have not yet tried the foil trick. Due to the nature of the bubble machine, it may not be possible to totally enclose the motor, there will be at least one opening. The motor itself cannot be removed from within the plastic to wrap it, the plastic is glued or welded.

Thanks for the ideas.

BTW - I did get to use the wireless system today to launch 14 rockets. But it was not planned that way. This was a launch at a school, the kids built their own Alpha-3’s and flew them today. Before leaving home, I had removed from an equipment box some unnecessary electrical cords used only when we do HPR. Well, the plug-in power cord (from battery) going into the launch panel accidentally was among them. I was fearing I’d have to make the 45 minute round trip home to get the cord. But I had brought the wireless system for a planned “range test” using the football field to confirm if it really is 300 or more feet. Well, never got to do the range test, but used the wireless system to fly the 14 birds. Worked great, no problems. Of course those flights did not test the range of the system, since the kids were about 50 feet away (each flier got to press the button).

A couple of pics attached. One showing a launch, the boy in the green shirt pressing the button of the wireless remote. And BRB member Steward Jones is at the left. The other pic, the wireless system under the rack. Had already added the 5 micro clip leads to the pads before realizing the panel was missing the power cable.

- George Gassaway


Last edited:

Very nice set up! Seeing your system got me wondering... can you think of any safety related reasons why this couldn't or shouldn't be done with a 2.4 ghz spread spectrum system? I was thinking about using a Dimension Engineering BattleSwitch radio controlled 10A relay to replace the Linx 4-Relay Receiver in your schematic (I only need one relay). The other components would be a Spektrum DX-7 transmitter and an AR6100 receiver. My "black box" is a Pratt Hobbies launch controller. The idea would be to launch a rocket glider with an unused channel on the transmitter (like gear or aux2).



Last edited:
I was thinking about using a Dimension Engineering BattleSwitch radio controlled 10A relay to replace the Linx 4-Relay Receiver in your schematic (I only need one relay). The other components would be a Spektrum DX-7 transmitter and an AR6100 receiver.
I have not used Spread Spectrum 2.4 R/C gear yet.

My concerns about using any type of regular R/C has been interference,, or loss of signal, that with servos would make the servos jitter and therefore trigger any relay based on using them. Well, of course it is not the “servo” that is the problem there, it is the receiver causing the servos or solid state devices plugged into the receiver to go nuts as a result of some sort of R/C problem.

But if Spread Spectrum R/C is as “solid” as the other wireless type systems, then I would think it would be fine. Just note I have had zero experience with that kind of R/C gear, so I do not know if it just holds to its last valid signal (as more R/C receivers are tending to do these days), or can jitter when it starts losing the signal.

I will say that since the codes on the Linx system are not as numerous as I’d like (256 addresses in the Rx), I had wanted to use two of its relays in series, requiring both to fire, in order to trigger the 30 amp launch relay. I had thought I could do a little wiring surgery inside the wireless transmitter, so that by pressing one button (the #3 button), I would cause it to trigger both relay 3 and relay 2. But it was not that simple, so I have left it with just the #3 internal relay to fire.

Since those Battleswitch relays are sorta cheap at $25, I will suggest getting two of them, and putting them in series. And setting up the programming in your transmitter so that when you trigger one channel, you also trigger another channel (for the second relay). This was a safeguard some people used when they were using old-style R/C gear as rocket launch systems, except they would use two channels with servos pressing on lever switches (and unfortunately too often using model Airplane frequencies for their ground-launch R/C system that should have been using Surface (cars/boats) frequencies, as the device being operated by R/C did not fly). Of course even with two servos set up that way, bad interference or loss of signal could still have allowed both servos to move the wrong way and fire by accident.

Even if you do not get a second relay, be creative with the programming of your radio so you can try to avoid accidental ignition by hitting the switch by accident. So that you have to flip two switches. One to arm it, like a regular toggle, and one to trigger it, like the spring-loaded “trainer” switch. I did that with the air-start ignition system of my Orbital SkyDart Project’s SkyBooster, to stage the SkyDart. Of course this assumes you have a computer transmitter that would let you assign two switches to be in certain positions to enable the system to “fire”, whether you used one relay or two.

For a totally different reason I won’t bother to explain here, I had added a beeping piezo beeper that sounded off any time that I flipped a specific toggle switch. So for the SkyBooster, I used that existing modified toggle switch for the “Arming” switch, as the beeper would alert me if that switch was “on” or “armed”. And there have been at least two times when I bumped the spring loaded trainer switch (“fire”) which could have caused an accident if not for the arming toggle switch being “off”.

- George Gassaway
Last edited:

Thanks for your well considered and thoughtful reply. Lots of good advice there. Rather than hijack your thread, I'll start a new thread when I have resolved some of the issues you have raised.