# How To Build A Wireless Launch Controller

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#### llobdelljr

##### Active Member
Does anyone have plans/suggestions for building/buying a one pad wireless launch controller with a minimum range of 1000 feet? I do fairly well at soldering and electronics, as long as it's not SMT
Thanks!

#### Voyager1

##### Well-Known Member
TRF Supporter
I currently have a prototype multichannel wireless controller working based around Arduino Uno modules at each end with a 433 MHz RF shield and LCD shield at the controller end, and an 8 channel relay module and RF shield at the pad end. This design allows for multiple pad banks allowing for up to over 30 pads (5 banks of 6 pads) in total. The final system will use multiple diversity 921 MHz RF shields with a very secure packet protocol.

For your application of a single channel you could use a 2 or 4 relay shield at the pad end. You would require at least 2 relays: one for arming and one for ignition. It might also be useful to have a third for continuity testing. Without going into too much detail, you would require a message packet scheme with redundancy and error checking. You don't want any misfires!

As for your 1000' minimum requirement, typically RF modules are available with up to 100 mW output power, possibly up to 1W. You would need check your local RF regulations regarding frequency and power in the bands around 433 MHz or 915 MHz. An RF output of 100 mW can give you 1000' plus range, but you would require elevated antennas at each end. Just using the typical monopole antenna connected directly to your controller and pad module would not be very reliable at ground level, even with line-of-site communication, due to ground reflections, etc. This is frequency dependent, too.

There are many wireless relay modules available, but they might be limited in range, switching flexibility and security. I suggest you read the many threads on wireless launch controllers that are on this forum. You may find similar threads suggested at the bottom of this web page. Here are some links to these threads:

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#### jpbell

##### Well-Known Member
If you are going to do this, do it right, bluetooth, so you can launch using your mobile...you could even have a count down on your phone :-D

#### dcullen

##### Well-Known Member
If you are going to do this, do it right, bluetooth, so you can launch using your mobile...you could even have a count down on your phone :-D
Not so much, as he is spec'ing 1000' range. I'll assume HP so BT is not going to provide enough range for any safe HP distance

#### wjmoser

##### Active Member
Not so much, as he is spec'ing 1000' range. I'll assume HP so BT is not going to provide enough range for any safe HP distance
I think the assumption is there is still a box at the LCO station and a second box at the pad (1000 ft away give or take). The Bluetooth connection would be to the box at the LCO.

I've thrown an idea around in my head to use very directional antennas with WiFi, then using a router to connect to a Raspberry Pi or Arduino with a relay at the pad side. You could use a browser to initiate the launch from your phone.

One question is can the "safety key" be a software password?

#### OverTheTop

##### Well-Known Member
TRF Supporter
We are just building some new ones for our club.

Some Learnings:
* If you are going for long range RF link, then keep the antennas off the ground. Camera tripods, or light stands (from a hardware store: throw the lights away) make excellent supports for the antenna.
* We built ours into a Pelican case to keep the dust out.
* Go for robust RF connectors that will take punishment. We use N-type on the box and antenna lead. BNC and SMA are cute and cuddly but break easily.
* Design the outputs so that shorting the leads does not blow up output devices (typically FETs).
* Make spare leads to keep in the range box.

#### Zeus-cat

##### Well-Known Member
Our club just built one. I don't know the specs, but I might be able to get some info from the guy who built it. If you have the money, the Wilson system is absolutely top notch.

#### dcullen

##### Well-Known Member
I think the assumption is there is still a box at the LCO station and a second box at the pad (1000 ft away give or take). The Bluetooth connection would be to the box at the LCO.

I've thrown an idea around in my head to use very directional antennas with WiFi, then using a router to connect to a Raspberry Pi or Arduino with a relay at the pad side. You could use a browser to initiate the launch from your phone.

One question is can the "safety key" be a software password?
you could use wifi but Xbees are easy to work with and available in both 2.4 gHz and 900 mHz high power versions. They are what WilsonFX uses for wireless link.

I think you need a physical key for the safety, but I'm not sure.

#### ksaves2

I made a system out of a wireless Chinese pyro ignition system. Cost me 60 bucks about 12 years ago. Does a coded transmission and it has excellent range. For a club systems one might want something more Bulletproof. Kurt

#### rockdoc

##### Well-Known Member
TRF Supporter
Wilson/FX has a great single pad wireless unit.

#### rharshberger

##### Well-Known Member
I think the assumption is there is still a box at the LCO station and a second box at the pad (1000 ft away give or take). The Bluetooth connection would be to the box at the LCO.

I've thrown an idea around in my head to use very directional antennas with WiFi, then using a router to connect to a Raspberry Pi or Arduino with a relay at the pad side. You could use a browser to initiate the launch from your phone.

One question is can the "safety key" be a software password?
I dont see why the "safety key" couldn't be software. So long as the unit absolutely can not fire without an unlock code and a button press the unit should be safe. Maybe even use a built in timeout so that if the launch button is not pressed within X number of seconds the unit automatically re-safes.

#### jsdemar

##### Well-Known Member
I dont see why the "safety key" couldn't be software. So long as the unit absolutely can not fire without an unlock code and a button press the unit should be safe. Maybe even use a built in timeout so that if the launch button is not pressed within X number of seconds the unit automatically re-safes.
Both NFPA 1122 @4.13.3 (Modroc) and NFPA 1127 @4.13.2 (HPR) require physical safety key disconnect switch in series with the launch button. The NAR/TRA safety codes are based on this. So, I think it would require clarification from the NAR/TRA to use a virtual safety key and virtual launch button.

#### ksaves2

I dont see why the "safety key" couldn't be software. So long as the unit absolutely can not fire without an unlock code and a button press the unit should be safe. Maybe even use a built in timeout so that if the launch button is not pressed within X number of seconds the unit automatically re-safes.
I bought an RfRemo tech transmitter that has a coded switchbox with four switches. I set the code on the transmitter, did a teaching procedure with my receivers
and if I scramble the four switches, one can push as many buttons as they want on the transmitter, it ain't gonna fire. Even with the power switch turned on. The switchbox is my "safety" switch. Unfortunately, that unit went out of production years ago. There are a variety of coded pyro firing devices the could conceivably be used but the receiver relays can only stand 10 amps. Best to use that to switch a higher capacity relay to shunt the marine or car battery current to the igniter.

If one has the coin, the Wilson F/X takes out all the guesswork for a club. For a lone flier, my setup is easily good for 1000' feet and probably more and it
makes it easy to do ground testing of research propellant. No long wire runs! Kurt

#### jdbwizzard

##### Well-Known Member
I have built our clubs wireless system and I'm in the final stages of working out the bugs. At the controller is a master key switch which connects the battery to the arduino, then there are selector switches to select a bank and the pads at that bank. As for transmitting it run of 2.4GHz devices. I have tested them up to 1200ft (the length of my street) in open air. The receivers are 4 channel relay banks. All of this is done with arduinos.

#### RocketRev

Howdy All,

Several have mentioned my product in this tread. So I thought I'd go ahead and say a few things.

1) Current TRA and NAR rules prohibit "virtual" removable safety keys. Both organizations currently require a physically removable key to disable every launch system used in this hobby. I suppose that either organization could change the current rules, but what about the NFPA? And worse, what prevents somebody else with a phone from using their bluetooth connections from their own device to bypass your phone altogether in order to control your key-less launch system? With all the ghost calling going on these days, I wouldn't trust any telephone based launch system. Its just too easy to break into.

2) Voyager 1, is absolutely correct that there are lots of "how to do it" threads, web-sites, etc., on how to do a single-pad wireless launch system. But I do not understand why Voyager 1 thinks you would need three different channels one for arming, another for a continuity check, and a third for ignition. I think his system needs some work. Prototypes are great. But they are still prototypes. Wilson F/X is way past a dozen generations of fully tested by rocketeer prototypes in hardware and software. Keep at it Voyager 1. It does seem like you might be on the right track eventually. But I have to say that using more than one channel to operate a single-pad system seems wasteful of hardware. W-F/X does the arming, continuity checking/reporting, voltage checking/reporting, ignition, and verification of each of these functions thru a single channel.

3) I have seen several Chinese wireless pyro systems, none of them are using legal USA frequencies or have enough range unless they are boosted beyond legal USA limits. All I can say is buyer beware.

4) There are dozens of groups using 900hp X-bee transmitters for various rocketry applications. At the recent Experimental Sounding Rocket Association launch, the organizers had to have clubs STOP testing their projects until they were ready to fly because the systems were interfering with each other in a bad way. Curiously, ERSA was using a fully wireless Wilson F/X encrypted launch system that also uses the same 900hp Xbee units but without any interference or degradation in system operation even before they asked folks to turn off their wireless rocketry packages until they were ready to fly. The W-F/X encrypted information transmission safety protocols effectively eliminate all interference.

5) A single-pad encrypted Wilson F/X wireless launch system costs $595 plus shipping. It will work out to at least a mile, even at Black Rock with the antennas 5 foot off the playa. And I guarantee my internal system technology for 10 years. Plus any future software upgrades except for shipping are free. Wilson F/X launch system technology has been operating in high power clubs for over 20 years being used/tested/proofed/checked/evaluated/reviewed by the toughest most critical users I can think of: Rocketeers. The original 64-pad Wilson F/X launch system is still operating after 15 years of hard use. And there are now over 33 clubs using WFX system on three continents. Well that's probably enough for now. If you're going to build your own single-pad wireless system.... Go for it. Make sure you check out the actual costs, but go for it. If you're going to look into buying a single-pad-wireless system? Email me at rocketrev@wilsonfx.com and we can talk. Brad, the "Rocket Rev.," Wilson #### Voyager1 ##### Well-Known Member TRF Supporter 2) Voyager 1, is absolutely correct that there are lots of "how to do it" threads, web-sites, etc., on how to do a single-pad wireless launch system. But I do not understand why Voyager 1 thinks you would need three different channels one for arming, another for a continuity check, and a third for ignition. I think his system needs some work. Prototypes are great. But they are still prototypes. Wilson F/X is way past a dozen generations of fully tested by rocketeer prototypes in hardware and software. Keep at it Voyager 1. It does seem like you might be on the right track eventually. But I have to say that using more than one channel to operate a single-pad system seems wasteful of hardware. W-F/X does the arming, continuity checking/reporting, voltage checking/reporting, ignition, and verification of each of these functions thru a single channel. Hi Brad, there may be a misunderstanding here. When I referred to channels, I was actually referring to 2 or 3 relay circuits on a single wireless channel. One relay for arming the ignition relay, and possibly a 3rd relay for continuity (although this is probably not necessary). Basically, I'm thinking of a double-switched (arm/fire) ignition system that will, hopefully, provide an extra safety margin, but only through a single wireless channel. If you like, the arm relay at the pad is like the removable safety key at the LC end. #### Sooner Boomer ##### Well-Known Member I think y'all are making this a lot harder than it has to be. You want to launch a rocket? You have to carry it to the pad. Why not do continuity checks AT the pad, rather than running back and forth to the "away" controller to see if you fixed it? Does NAR/NFPA/etc. say *where* the safety interlock has to be? Put it at the pad, too. Only when everyone is heading away from the pad preceding the launch, does the last person at the pad (the launch DIRECTOR perhaps?) enable the interlock and allow the firing circuit to be energized. This simplifies the problem a lot. Here's more help - stop (re- re- re-)inventing the wheel. There are already dozens of integrated circuits designed for remote control, both for transmit and receive. Yeah, they're intended for IR control of a TV. The principle is the same. Want increased security? Use a tone-encoder circuit before the transmitter, and tone decoder before receiver control chip (a 555 and 567 work a treat, and they're cheeeep). Even the transmit/receiver portions are readily available as turn-key parts, just hook them up and go. Many sources allow a selection of frequencies so you can find one that is in a "quite" band for your region. #### UhClem ##### Well-Known Member Does NAR/NFPA/etc. say *where* the safety interlock has to be? NFPA 1122 and 1127 both specify that you must have a removable safety interlock in series with the launch switch. #### BDB ##### Absent Minded Professor If you are going to do this, do it right, bluetooth, so you can launch using your mobile...you could even have a count down on your phone :-D There's an easy way to do this. Use the Eggtimer Quantum. You can control it from your phone via wifi. Just build a box for it, power it with a LiPo, place it near the launch pad, and attach the igniter to one of the deployment channels. It has a deployment charge testing function that you could use to light the igniter. Viola! Remote controlled launch system. #### ksaves2 ##### Lifetime Supporter TRF Lifetime Supporter There's an easy way to do this. Use the Eggtimer Quantum. You can control it from your phone via wifi. Just build a box for it, power it with a LiPo, place it near the launch pad, and attach the igniter to one of the deployment channels. It has a deployment charge testing function that you could use to light the igniter. Viola! Remote controlled launch system. Um, I suspect one would eventually toast the output transistors when an errant igniter doesn't open. The Rev is correct with the quotation of the rules above. Since many may fly alone or in small groups, you can take your chances but in a club situation if an adverse event were to occur, one could be left to hang out and dry on the basis of an "unapproved" launch system. Even if said launch system wasn't the reason for the adverse event. if a club is large enough with the financial means a system that is in compliance with all the regulations is prudent. Kurt #### BDB ##### Absent Minded Professor Good point. I'm planning to do the Quantum-hack-thing so I have a simple method for remotely igniting EX motors. I don't think it is advisable for a club launch. #### tsai ##### Well-Known Member I'm going to throw in my 2 cents on this topic... There's basically 2 categories here: 1) Chinese/cheap 343/433 MHz RF systems. You can buy or put one together for less than$200. These are single direction "remote fire" solutions.
2) Build something bi-directional using XBee or some similar radios, and write all the software.

I've done both. I started with some 433 MHz boards and put together a 4 pad system. Didn't cost a lot, and wasn't difficult at all. When I started using it, I ran into some major annoyances -
1) no continuity check at the controller station. Don't think you need it, but amazing how many times it's a useful extra check when you don't have it.
2) No voltage check of the pad box battery. If there is a continuity check, are you sure the battery has enough juice remaining?
3) Is the remote box "armed" or not, and can I disable the remote box from the controller. If the arm key on the controller is off, I'd like only the continuity circuits live at the pad. Reduce the chance of accidental launch.
4) etc... Turns out there are a lot of small useful things that are nice to have, especially as the pad gets further and further away.

Now, if you're OK with the above limitations/caveats, then you're good to go. Take a look at https://www.rfremotech.com/ - Looks like you can buy one of the new Alpha Fire modules for $13.20, and the 2000m transmitter for$19.00 and you're done. They also sell DIY components if you want to package them in your own casings.

Assuming you don't wan to compromise, so we move on to a bi-directional system. Now there's software to write, and a bunch of safety precautions and testing that absolutely HAVE to be in the software. This isn't like writing small scripts or web pages. This is more like writing medical equipment software. Worst case scenario with launch control software is that someone dies. Harsh, but true. No short-cuts with this software can be allowed.

The great part about this hobby is that there is so many different aspects from ground control electronics, to mechanical/materials engineering, and chemistry for motor making.

If you enjoy the challenge, I strongly encourage this path of exploration. I found it really fun and fulfilling. I even spent ~2 months (spread as a couple hours here and there over a few years) writing the software and playing with Arduinos, Xbees, and directly programmable Xbees. Lots of fun and lots of learning.

That said, I'm probably going to buy a personal Wilson F/X system to replace my homegrown units. I made everything work, but I'm tired of finding small bugs and edge cases in the code. I wrote the software to default "fail" for any unexpected reason, but that means that the system often won't launch when I think everything is correct. Now I have to troubleshoot which edge case I've hit, or what unexpected scenario has caused the system to disable itself. Fun at home while programming, but no fun when at the field trying to launch.

So, I guess to summarize. If you enjoy this challenge, by all means, please go for it. I did it, and it is fun. If you're doing this to save some money because "this isn't much different than a garage door opener," I would recommend you save yourself a LOT of time, and just buy the Wilson system. At the end of the day, the Wilson wireless system will actually cost less than the amount of time/money you would spend to build something even remotely equivalent.

Well, I guess a lot more that 2 cents at the end of the day. Cheers!

#### ksaves2

On the "no continuity thing" with the RfRemotech stuff, their receivers can only switch 10amps max. That means one
should use the receiver relay to energize a relay coil that switches a larger solenoid or relay. That battery/solenoid/relay box one can put in a continuity button. The thing there is one needs to put an appropriate resistor inline so
ematch based igniters don't "pop" when doing a continuity check. That is imperative. Me? When I'm doing a lone shark modroc launch by myself or a research motor burn, I don't bother with with continuity with my "big battery"
box. With a smaller parallel three 7.5amp/hour gel cell pack I have a buzzer inline for continuity and it works fine
with standard Nichrome igniters. I haven't tested it with ematches and am not going to use ematches for ignition purposes.
With a large club, toss some change into the collection plate for the good Reverend to supplement his meager income. The club has peace o' mind and a bulletproof system that
will likely last for years. Kurt

#### Voyager1

##### Well-Known Member
TRF Supporter
... Why not do continuity checks AT the pad, rather than running back and forth to the "away" controller to see if you fixed it? ...
With respect, that's not a good idea! I've witnessed a couple of high power motors igniting due to faulty continuity circuits. I would not like to be within a few feet of that! I'll run "back and forth" any day to have a safe launch.

#### RocketRev

Hello Voyager1. I would completely agree with you that there are far too many "unsafe" continuity checking circuits out there. But there are some continuity checking circuits out there that are proven to be safe. Wilson F/X has had an absolutely reliable and safe continuity testing circuit since our very first WFX digital launch system way back in 1994. Sure it was only a four pad system, but it did prove that digital programming/signaling could control multiple separate pads thru just two communications wires and you could test a flashbulb igniter with it with no chance of there being an accidental ignition. So9methings don't change and that's one of them.

So I would say that having a safe continuity circuit built into your system is very possible if you do it right.

#### Voyager1

##### Well-Known Member
TRF Supporter
So I would say that having a safe continuity circuit built into your system is very possible if you do it right.
Actually, in spite of my reservations about continuity testing at the pad, I do concede that IF it is done properly, it SHOULD be safe. In your case, I can understand that you've invested a great deal of development time and effort to get it right.

I guess I am applying the principle of "If it can go wrong, it will!". A little pessimistic perhaps, but given that some people making their own launch systems might be a little electronically-challenged, it is not a practice that I would recommend for them without supervision. As I mentioned before, I have witnessed unexpected ignitions due to faulty design and/or wiring techniques. Fortunately, these were controlled from the LC position, not at the pad.

#### OverTheTop

##### Well-Known Member
TRF Supporter
Actually, in spite of my reservations about continuity testing at the pad, I do concede that IF it is done properly, it SHOULD be safe.
That is my thoughts on the matter also. However I always get everyone to look away (and check that they do!) from the pads when I push the continuity button.

#### jsdemar

##### Well-Known Member
So I would say that having a safe continuity circuit built into your system is very possible if you do it right.
This was a thread on how to build a wireless launch controller. Now it's a commercial advertisement with vague inference on why yours is better. How about paying forward a little with specific suggestions on how to make a safe continuity circuit. Or start your own thread with [ADV] in the title. :wink:

#### cerving

##### Owner, Eggtimer Rocketry
TRF Supporter
A safe continuity circuit should use relatively low current, no more than a few mA, to light up a LED or drive a FET powering a buzzer. That's what virtually every at-the-pad continuity check circtut that I've seen uses. Since Quest Q2G2's are pretty much history, you don't see the same issue with a 6V incandescent light bulb firing the igniter, but there's no reason to design your system with one anymore.

I concur that it's better to use an XBee or some other similar module (Hope RF has some nice ones, cheap), but you have to design the software so that it's almost impossible to accidentally fire at the pad. That means some kind of coding that's different from one unit to another, so "your" controller can't light somebody else's pad. Oh, and it has to meet the FCC's guidelines too, even for a roll-your-own device... that means 433 MHz is out, unless you're a Ham and you have the control head send out your call sign every once in awhile. You could probably use any of the FCC-assigned R/C frequencies, the 75 MHz band for ground-control is probably your best choice since it's almost unused nowadays and you can have 750 mW of power. That should be more than enough to get you 1000' of ground range.

I'd be curious to see what Wilson uses for their keyswitch arming/disarming mechanism. It's obviously not a physical disconnect switch, since there's no physical connection between the control head and the pad relay box. My guess is that it's simply in series with the firing button... no keyswitch, no firing signal to the relay box.