16 Rocket Semi-Simultaneous Launch Controller - Page 1
Forum section: electronics / projects

author: LydaRA
author_rank: Contributor
timestamp: April 25, 2021, 06:54:11 pm
content: So about to buy parts for a Cub Scout model rocket launch control system! Yay!!!It is made of multiple boxes, each with a big 12V battery and an Arduino, networked together. At the launch pads, each Pad Box needs to power both the static 5V control logic AND 12V through relays to between one and eight model rocket igniters. Although the RSO has the Master Arm, _each_ Scout has their own Launch Button.Any thoughts on what DC : DC power supply I might use? For the Pad Boxes, the big 12V motorcycle battery needs to supply:1) 5V to Arduino2) 5V to relay drivers3) 12V to quantity 1-8 x 1-2Amp each ignitersBut that means the Amps could swing a good bit:1) If firing all 8 rocket igniters at once, then large cumulative load. Got to make sure still enough not to starve the Arduino.2) If only firing one rocket (a lone scout goes early or late), too much current to one channel? Got to make sure not to weld relay or melt other components.Thanks in advance for any suggestions on batteries and regulators (or anything else)!Robert Lyda, Sr.ASM, Troop 148COPE & Climb Level IIWAC Rockets LeadNRA RSO

author: Domagoj T
author_rank: Frequent Contributor
timestamp: April 25, 2021, 08:06:55 pm
content: Don't worry about only one igniter drawing too much current. It will draw only as much as it needs and not more.The only concern is that the battery should be sized such that it is capable of providing enough current for all igniters to light up simultaneously (and have some room to spare).Arduinos usually have a voltage regulator, so they can take 12V and drop it to 5V for their needs and if there are not too many peripheral consumers on the 5V line.Depending on the relays, the regulator on the Arduino may be adequate for that as well, but keep in mind that Arduino output pins can not power the electromagnet coil on the relay directly. Are you using some ready made solution or making your own?

author: LydaRA
author_rank: Contributor
timestamp: April 25, 2021, 08:20:45 pm
content: To drive an eight relay board, too much output current across 8 GPIO pins. That's why I show a separate 5V supply connection for the driver. The Arduino only needs to send TTL logic to the driver board, not power the coils.Probably going to use a pre-made relay board. Looking for pre-made power supply as well. Just too small, simple, and cheap to get bogged down building the "commodity" parts. Frees me to focus on more use case parts, adding safety. Tradeoff is indeed that if one out of eight relays bites dust, pain to repair or waste to replace whole thing.

author: phil from seattle
author_rank: Super Contributor
timestamp: April 25, 2021, 08:32:11 pm
content: I think you are saying you will have up to 8 igniters per battery, controlled by 1 Arduino. So, your max current is 16+arduino+relay coils. Most automotive batteries have pretty good "cranking" current so you will likely be ok. Don't worry about a single igniter being overwhelmed - it will draw only the current it needs.You could use a much smaller battery by having the arduino serialize the igniter firings and reduce maximum current to just 2A+arduino+relay coil. I don't know how long it takes to ignite (and thus burn out the igniter) but let's say it takes 200 mS. So, if you see all 8 firing buttons pushed, close the first relay, wait 200 mS, open the first relay, close the second, wait 200 mS, and so on. If you wanted to be fair, you could get the time of each button closing and close the relays in the order of the buttons being pushed.By the way, I would use 12V relays. Avoid sharing the arduino power rail with the relay coils.For the arduino power section, I would use an off the shelf 12V to 5V DC Stepdown converter, 1 Amp would be fine. You could protect this with a large electrolytic capacitor(470 uF 25V) and a diode (1N4001 would be good) in series to prevent battery droop from causing a problem. Think of the diode as a "check valve". The diode would also prevent a reversed battery from damaging your arduino.

author: LydaRA
author_rank: Contributor
timestamp: April 25, 2021, 10:40:49 pm
content: Yes, thanks!I was thinking this could probably be done with a smaller motorcycle or even "PowerWheels" or Dewalt tool battery. Even if there is a poor contact between the igniter and the solid powder engine, after a couple of seconds at 2A....either the rocket has gone or it won't.Not a bad idea of sequencing the launches. Just have to see how long the Arduino-to-Arduino communication drags out. Given we're dealing with children's attention spans, got to keep it "snappy." For as long as the RSO allows (two or three seconds), I was going to just keep looping to copy whatever buttons are pushed forwarding to the igniters. Expected that as igniters burned off, those channels would go to infinite resistance and drop out of the equation. So given the human differences in response times after countdown to push buttons, may only have a few channels drawing current at any moment. But could ensure this by delaying the loop 200ms or so. I doubt they'd notice sub-half-second delay.Also considering auto-resetting breakers on each igniter channel. The delay would disappear when we call "Misfire!" and explain....let alone safe the pads and investigate/rewire.I was thinking a capacitor before the Arduino, to buffer the 5V. Definitely diode-limit the power coming in. The Arduino onboard voltage regulator is relatively weak....versus what we are switching here, in summer heat, in a box in the full sun, in the middle of a massive field... I've seen recommendations not to push the Arduino's onboard with more than 9V input.

author: LydaRA
author_rank: Contributor
timestamp: April 25, 2021, 10:50:26 pm
content: You recommended going with 12V relays...I know a lot of NAR clubs use big 12V automotive relays. Is this really needed to keep from welding contacts?Wouldn't a 5V relay coil let the battery last longer?I see a lot of pre-made 2/4/8 x 5V driver + relay boards. Are there common comparable 12V boards?Brand recommendations (on what seem to be a mass of Chinese-made offerings)? Thoughts as to which brands 1) fail least; and 2) might be around for replacements even ten years out?

author: themadhippy
author_rank: Super Contributor
timestamp: April 25, 2021, 11:13:20 pm
content: might want to put a key switch on the igniter power supply to avoid a suprise

author: ledtester
author_rank: Super Contributor
timestamp: April 26, 2021, 12:30:03 am
content: QuoteA lot of those Arduino relay boards have opto-isolated inputs and may be used with a separate relay supply source. See attached schematic:A resistor can be used to lower +12 V to drive a 5V coil:https://electronics.stackexchange.com/questions/322992/powering-a-5v-relay-from-a-12v-power-supply#

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 12:54:34 am
content: Indeed, there are other aspects not shown. The Pad Boxes will have a power switch with three modes:1) Off -- Self-explanitory2) Continuity Tests -- Powers only the Arduino for continuity checks. Absolutely no power to either the relay drivers nor to the igniters.3) RSO Control -- Powers the Arduino, and enables RSO Box commands to separately:a) Power relay driver boardb) Power to igniter supply busc) Power to individual igniters via relays.Nothing in the Pad Boxes directly commands a rocket launch.The RSO Box has to command the Pad Boxes to power up fully, and then to launch any particular rocket.But the RSO Box has no direct way to initiate the launch command. The RSO Box receives individual launch button inputs from each Scout at their own tables.So three different switches....many feet apart. A removable key to the RSO Box, with the RSO at all times....never inserted (in any position) whenever anyone enters the field (for setup, retrieval, or whatever). And an Arduino countdown clock that (while it can be started, paused, and reset) only allows launch commands during a two second window at the end of the countdown.And that's just the "systems" safeties. We have a lot more range discipline in the form of our range facility, policies, and procedures!

author: ledtester
author_rank: Super Contributor
timestamp: April 26, 2021, 01:02:17 am
content: QuoteWhat exactly is at the end of the long wires? Will you have long wires connected to digital input pins?

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 01:28:12 am
content: The long purple wires continue to the other boxes (RSO Box and additional Pad Boxes). Still working on what the command bus should be. I2C seems easy. Bandwidth needed is ridiculously low here (just replicating Continuity status and Launch commands....like two bytes each way). But there is a length concern, so may have to use RS485/422, ModBus, or such networking. But the the more we add, the more to build and maintain...The Scouts' launch buttons are directly wired to the Arduino in the RSO Box. I'm thinking a STP CatX from each set of four lights/buttons to the RSO Box. Cabling to be simple, cheap, and replaceable with whatever length desired.

author: phil from seattle
author_rank: Super Contributor
timestamp: April 26, 2021, 01:30:11 am
content: QuoteActually not. At absolute best it will draw the same amount of power as a 12V relay coil. In a given relay line a 5V coil will consume the same wattage as a 12V coil. The 5V coil will draw 12/5 more current. (P=IV, I = P/V) If the 5V power supply is a 100% efficient switcher both coils will consume the same power (watts). But no switcher is perfect so the 5V relay will probably consume more battery power than the 12V relay. And, if the 12V to 5V power supply uses a linear regulator, the 5V coil will cause 240% (12/5) the current draw as the 12V relay coil - most of it being turned into heat by the regulator.All this is a bit academic, though. Your relay coils, 5 or 12V, will be on for just a few seconds or less per firing and probably consume 5% of the total power consumption. Your igniters will take the vast majority - get the battery sized right for them and the relays will be fine.There really aren't any decent brands. I have bought a number of those relay modules and had some pretty bad luck with them - 5 and 12V. One 12V set I bought had 5V relays installed. They overheated at 12V and didn't work at 5V. grrrr. I generally make my own drivers because I have little faith in the Chinese relay modules. Best advice is buy several different ones and test the hell out of them. You may have better luck with 5V modules. Use what ever actually works.By the way, you might want to figure out how long it takes for an igniter to burn out. I was guessing 200 mS but worth running a little experiment.

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 01:41:10 am
content: Estes igniters seem to have a lot of variability. But that's one reason I'm wanting to dump 2A--get it over quick--instead of letting it smolder...

author: LaserSteve
author_rank: Super Contributor
timestamp: April 26, 2021, 01:55:13 am
content: I would exclusive-Or the IO pins to prevent inadvertent launches during microprocessor booting. God only knows what undefined states the chip can boot to. This just screams for a hardware watchdog circuit of some kind. That requires careful thought and testing.I will spare you the details of what happened when a fellow technician at un-named amusement park rolled his own pyro system interface to the show control system. That was way back when I was in college, but I have never forgot the lesson. I didn't get to see the whole barge launch several shows worth at once, but I'm sure the audience never forgot it.SOMEONE feel free to correct me if there is a better way to ensure a clean, event free boot.In the laser business we use arming keys that are not removable in the on position.Steve

author: ledtester
author_rank: Super Contributor
timestamp: April 26, 2021, 02:28:53 am
content: btw, if you're interested in making your own electric match + amplifiers you might check out this video:https://youtu.be/N3Hn9m183Q8

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 03:13:55 am
content: Indeterminate status during boot is one of my concerns also! Not wanting to hassle with a separate battery for the Arduino, but _cannot_ tolerate an uncommanded launch!One reason for the separate state in the Pad Box to power the Arduino before a separate state to power the drivers/relays.Also why I worry about making sure the battery doesn't sag on launches late in the hot summer day... Only a moment to launch each rocket, so only a few minutes total each day....kind of like the rare cold-cranking-amps load of a lawn mower...Maybe even AND the 5V/GPIO out of the Arduino to the power to the relay driver. So if the Arduino browns out, lock it out until post-boot?High-trigger versus low-trigger relays?

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 03:30:39 am
content: Unfortunately our policies & procedures will not let us use anything other than commercial model rocket supplies (and whenever reasonable purchased through BSA Supply Group). Just as with our shooting ranges, using commercial ammo runs up the costs a bit, however reduces volunteer labor and even more importantly shifts liability to that insurance.This launch control system, like our other facilities, can be hyper-scrutinized once....then just maintained. Big difference between a stable climbing tower, shooting range, etc facility versus ongoing pyrotechnical chemistry consumables. Yes the pool uses ongoing chemistry--but not something that should burn or blow up.Otherwise, yes, we'd press our own ammo reloads and rocket engines! Can be better product and more thrifty, but...

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2021, 04:13:38 am
content: Quote from: LaserSteve on April 26, 2021, 01:55:13 amI think I'd include a master relay that switches the entire 12V bus, a simple way to make this reasonably failsafe is to use a charge pump to couple an IO pin to the transistor driving the relay. That way the pin has to be toggling to keep the relay on, if it stops in either state the relay will drop out. It's the simplest way I can think of to achieve that, just a couple of diodes and capacitors driving a transistor that switches the relay coil.

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 05:28:54 am
content: I'm curious why you're involving digital I/O and Arduinos at all? Connect the igniters in parallel and driven from one healthy relay and that operated by a manual switch and be done with it. If you want reliability, skip the all of the cheaply made automotive parts and get atrueMIL specaircraftrelay and switches and use good commercial quality copper alligator or crocodile clips to clip onto the igniter leads. In my youth I launched hundreds of the model rockets and I used a automobile battery. Motorcycle batteries will work, if they're in GOOD condition and you're not firing too many rockets but for reliably skip them and just use a BIG battery. In my youth I carried a car battery several miles out to our launch site on my bicycle and it's not as hard as you might think. Today I would probably try 3 or 4goodquality Li-On 18650s in series. They're sure be easier to lug around and they can put out a real wallop.FWIW I have several aircraft relays made by IIRC Leech Corp and rated at 300 amps and the contacts in them are about 1/2" in diameter and about 1/4" thick and made of solid silver! They're rated to operate on 28 volts but work fine on 12 VDC. or you could use 7 3.6V LI-ON batteries to operate one. You don't need much current for the control circuit. Oh, here you go, this one is smaller but should be more than enough for your purposeshttps://www.ebay.com/itm/233804498650?epid=658228631&hash=item366fd586da:g:R6IAAOSwuwVfxrJC. Being both military and for aircraft use, these are seriously under rated! There are more on Ebay, just be sure that you're buying a real aircraft relay, a lot of them on there are just ordinary automotive ones. The first giveaway is the overall quality but then look at the screw threads. If it's for aircraft use it will have fine threads. If it's for auto use then the threads will most likely be course thread. Auto threads are also a much looser fit (Class) and won't withstand vibrations and are less reliable.One last piece of advice, if you try to power a digital system and the analog ignition system from a single source sooner or later you WILL have trouble! If you don't believe me go read up on the fire of the USS Forrestal in 1967. A switching transient in one of the rocket ignition systems on John McCain's aircraft (yes, later the US Senator) accidentally fired a rocket across the flight deck and into a fuel tank on another aircraft. If you insist on using some kind of digital electronics then use a completely separate power source for it.My last career in engineering was working on missiles for the US Army (Pershing, Hellfire and FAADS LOS Heavy), Canadian Army (ADATS), USN (SLAT) and finally on Brilliant Pebbles for the SDI program. I always enjoyed working with rockets and missiles!

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 05:52:47 am
content: Quote from: LydaRA on April 26, 2021, 03:30:39 amGeeze! If I was the BSA I would be much more concerned about the safety of a home brewed ignition controller than I would be about where you bought the piece of ignition wire! I can tell you from MANY trials, liberally in the thousands, that all of the ignition parts commercially made for "toy" model rockets is pretty much trash regardless of who made it. All of it is designed and manufactured to be as cheap to produce as possible without regard to performance.In my youth and in the heyday of model rockets, I bought igniters from Estes, Rocket Development Corp, Centuri and at least one other company that I don't recall. I always found the ones from RDC worked the best but eventually I just started using a single strand (22 gauge?) copper wire from a regular AC line cord. Nichrome wire sounds better because it has a higher melting point and will last longer in a heating circuit but abridge wire(the correct name BTW) is not a heater! It's intended to be used ONCE and only for a tiny fraction of a second and for consistent ignition timing it needs to heat up as rapidly as possible. Among other things, Nichrome has much higher resistance than copper so it will draw less current and won't heat as quickly or as hot as copper.And BTW it's probably not allowed by the BSA but I can tell you ways of getting much more consistent and faster ignition.

author: jonpaul
author_rank: Super Contributor
timestamp: April 26, 2021, 09:31:19 am
content: Bonjour, agree 100% with Stray Electron: Any use of CPU/Ardino/digit control for a safety related pyrotechnique is a terrible plan.The reliability and transient susceptibility is a big problem!EG Scouts are busy setting up the shots.The CPU/Controller has a bug or transient disruption: Premature ignition when scouts are handling the devices.What is the liability insurance in case of accident or death?See the old Scientific American Amateur Scientist columns of 1950s..1970s for safe amateur rocket practice with mechanical switches, key locks, interlocks on the firing circuit.SUGGEST TO DROP THIS RISKY ANDS DANGEROUS PLAN!!!Kind Regards and bon chanceJon

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 02:34:42 pm
content: The Arduinos would give us the ability to _embed_ more control of the process. With a small display on the RSO Box, we could even give speaking prompts (like PowerPoint speaker's notes). Looking towards that inevitable day....sometime I'll have to train my replacement. And if we lend it out to a district or unit....well, we can enforce some of the same range discipline.Going "smart" electronics also means that we can increase the distance between boxes and people--without having to worry about wire resistance. It would also speed setup and teardown--and keep down damage from children trying to walk through the "snake pit" of individual cables from the stock Estes controllers. Using common STP CatX or DMX connections would also mean whatever length of control cables can be sourced as cheap commodities at Walmart, BestBuy, wherever.I did consider "simpler" concepts, where the individual launch buttons and continuity lights wired directly and independently to the pads, using the RSO Box only as a relay interrupt on the master power supply. But that seemed to either need soooo many cables, or to require a Centronics or other less-than-common (today, impossible-to-find tomorrow) high-pair-count connector.Cables would then likely have to be custom made for each desired length.Still haven't worked out the Arduino to Arduino synchronization over these distances yet. And yet it seems "simpler" to maintain long term. Most electronics that don't fail in the first 100 hours run "forever." Cables drug around by volunteers in the field....well, they are just trying to help...

author: jonpaul
author_rank: Super Contributor
timestamp: April 26, 2021, 02:52:01 pm
content: cables and connectors of every guage and conductor count are easily available at DK, Mouser or epay.Any digital based CPU is subject to transient and other issues in a system like a firing range.Jon

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 04:10:06 pm
content: FWIW If I were the BSA I would never allow you to use a home designed and built launch controller in any of my events regardless of the bells and whistles that it includes, PERIOD!Everything benefit that you have named could be accomplished on a traditional style launch controller controlled by manual switches and not controlled by some kind of uProcessor."length of control cables can be sourced as cheap commodities at Walmart, BestBuy, wherever."If you insist on a controller like this then go buy one of the commercially built firing boxes that are made for use in pyrotechnics (i.e. Fireworks) shows. They have the ability to synchronize to music and other external events and are designed to handle up to thousands of firing circuits.Designing a launch system, particularly one that is intended to control multiple simultaneous launches, to use cheap Walmart-grade components is the worst idea that I've heard so far today!

author: jonpaul
author_rank: Super Contributor
timestamp: April 26, 2021, 05:15:23 pm
content: Agree 100% with Stra Electron,The liability in case of injury or death is virtually unlimited in our litigious society.STRONGLY suggest to use ONLY commercially available and approved firing systems and NOT DIY.This is NOT "rocket science" ... here is the circuit!Battery...fuse......master safety key switch ....master bus...individual firing switches ....cables ....rocket ignitors.Bon Chance,Jon

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 06:00:03 pm
content: As has already been said, there are _MULTIPLE_ power disconnects involved before ANYONE (Scouts or adults) are allowed on the field. If it is safe to wire up a rocket while the stock Estes controllers sit on the table, but the removable keys in my pocket at the pad--then how is it unsafe for this proposed system to sit disarmed with the removable keys in my pocket at the pad?And if someone is dumb enough to flip the power switch to the Pad Box at all, then the strobe and siren go off. Show me how a stock commercial control gives that warning?We have electricians in our Council. We have been consulting with the local NAR and Tripoli chapters. Seems like a launch control system can be as well safety-reviewed before acceptance in the same way we commission professional review of our climbing towers and COPE elements by authorities in that field.If I were going rogue, I wouldn't be taking the time to ask for other opinions on even the simplest of electronics that I learned as a 13 year old Red Cross volunteer building motor wheelchairs and handicap adaptations. "The only dumb question is the one that goes unasked until _after_ something goes wrong."But thanks to all for your concerns....and even more for any and all _constructive_ guidance shared.

author: jonpaul
author_rank: Super Contributor
timestamp: April 26, 2021, 06:20:55 pm
content: Perfect, good luck....Check liability insurance (:-:)j

author: LaserSteve
author_rank: Super Contributor
timestamp: April 26, 2021, 06:30:51 pm
content: Take lessons from the elevator design folks and the railroads, who use failure resistant relay logic in such a way that springs and gravity in the relays take things to failsafe states. It is OK for the processor to enhance the event with audio, warnings etc, but final launch authority should come from the ladder logic. If you have your hand on the dead man's switch, it is OK for the processor to close a final launch relay after the countdown, provided you have a full field of view. . Odds of a powered up processor failing in a 10 second countdown are low if it has demonstrated to you in some way that it's program is running before you trust it and manually gate it into the circuit. Odds of it failing indeterminate at startup or just setting there in the sun are high out in the field. Odds of it being latched up from conducted EMF from the coil of a large relay or a two way radio are are high for example.I'd also read up on the concepts of "Cockpit Resource Management", if I were writing the launch procedures. You'll see why in a minute.In my day job I'm senior technician for a large portion of a university. I'm also an Eagle, class of 1988. My rocketry days are long ago, but I still remember the basics.This is where I state I'm not a licensed Professional Engineer in the State of Ohio, nor anywhere else in the world. I'm just an old technician with lots of experience. My advice is just that, advice, and it is only worth the electrons it is transmitted by. There is the required disclaimer.So lets more or less define what the CPU is going to do for you. Then we can proceed. Does the processor select which rocket will launch? We are firing one at a time, not a Salvo?How are you going to test if an ignitor is properly hooked up? Ie the well designed Ballistic Galvanometer function used in blasting..What else do you intend for the microprocessor to do?Would it not be more appropriate for the processor to characterize the flight, ie show the potential effects of the prelaunch wind, predicted ballistics , measure time of flight etc? Just throwing out the idea of other uses that could enhance education.One other thought. If I were doing this, the Launch Safety Officer would have a firing handle in his hand as a dead man's switch, and the Scout would have a firing handle in her/his hand* for the actual firing. The Scout then has a launch checklist, as does the safety officer. They have to concur to launch and both turn keys before the scout activates the trigger switch. . The Scout's firing switch could activate the CPU for the countdown, warnings etc, but the LSO's firing handle is doing the safety functions and made the final decision to energize the interlock relay(s). (*Scouting is Co-Ed now in the US)BTW, "Fire" is not a valid command, nor should it be used. See the last scenes of " The Bedford Incident" movie on Youtube. Lots of learning opportunities here for the scouts as to the "how and why".I was going to avoid mentioning the rocket incident on the carrier, but it did cross my mind.Steve

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 07:23:40 pm
content: Quote from: jonpaul on April 26, 2021, 05:15:23 pmI agree. One of the first things that I learned and one of the most important was "KISS", "Keep It Simple, Stupid!".That's a Golden Rule when it comes to safety critical circuits. Everything that you add to the circuit lowers reliability and is an added safety risk.You can use optocouplers and added contacts on the relays (and separate power supplies) to operate any bells and whistles but the basic control circuit should be keep as simple as reasonably possible.One of these days I'll have to tell the story of how one of my coworkers nearly got crispy-crittered while test firing a Bomarc missile! Long story short, he was standing behind one when it ignited prematurely. He jumped over a safety barrier and wasn't badly injured but got scorchedrealgood!

author: Stray Electron
author_rank: Super Contributor
timestamp: April 26, 2021, 07:39:13 pm
content: Quote from: LaserSteve on April 26, 2021, 06:30:51 pmThey make MUCH better ones today. I own a 4314 Digital Ignition Tester made Vahalla Scientific. It's basically 4 wire Ohmmeter that is guaranteed not to output more than limited amount of current. I don't remember the numbers but in the microamp region. OK, I had to go look it up, the test current is 10uA in the standard version.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2021, 07:42:02 pm
content: Quote from: Stray Electron on April 26, 2021, 04:10:06 pmSeems a bit hyperbolic I think. We're talking about model rockets weighing a few tens of grams here, not armed ballistic missiles or sticks of dynamite. It's important to be safe, but you don't need to go overboard. I remember the official Estes launch controller I had when I was a kid and it was nothing more than a cheap molded plastic housing with a leaf switch pushbutton molded into it, the "key" was a metal wire that when poked into a hole, bridged a pair of contacts. A small incandescent lamp wired across the button served to indicate the system was armed and had a complete circuit. Some of us didn't even have the proper launch controller and we got by using a bundle of cheap speaker wire and just touched the ends to the terminals of a 6V lantern battery to launch the rocket. All this talk about mil spec switches and aircraft relays, come on, the official systems that have been around for decades are built like cheap kids toys, they *are* cheap kids toys. As long as people are following reasonably safe practices, an uncommanded launch is more of a "whoops!" event, not "OMG call 911 and bring in the FAA accident investigation team and the ATF!". Let's keep things in perspective here.

author: jonpaul
author_rank: Super Contributor
timestamp: April 26, 2021, 07:57:56 pm
content: What exaclty linits the rocket charge when used in the proposed igniton systme?Could they try larger and larger rockets over time?Can the grains of propellent be linited to <10 or migh it be 50g? 500G? 5kG?Regardless of size the use of a pyrotechnic propellant can always cause injury.j

author: Syntax Error
author_rank: Frequent Contributor
timestamp: April 26, 2021, 08:11:04 pm
content: Cool projectI would add a loud claxon. One that indicates to the whole field that therange is hot. Or safe. This could be any electric claxon or even a scavenged truck horn.The claxon canonlybe operated under the command of the designatedRange Boss- who has a hivis jacket with that on. Andeveryonedefers to the Range Boss.Also, a GoPro camera on the launch pad to film the rockets launch in closeup. Which is going to look cool on YouTube for your public outreachHappy firing.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2021, 08:12:23 pm
content: The engine sizes readily available to hobbyists limit it. Most of them come in 4 basic sizes, A, B, C and D, with a range of thrust and ejection charge delays for each. There are larger engines which are available to serious hobbyists but you won't find them in the average hobby store and they are used by a whole different group of people.Bottom line is the official launch controllers that are sold alongside the rocket kits are cheap toys. They're built with the quality of a 99c trinket from China.https://estesrockets.com/product/002220-electron-beam-launch-controller/https://estesrockets.com/product/002221-astron-ii-launch-controller/There are also rules and regulations, they limit the weight and materials the rockets can be made of (no metal, no sharp edges, etc) and mandate using off the shelf engines, no homebrew stuff. These are kids toys, I remember building several of them when I was age 8-14 and launching them with my friends in a vacant lot near the house I grew up in.

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 09:03:51 pm
content: Cool idea. Some parent in the group often uses a smartphone to film launches for their child/den. We should get the film for camp use.Similarly, we launch once and wait for "all down," & "range clear" commands. Then we ask each Scout to stand with their rocket where it landed. We call them a "living scatter-plot." A chance to discuss more math, science... "We all started on the same rods, pointed the same way--why did we end up scattered across the field?" "Since the winds above the treeline pushed us left, let's point the next launch a little more to the right." Then we reload and launch a second time. Then compare where the plot has everyone standing this time. Reinforce the safety with "We corrected our aim, but still don't control winds aloft. Most importantly, even if not dead-centered--do you see why we rope off such a LARGE roped-off range (much larger than Estes calls for)--in an even larger open field?" I keep a log count of on-range, off-range, & lost (gust can sometimes put us into trees). And can confirm despite hundreds of launches per day, we can usually count the "lost" on one hand! That's better than many NAR/Tripoli launch days!Anyway, would _LOVE_ to get photos by drone or such of the "living scatter-plots" to send home souvenirs to help the children remember the lessons. We let them take home their rockets (minus engines)....but that's a thing. Let's give them a selfie!

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 09:07:36 pm
content: Yep, each Pad Box will have a local buzzer and flasher to warn of power on the igniter supply bus.And the first Pad Box will have a pike with a larger strobe and louder horn. Warns the whole field of countdown initiation. (Kind of like the pike on copiers to let the entire office know a customer order may have just been faxed in to be handled...)

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 09:18:41 pm
content: Yep. We have been using the stock Estes controller safely for years. This will be even safer, yet increasing throughput. The _only_ way I'd increase throughput is with increased controls!And indeed, _policies_ help. As said before, like our rifle, pistol, shotgun ranges....we do not allow ammo brought in from outside. The camp provides our known & proven choice of ammo. We have only ever flown A and B engines--and usually just 1/2A!The Scouts build their rockets. But they only observe as the range staff load the engines ourselves. Neither the ready engines nor the used engines ever leave the range and RSO's control! Ready engines are kept locked in an ammo can until actually being loaded. Spent engines are collected in a large pail of water and stirred to dissolve to inert any remnants. (Yes overkill, but we are modelling responsible behaviors.)

author: Gyro
author_rank: Super Contributor
timestamp: April 26, 2021, 09:20:52 pm
content: Insurance issues aside, I'm actually heartened to find somebodytryingto do it properly - certainly compared to rocket launcher project threads that have come up in the past.

author: LydaRA
author_rank: Contributor
timestamp: April 26, 2021, 09:45:32 pm
content: Thanks, Gyro!The year before I took over the rocketry range, I was just an observer with my fourth grade son. Although I was already a shooting instructor and on my way to formal NRA RSO. But I was an observer, so _tried_ to hold my tongue and let my child learn from another volunteer... That is _UNTIL_ the guy left the launchers' removable keys on the table by the launchers--and the Scouts--as he went out to the pads and started rewiring?!?!? I _HAD_ to shout out to my boys: "Sit down at the back of the tent. We are not blowing this guy's fingers off. He is literally wrapping his fingers around gun powder to setup your rockets. There will be no excited little fingers fidgeting with either the controllers or the safety keys."After that session, I excused myself to go talk with a Shooting Sports Committee friend. We agreed that although rocketry was not under Shooting Sports in the national guide, NAR and common sense says rocketry should run with the same discipline as any other range! They backed my play, and the volunteer was reassigned to a station better suited to their temperament. That night, SIX of us (Camp Director, Program Director, Quartermaster, Shooting, an Electrician who ran rockets in years prior, & myself) and a Scout all met to re-enact and re-imagine how the station should/could run. We looked at field (other stations or campsites adjacent), facilities (tents, roping, red flags, etc.), equipment (controllers, keys, rods, covers, etc.), range countdown & commands, educational speaking prompts....ALL of it. We then played RSO & Scout participants, and acted it all out start to finish until ALL were satisfied.I have been running the station in the years since. Still enjoying what everyone had to contribute, still "paying it forward" to the next generation--and still insisting upon God's own discipline on my range! "I've never had to meet a Mom with their child at the ER--and I'm not going to start today!"

author: Stray Electron
author_rank: Super Contributor
timestamp: April 27, 2021, 12:16:27 am
content: Bravo for you. It's good to see someone that still takes the time to teach boys how to use guns and some life skills in general, particularly in an organization like the Boy Scouts that has taken so much public abuse in the past few years. Scouting and model rocketry are both about dead in this area. I tried to get my son into scouting some years ago and basically we had to start our own troop with no guidance or help from the BSA. None of us really knew what we were doing and it soon fizzled. The few scout troops that are left in this are don't do any camping or anything of that sort, they've all become Social organizations that have food drives for the poor, visit nursing homes and other PC events. My BIL was a scout master for an out of town troop and I found some good camping gear including a NIB gasoline fueled Coleman camp stove and I tried to donate all of it to his troop and I was prompted informed that his troop didn't Go camping! And that the BSA do not allow their scouts to handle anything with gasoline! I bought model rocket kits for all of my nephews but no one was really interested and I don't think that any of them every built any of them. America will soon be a non-technical country from everything that I see with today's youth. My son is the same, he's now in his mid 30s but the ONLY thing that interest him are computer games! He literally has NO life away from a computer and he has ZERO technical skills.

author: wizard69
author_rank: Super Contributor
timestamp: April 27, 2021, 12:28:26 am
content: I somewhat agree with others, this seems like going overboard and a liability issue. This especially if nobody on the team has an engineering background. However I have no idea how the BSA are insured. You might have coverage if something goes wrong or you might not, I’d ask for an answer in writing. In the end when it comes to their kids parent always look for somebody to blame besides the kid.Now all of that being said, a little over 45 years ago I built my own little launch station for model rockets. A side thought is that this could be very educational all on its own. In any event except for the housing almost everything was salvaged from something and due to money I keep it simple.In my case I ran it off a tractor battery as that could be driven to a near by field. Some things to consider:1. The wire used to set off the igniter is basically expendable and will often be destroyed at blast off. Effectively you want the igniter wire to get hot very fast so you want to assure low impedance throughout the power circuit.2. Low impedance is good but there is a catch, your alligators can short at launch and this can be bad if you don’t have some sort of protection. A lead acid battery can supply hundreds of amps making a mess of your project real quick.3. I seem to remember having a method of checking continuity, but that was so long ago I don’t remember how I did it. It had to be simple though because I had little to work with.4. A decent auto supply store will have some of the hardware required. Jumper cables can supply you with battery terminal sized alligators, fusible links or standard auto fuses and sockets. Not to mention relays, switches and other parts. Of course you can go to an electronics supplier like Digi-KeyThis post is putting me into a bit of a funk as I just realized I have no idea what happened to that launch controller. However I remember it being absolutely fun to build. Fun is one reason why I think it would make a great project for Boy Scouts and of course you learn a bit. You still have the liability issue so considering the other activities scouts engage in there must be a way to a BSA approved launch controller. Considering the educational potential you would think that a national level solution could be had.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 27, 2021, 01:30:49 am
content: Perhaps a good design for a rocket launcher kit would be based on actual explosive triggering equipment? Basically a generator with a mechanism to spin it using a handle and a switch to dump the energy of the spinning rotor all at once:It's hard to imagine any fault that can cause an unwanted activation aside from someone operating the unit when they're not supposed to, but that can be prevented by adding a provision to lock the handle with a padlock.

author: LydaRA
author_rank: Contributor
timestamp: April 27, 2021, 02:37:47 am
content: As I have alluded to above, this will be well-reviewed before accepted into camp use. BSA insurance covers us as long as we stay within guidance. For Rocketry, BSA defers to NAR for guidance. I have already opened discussions with the local NAR chapter, and reviewed their local equipment. They use a custom control system built somewhat similar to my proposals: from custom PCB (although not Arduino), commodity cables (CatX & AC extension cords), car battery, and high-power relays (automotive). So our liability should be covered by the same as how we have climbing tower, pool, etc inspected by authorities in their fields.I would hope that this might become a prototype for others to use, across BSA and elsewhere. (Same as how our local COPE & Climbing Standard Operating Procedures are good enough that they are studied, referenced, and spread by the larger BSA.)

author: LaserSteve
author_rank: Super Contributor
timestamp: April 27, 2021, 04:47:32 pm
content: I'll do a rough schematic drawing this evening.Steve

author: LaserSteve
author_rank: Super Contributor
timestamp: April 27, 2021, 04:59:40 pm
content: Affordable modular switches come from here:https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/22mm_plastic#You select the switch body, the actuator and the modular contacts for "build a switch" . We use 22 mm bodies at work as they are student proof and ultra reliable. Their 22 mm high brightness blue and green led indicators work in a fairly bright room, with day light streaming in. . They will also custom print you the key legends for cheap.McMaster Carr also has nice modular switches.Don't forget the "missile switch" switch guard for arming toggles:https://www.sparkfun.com/products/9278We do use the above at work as well. There are many vendors.We like the "twist to release" style of E-Stop:https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/fuji_electric_22mm_(ar22_series)/emergency_stop_pushbuttons_illuminated_-a-_non-illuminated/ar22v0r-01rSteve

author: wizard69
author_rank: Super Contributor
timestamp: April 28, 2021, 04:00:59 pm
content: i remember those days and for an independent launch of a single rocket I agree 100%. the problem is that this isn't a back yard event and more so there is the desire to add automation to the launch. Not one rocket but multiple rockets, all of these things require rethinking safety.Personally I'd rather see a roll back of what is being attempted here. The goal is to get scouts involved to have fun and learn a bit. That can be done via a build of ones own launch controller. Why there is a need to do a multiple rocket launch controlled electronically is beyond me.Quote from: james_s on April 26, 2021, 07:42:02 pmActually you are underplaying the risks in these "toys". Toys in quotes because they are in every sense real rockets and thus have all the risks associated with rockets. Maybe on a much smaller scale but a burn from a model rocket can still send you to a hospital and even a accidental collision with a model rocket can cause injury.It is sort of like flying model helicopters. They can be perfectly fun but fly those rotor blades into your neck and you are dead.In either case though the big factor here is that the BSA is an organization and is the constant target of lawyers and parents that are overly protective of their children. Believe me there are parents that are just waiting for a reason to bring a law suit against the BSA. They will do that for just about any reason even if the only impact on their children was a scare from an accident.Now I can't say I agree with this mind set, I think it is fair to say my parents where the opposite of overly protective. If you where bleeding you learned to patch your self up and if sprained you walked it off.

author: wizard69
author_rank: Super Contributor
timestamp: April 28, 2021, 04:29:17 pm
content: If you have these contacts; I'd work with the NAR and BSA to create a standardized and tested solution for all Boy Scout locations. Get the design reviewed by qualified engineers and maybe even industry functionaries (such as Estes) that can point out any short comings that may exist. If there must be programmable devices in the hardware have somebody familiar with safety systems design it and program it.I'd even consider trying to get industry involvement in the launch controller. There are still industries that will be willing to support the BSA and it never hurts to ask. In that regard you might be able to get some donations of either hardware or code. It would be nice to have everything implemented on a safety PLC for control logic and the rest mounted in a well laid out industrial panel. Again the goal is to have something that can spur the interest in scouts. In the end there are as many or more jobs in automation available to scouts as there are jobs in aerospace and frankly right now there is a shortage of engineers and technicians in industry. So you might find an industry leader that wants to spur interest in youngsters.By the way, part of the reason I'm concerned about software is that if one doesn't have the right background, programming can introduce faults that might not be easy to find and stay dormant for years. Just yesterday at work I had a machine dong very strange things due to a combination of hardware and software that was not seen in the prior 10 years.Quote from: LydaRA on April 27, 2021, 02:37:47 am

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2021, 08:27:37 pm
content: Quote from: wizard69 on April 28, 2021, 04:00:59 pmI disagree. I was into model rockets for several years up until I was around 15, it was something young kids did, mostly with little supervision. When I was in 7th grade my middleschool had a "airsports" elective and the class projects were a model rocket and a rubber band powered balsa/tissue airplane. We built them in class and then had a launch day where we shot them off from the parking lot and collected them from the athletic field, mind you this was while physical education classes were simultaneously using the field. In the ~20 years that class ran before the teacher retired I don't think there was ever an injury, we were all taught basic safety and nobody got near rockets that were on the launchers ready to go, it wouldn't have mattered much at all if one had launched inadvertently. It just isn't that big of a deal, sure it's possible to get hurt by one, but far more kids were hurt playing sports and nobody is advocating mil spec body armor to play soccer or lacrosse.

author: LydaRA
author_rank: Contributor
timestamp: April 28, 2021, 09:42:15 pm
content: If you didn't take away from what I said above, we agree: safety trumps all on the range.So which is more safe: trying to account for SIXTEEN loose launch keys, or ONE Master key?I am human, and _have_ had to halt movement to the field, when I realized I had missed collecting a key. With the RSO being at the table, no one could have inserted that key. But it was a breach, and safety modelling _required_ we immediately halt and reset. That was with just ten separate keys. And any RSO will still be human, so still subject to mistakes.Thus I have _zero_ interest in expanding the number of individual loose keys & controllers to keep up with. It just increases the odds of failure. But in my proposed system, just as in the U.S. nuclear missile systems, there are TWO removable keys in the hands of TWO different people for any launch! I "only" have to remove the RSO's Master Arm key to safe the entire range--each and EVERY rocket at once.And if I forgot to remove the RSO's key, what are the chances an excited child--eager to control their own launch--would forget to remove their key? First consider that ZERO launch keys are handed out until AFTER the first round of rockets are completely wired up--and EVERYONE has left the range! The keys are in the ammo can with the engines--at the pads... So appreciable risk does not occur until correcting first-round misfires or wiring up for the second round.We could even make the ammo can require the _same_ key as the RSO's Master Arm! So one could not pull out the engines for the misfire or second round, without _first_ removing the key from the RSO's Box!MUCH better than relying upon a bunch of loose OEM "keys." Let's get real, the OEM keys are just metal pins. When we have broken/lost one, we made replacements by bending simple landscaping pins! So imagine how "secure" it really is, when so many children have metal picks in their pocketknives... Do you understand why we always keep a responsible adult at the table to oversee the controllers--even after we collect the "keys???"Better safety _CAN_ be built into even a "more complex" system!

author: LydaRA
author_rank: Contributor
timestamp: May 11, 2021, 09:36:10 pm
content: Trying to learn KiCAD....still rough, but getting better. Finally enough drafted to share (and drown in the red ink as you all mark it up)... Thanks in advance for constructive criticism!Showing just two of eight independent parallel igniter sub-circuits. And considering variations....DPDT vs. SPDT....Arduino source current for continuity measurements vs. dedicated constant current source....building driver/relay sub-circuits vs. buying an 8x driver/relay board...Obviously just focused on the pre-launch continuity tests and one the launch signal handling. There _ARE_ _MULTIPLE_ power discos, removable keys, momentary "deadman" switches, and program logic safety measures as well!

author: LydaRA
author_rank: Contributor
timestamp: May 11, 2021, 09:37:11 pm
content: I think I prefer an isolated source of a constant "flashbulb safe" current for the continuity tests. Seems safer and frees pins on the Arduino. However there are a variable number of rockets to be launched, from eight (initial "drag race") down to possibly just one or two (after replacing igniters, re-clipping leads, correcting whatever misfires...). So with variable number of parallel paths, seems each continuity test sub-circuit will need its own low-voltage/low-current power source. Right? Any suggestions for a part number (I stuck in something representative, but KiCAD had just VAC chip....but yes, wrong item for this)?Still think we'll need some sort of amplification to distinguish the three resistance levels on the igniter...

author: ttx450
author_rank: Regular Contributor
timestamp: May 12, 2021, 12:26:16 am
content: each rocket is a cue, does not matter for elc compliance maybe how you wire it. I built a capacitive discharge firing system, that easily fires 12 in series at a 1/4 mile. 1 elc ign can draw a lot when latched and will burn out switches. I dont recommend for model rocket firing. simple 12v battery. I did not read the whole post. if you need safety all go no go ck continuity ck, let me know and I'll see what notes I havein commercial use the firing system account for resistance, by selecting amount calculated.. model rockets, you dont need to worry.. just 12v & safety ckif you wire in parallel, good luck.. use nails and 12v car battery.

author: LydaRA
author_rank: Contributor
timestamp: May 12, 2021, 01:26:21 am
content: Quote from: ttx450 on May 12, 2021, 12:26:16 amThanks, but I cannot imagine even trying to get that through the BSA's Program Hazards Analysis. Letting fourth and fifth graders dead short a car battery with nails cannot possibly be safer than even the sad OEM launch controllers.

author: LydaRA
author_rank: Contributor
timestamp: May 12, 2021, 04:32:00 pm
content: Updated schematic... Thoughts?

author: ledtester
author_rank: Super Contributor
timestamp: May 12, 2021, 06:06:42 pm
content: Some questions...About the resistors around the MOSFET gate... any reason not to put the the 100K pull-down in between the 100R and the gate?It seems you have a buzzer in series with the igniter. What kind of buzzer are you using?It seems that the continuity circuit is always live. I realize there are resistors in place and you'll have other fail-safe measures, but the idea of current running through the igniter while I'm handling a rocket is a little unsettling.

author: LydaRA
author_rank: Contributor
timestamp: May 12, 2021, 09:09:53 pm
content: Quote from: ledtester on May 12, 2021, 06:06:42 pmNot that I know of. Lesser ground to the Arduino pin or to the FET pin? Why?Quote from: ledtester on May 12, 2021, 06:06:42 pmYes, not really. Gotten a lot of push back on this. My intent is to have a passive, "oh shit back off" warning that the igniter cable has current, should the relays weld (or anything else fail) that would put someone coming to the launchpad at risk. But also don't want it to pollute the already tough Continuity Test measurements. Suggestions?Quote from: ledtester on May 12, 2021, 06:06:42 pmOh the fun of partial diagrams... :-p Each Pad Box will have a power switch as the first thing to "safe" when entering the launch pad area. Seems wasteful to power the continuity test even when not reading the Arduino analog gins....especially when running this all from limited battery in a field w/o grid power available.

author: LydaRA
author_rank: Contributor
timestamp: May 13, 2021, 12:03:30 am
content: Updated (still partial) schematic... Thoughts?

author: LydaRA
author_rank: Contributor
timestamp: May 15, 2021, 11:13:06 pm
content: Getting further along with KiCAD....added more of the safety mechanisms I've discussed, but some people cannot seem to grasp. More functionally complete, but I am sure just that many more errors in resistance calcs and component choices...For the love of God, how does one get KiCAD to differentiate two different bus levels (12V vs 5V)? And how does one generate a PCB, when _so_many_ components I or others reference do not exist in the library?I'm running out of time. Any help marking these up is GREATLY appreciated by both myself and the not-to-be-disappointed Cub Scouts!

author: ttx450
author_rank: Regular Contributor
timestamp: May 17, 2021, 01:37:05 am
content: Quote from: LydaRA on May 12, 2021, 01:26:21 amuse a bunch of switches? why make it so complicated? if you have a e match that fail to burn though can cause a latch, then more current draw. yes it could burns things out depends on how you make it. I know of commercial systems made to run on battery 12v.I will not share a cap discharged system, much more dangerous for you and the kids.

author: LydaRA
author_rank: Contributor
timestamp: May 17, 2021, 02:06:19 am
content: Quote from: ttx450 on May 17, 2021, 01:37:05 amLet's see... The OEM controller has one person (Scout/LCO) with possession of a removable plug/key/switch and a momentary button--at a mere 17 feet from the rocket burn. That's it for OEM safety.I've designed to still keep a removable "key" for the Scout/LCO. But now it is a true key, with rejection & fault alarm features! The Scout/LCO's momentary Launch button is now under a flip-cover. Added safety, with....OMG, the "complexity" of lifting a cover! And then I've mirrored these same _common_ safety measures with a RSO position....a second removable (real) key, and a flip-covered momentary switch. But yeah...."oh so complicated"...."who could even understand how to operate it?" Let's see, maybe anyone who has ever watched a movie where two men have to agree to launch the missiles?And we can do this with the NAR-prescribed safety of 300 feet of communications cable between the Scouts and the rockets burning. Heck, at truly safe distance, bring on a full-fledged CATO for awe & inspiration!..Well, thanks anyway for the contribution to the efforts to inspire the children...

author: ttx450
author_rank: Regular Contributor
timestamp: June 06, 2021, 11:47:10 pm
content: Quote from: LydaRA on May 17, 2021, 02:06:19 amgood luck I know many commercial companies that use straight 12v battery. I been doing this prob longer then you been alive.