RC Multi Rocket Launch Ckt (Questions)

Discussion in 'The Projects Forum' started by Rent2Own, Sep 2, 2011.

  1. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    Main Components
    *Radio Controlled Receiver
    *4017 decade counter
    *Estes rocket igniters
    *A diode & transistor per active 4017 output pin.
    *One resistor downstream of all transistors to limit the high "launch" current.

    Operation
    Single pulses from the RC receiver, actuated by RC transmitter, are sent to the 4017 counter. Per received pulse, one 4017 output pin at at time will be active high turning on the downstream transistor.

    This "switching", & now "on", transistor will complete it's isolated launch circuit. This isolated launch circuit will be, for example, 9V battery to X0 (Estes rocket) & finally through the R1 ("launch current" limiting resistor) & ground.

    The next pulse from the RC receiver will, by operation of the 4017, 'active high' the next 4017 output pin repeating the process until pin 6 is active and loops to the reset pin of the 4017.

    Notes
    -I am calculating R1 from Estes rocket amperage requirement, 9V battery internal resistance, & the transistor's max rating.
    -I haven't chosen component values since I still have questions about the circuit design in general.
    -I plan to add two safety cut off switches - one on the vehicle and one in the transmitter channel used.

    Questions
    *Is a "pull down" resistor needed somewhere between the RC receiver and Clock input pin of the 4017 to eliminate "floating"?
    Should I tie all other unused 4017 pins to ground?
    *How do you determine the supply voltage to the 4017 counter? (Manufacturer data sheets?)
    *Are the diodes needed?
    *Should I have a fuse with R1 to protect the transistors?
    *Are there any major flaws in this circuit?


    This is for a RC, tracked, rocket launching vehicle.
    Any advice is appreciated and thank you.
     
    Last edited: Sep 2, 2011
  2. SgtWookie

    Expert

    Jul 17, 2007
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    First, I have a big problem with the radio controlled portion. The mere fact that you purchased a radio receiver means that you are willing to receive spurious transmissions from sources that were unintended to activate your receiver. Even if you have a fairly long code sequence that has to be transmitted in order to "unlock" the receiver, there is still the chance that a purely random burst of interference will cause unintended activation of your receiver. The activation of the receiver may cause unintended firing of the rocket motors, being a hazard to any persons remaining in the vicinity of the launch pad.

    You do not seem to have planned for any safety device, which is a glaring oversight. There needs to be an arming key, which the person connecting the engine(s) to the ignition source carries with them to the pad. However, with an R/C ignition system, you eliminate a couple of safeties from the system - which is simply not good practice.

    The 4017 won't source enough current by itself to saturate a transistor with one of those Estes igniters. You'll need over 1A to get the igniter hot enough to fire the engine. A 9v battery might work for a couple of ignitions, but that's about it. You really should use at a minimum eight AA batteries in series to get 12v; you will have far more power available for reliable ignition. Radio Shack sells an 8-AA pack for a few bucks. You're better off yet with a 12v SLA/VRLA/AGM battery.

    All the diodes do is drop voltage.

    You don't want a resistor to limit the "high launch current" - you want that igniter to burn hot as it can for a few moments.

    The way you have wired the RESET input will not guarantee that the 4017 will be properly initialized on power-up; so you may have multiple simultaneous ignitions when power is applied.

    BTW, I'm not new to Estes rockets. I started building them back in 1965. I was a missile systems/fire control technician in the Marines. I've spent many years in the general field of aerospace since then.
     
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  3. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    @SgtWookie

    Hey. I've read several of the "rocket launching" threads on this website & was hoping you and two others, specifically, would give some insight here. I realize you know what you're talking about, in other words.

    Well, I just developed this circuit today and posted it to find out the "glaring oversights" you've mentioned. So it's not like it was intentional. I edited my post before you replied to inquire about & add safety features.
    ----------------------------------------------------------
    *Although there's hardly anything I could do to combat spurious interference, as you've pointed out, I would like a safety switch on both the transmitter (for the launching channel?) and on the vehicle (so there's no power from the launch circuit battery).

    *I'll remove the diodes then.

    *Wouldn't my R1 protect the transistor from the high launching current and just make the ignition time take longer for the rocket? (Or can the transistors handle it?)

    *Should I leave the 4017 reset pin to ground?

    *So i'll up the rocket circuit's battery to 12V. You're saying the 4017 won't saturate the transistor & ignite the rocket, but I only wanted it to saturate the transistor and then the 12V supply would do the launching. Is this good to go now?

    Thanks a lot for the fast reply.
     
  4. SgtWookie

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    Well, myself, Bill_Marsden and a few others have been involved in stuff like that for more years combined than we probably would like to think about. ;)

    I see. Well, the reply I made was just an "off the top of my head" quick review, and not especially thorough - just touched on some of the basic main concerns.

    Perhaps you didn't understand me.

    A hobbyist-constructed RF remote cannot be made safe enough for use in a rocket engine igniter circuit. Even commercially available rolling-code receivers can occasionally be unintentionally activated by spurious RF emissions.

    There has been a recent well-publicized incident of this occurring when a USAF installation out in Colorado brought a high-power radio transmitter online, which caused the random activation of thousands of neighboring residents' garage doors, and a rather large public outcry.

    Since the safety of such a device cannot be guaranteed, I will not entertain further discussion of using an RF remote for the project.

    The activation control aka "launch panel" must be connected to the launch pad by wiring.

    The resistance needs to be on the base, not the emitter.

    However, the base current will not cease, even when the igniter burns through, as the 4017 output will still be high.

    The 4017 reset must be raised momentarily on power-up to set the counter to a known state (ie: only Q0 high, Q1-Q9 low).

    The 4017 won't supply enough current to saturate a bjt (bipolar junction transistor); it might output ~20mA tops if it's going downhill with a tailwind and the Devil himself chasing after. In order to saturate a BJT, the base needs to be supplied with 1/10 of the desired collector current. I don't remember offhand the current requirement for a 12v driven igniter, but for simplicity's sake let's say 2A @ 12v for ~100mS. 2A/10 = 200mA, and you have less than 1/10th of that available.

    Additionally, since the 4017 always has one output high, your base current will continue to flow as long as one of the outputs is selected. This means you will be wasting a fair amount of power after the first ignition occurs until the power is turned off.

    Why don't you use an existing schematic that works, instead of attempting to design your own?

    You just happened to luck out. This forum is not interactive; it can sometimes take days to get a reply. Some topics never get answered; as there are LOTS of people with questions, and relatively few with time and knowledge enough to provide answers.
     
    Last edited: Sep 3, 2011
  5. Wendy

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    Mar 24, 2008
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    I'm not clear about something, it may have been stated and I missed it. Are you trying to sequentially launch multiple rockets, or are you trying to cluster several engines in one model? Clustering was my bane, I finally found a technique that worked for me, then dropped out of the hobby, and the tech has changed under me where I'm back to square one. The big thing was it used flash bulbs and Centari ignitors, which had a brown pyrotechnic material that acted a lot like a fuse. I read where they clustered 27 engines at once with that technique.

    I tend to agree with earlier discussions that suggest solid state isn't the best way to go, as the chaos of a launch it is possible to have two igniter clips short and blow the transistor in a shorted state. This is a good issue for KISS (Keep It Simple Stupid), since there are real safety issues.

    I've been monitoring this thread with interest. If I start having a kid around who is interested I would start flying birds again, but for myself only it isn't worth it. I do have a lot of good stories though, like the kid (not me) who couldn't wait for the glue to dry before he flew his Alpha. He managed to recover most of the pieces that fell off.
     
  6. SgtWookie

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    Bill,
    Somehow, you just triggered a couple of memories. I launched an Astron Streak with a big engine before it dried sufficiently; the fins ripped off and the rocket looped crazily around while everyone hit the deck. :eek: I never did THAT again.

    Launched an Astron Drifter with a 24" 'chute and a C6-4 engine on a windy day on a farm ... the rocket lived up to it's name and drifted very quickly out of sight, despite us chasing it in a Jeep. It seemed to be gaining altitude... :( Tried to stay away from 24" 'chutes and windy days after that....
     
  7. SgtWookie

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    It wasn't explicitly stated, but the only way it would be work-able is for multiple rockets launched in a sequential manner.

    I never used Centari products. My Dad started me off with Estes (after I blew up the kitchen trying to make rocket fuel :eek:) and decided to stick with them. Interesting, though.

    Many folks won't know what the heck we're talking about when we mention "flash bulbs" used in photography; as they've been replaced by now-inexpensive Xenon flashes for many years. One hasn't lived until they've juggled a hot flash bulb. :eek:

    That reminded me of another incident - flash bulbs were kind of inconvenient, as they were one-use items. Flash bulbs were somewhat similar to a "normal" lamp, except the glass envelope was chock full of an extremely fine tungsten filament, and the envelope was coated with a plastic-like material in case the glass shattered when the bulb went off (it frequently did).

    Kodak came out with the Instamatic; it used size 124 film that was in a nearly fool-proof to insert cartridge (just open up the back of the camera and drop it in), and it used "flash cubes":

    [​IMG]

    Advancing the film wind would rotate the flash cube to the next position for a total of 4 flashes before needing to replace it. Much more convenient than individual bulbs.

    But, on one deployment somewhere in the '77-'78 time frame, one of my fellow Marines went to get aboard a C-130 transport plane with a packet of flash cubes in one of the "cargo" pockets of his utility trousers; and there was enough RF energy present to ignite them! He wound up having to go to sickbay (emergency medical care) with 2nd degree burns on his leg.

    Absolutely. When pyrotechnic devices are involved, reliability and safety are very key issues.

    If you build them, they will come. :)

    Meanwhile, here's a pretty well-thought-out project:
    http://www.kevinshoemaker.com/projects/homemade-multiple-rocket-launch-system/
    10 igniter circuits with test, on/off lock, arm/safe lock, 1 set of wires per igniter.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    I found an old flash cube in a goodie box a while back and showed my kids what "state-of-the-art" used to look like, when the convenient little cubes replaced individual bulbs. (They get impatient waiting a couple seconds for their digital camera flashes to recharge, so the idea of having to pull a hot bulb and replace it for each shot was unimaginable to them.) We took a battery and popped a couple. Bright as ever. They were amazed. Remember that smell they used to make, from melting the safety plastic that surrounded the bulb? Mmmm... Plasticizers.

    And I'm another in the camp of those that have watched model rockets and even planes slip the surly bonds of...sight, as they recede into the distance.
     
  9. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    I'm going to spend some time on that link (kevinshowmaker.com) and look over those circuits. In the mean time...

    Scrap the radio controlled idea then. I would still like to incorporate the 4017, operated by a manual SPST switch from many feet away, to fire many rockets (one at a time) in sequence.

    I copied this circuit mostly from a 4017 ckt with LEDs operated in sequence by a pushbutton (SPST) switch. There was a pull down resistor with the switch to keep the clock pin of the 4017 from floating while the switch was open.

    *How do you correctly setup the reset pin for this situation?
    *Would I need an amplifying transistor with the BJT to increase the current fed to the base?
    -------
    I've read over that site, I plan to incorporate multiple safeties (I like the key switch idea) in the same manner.
     
    Last edited: Sep 3, 2011
  10. Wendy

    Moderator

    Mar 24, 2008
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    If you must use a transistor don't use a BJT. A MOSFET is easy to use and has excellent switching characteristics, much better that a BJT. I would plan on putting a fuse in line with it though

    For this one application I think a relay might work out better. If you have a shorted switch such as a transistor the safety key might save you, but you don't want the model launching unexpected like.

    My Dad apologized profusely when he straghted out the rudder of my second second Estes Falcon, a rocket that was loosely based between an airplane and a bottle rocket. Except for the engine tube it was all balsa, which is why I could rebuild the model with just balsa. Any how, the sucker only went up 50' but caught a thermal, and with the rudder straightened out the circles were much looser (which didn't spill as much air) and it rode the thermal clean over the mountain next to my dads 20 acres. We spent well over 30 minutes with binoculars watch it float out of sight, every loop 6" higher than last. It was almost worth it. I did get to provide a nice guilt trip on my Dad. Did I mention both of the these models I built were excellent gliders?
     
    Last edited: Sep 3, 2011
  11. SgtWookie

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    Jul 17, 2007
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    Are you familiar with the term "Switch bounce"?

    If not (or even if you are), you should spend at least a day reading through and understanding this material:
    http://www.ganssle.com/debouncing.htm
    .pdf format: http://www.eng.utah.edu/~cs5780/debouncing.pdf
    You should save the .pdf on your computer in case the website happens to be offline. It would save us helpers on here a LOT of time if everyone who ever used switches would read that material.

    Attempting to use a mechanical switch as a clock can result in big problems, as you will see as you read through Mr. Ganssle's thoughtful and rather thorough article.

    Another problem with using a 4017 as a sequencer is that you won't have an option to skip over a rocket if a last-minute problem is observed (such as a fin falling off or other unforeseen anomaly) and no provision to resume the sequence from a previously halted launch except for going through the entire sequence again.

    It's very important to not be hasty about slapping something together, then rushing out to launch a bunch of rockets. That's how accidents happen.

    It's an old cliche' but all too true: Safety is no accident.
     
  12. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    I planned for transistors because I've read of others using relays which wound up getting "welded" shut after a few launches. But I realize they were probably not using relays rated correctly for this application.

    Can a 4017 supply enough current to operate a relay for this setup or is an amplifying transistor needed also?

    *It's really only important that the 4017 remain in this setup so that I can operate one, single switch from a distance to launch multiple rockets, one at a time, in sequence.*

    Thanks for the advice so far
    --------------
    @ Sgt
    I'm in no rush at all with this project. Complexity wouldn't keep me from making this circuit operate with the idea of "sequenced, one at a time" launches.

    Yes, I'm familiar with denouncing the switch and will plan on doing this. (a 555 timer to send one pulse per several "bounced", unintended switch contacts per some unit time [dependent on the 555 setup]? ...Something along those lines.

    Surely, there's a way to correct the other problem you mentioned? "If a rocket is skipped" and coming back to it in the sequence. Even if it means de-arming the system and removing the rocket. It's not a big deal to me to have one not fire.
     
    Last edited: Sep 3, 2011
  13. Wendy

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    Mar 24, 2008
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    The relay welding is directly analogous to the transistor shorting, which is why I mentioned putting a fuse in line with the ignitor (a slow blow type, I can't recommend a current).

    As for switch bounce, it is an old problem, and many solutions have been developed over the years.

    Such as this...

    [​IMG]
     
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  14. wayneh

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    Why not just use a rotary switch? That would add the advantage of being able to see where you are in the sequence. And putting rotary switches in series would allow for as many spots as you could want.
     
  15. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    @wayneh
    That's a good idea & it would probably work fine, but my goal is to use the 4017 and a single switch to create the sequence. My objective isn't just to launch rockets, I also like the electronics side of it and would like to make the original idea work & learn from it. (Minus the radio controlled part).
    ------
    @Bill
    I'm reading Sgts link on de-bouncing and hardware/software ways to fix the problem. I don't really know how the circuit you linked works, but I figured it would be in the article since it's a fix.
     
  16. SgtWookie

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    Finally found what I was looking for:
    http://www.gwiz-partners.com/igniters.pdf
    See figure 11, on the 7th page. An Estes igniter when supplied 12v from a lead-acid battery will take ~12.4A for ~ 36.4mS.

    This article is specific to model rocket igniters, and is very well worth reading through to help understand what the current requirements are to light one of these engines. 12.4A is nothing to sneeze at, even if it is only for 1/27th of a second.

    I couldn't remember offhand what the igniter resistance was; I gave away the igniters I had some six months ago.

    So, 12.4A from 12.6v - that's close enough to 1 Ohm for me. That is a very good explanation for the reason of relay contacts getting welded. I'm sure a lot of those welded relays came from Radio Shack, and had contacts rated for 1A. Automotive relays would have been a much better (if more bulky) choice.
     
    Last edited: Sep 3, 2011
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  17. Rent2Own

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    Sep 2, 2011
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    Thanks for locating that. The current values and the article itself are a big help. I actually read through that the other day, though. From that page I knew the current would be high and that's why I thought I'd need resistors to protect the transistors. I'll pick relays that are rated for the situation and use fuses also.

    I'll pick an appropriate debouncing circuit for the switch and try and write up a new circuit to post. I'll use relays instead of transistors.
     
  18. SgtWookie

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    Even automotive relays have contact bounce. While they are rated for much higher current than a typical miniature relay, the contact bounce will cause burned contacts, constantly increasing the contact resistance, eventually resulting in failures; either insufficient current flow to heat the igniter or the relay contacts welded together. Still, it would likely take a large number of cycles for that to occur.
     
  19. Rent2Own

    Thread Starter New Member

    Sep 2, 2011
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    Ok. Well I'm going to take a few hours to sort through this information and i'll post a circuit/update tonight or tomorrow. Thanks for all the help.
     
  20. wayneh

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    Fair enough. I do like the idea of having a visual indicator of where the system thinks it is in the sequence. So I think I'd add an LED bank to show where your sequencer is, which line is hot. It will probably be very useful as you experiment and get farther along also - nothing beats being able to see what you're doing.

    My 2¢ on all the talk about relays is that I would probably look to use MOSFETs as my switches. They can take that big current surge and require little to drive their gate. Smaller, lighter, cheaper. Put a pulldown resistor on the gate to keep it low unless a valid fire signal is sent.
     
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