Building a Cluster Model Rocket Luncher

Discussion in 'The Projects Forum' started by Tallonejosh, Dec 1, 2009.

  1. Tallonejosh

    Thread Starter New Member

    Dec 1, 2009
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    Hello i am making a rocket in my physics class that has a cluster of 7 engines. These are going to be at the largest C6-5 engines. I am going to need a device that ignites these engines at the same exact time. I was wondering if anyone would know of an inexpensive way to do this that a couple of high school students could accomplish.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    What are the ignition requirements (voltage, current)?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Do you realize that three D-series engines will be nearly the same power as seven C-series engines? And that since the resulting assembly will likely be lighter than seven C-series engines, you'll have higher equivalent thrust?

    To ignite seven C6-5 engines simultaneously will require quite a bit of current. You'll have to use a 12v system powered by a lead-acid battery.

    Estes igniters have a resistance of about 1 Ohm. With a 12v system, that means 12 Amperes per igniter, or a total of 84 Amperes for about 30mS.

    This PDF has data on various rocket igniters: http://www.gwiz-partners.com/igniters.pdf
    Estes igniters are on the 7th page.

    You might get them ignited using less voltage/power, but the likelihood of simultaneous ignition declines steeply.

    You will probably need the power source located close to the launcher to minimize the voltage drop across wiring, or you would need very heavy-gauge wire; the latter would be expensive.

    Igniting three D-series engines would require less than half that amount of power; 36A for 30mS.

    These are just some initial considerations.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    If you're really bent on using seven C6-5 engines, here is one way you could connect them:

    [​IMG]

    You won't have individual igniter continuity check, so you will need to be quite careful to ensure they are in fact connected to the copper "rings".
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Sgt's configuration will work just fine, been there- done that; 1949, fired 9 skyrockets same way with car battery- prob. 6V then, used short Ni-Cr wire loops for igniters, all fired.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    This goes with that other thread about a model rocket launcher. There is enough money in engines I think it would be worth building a scanning continuity tester.

    But for starters, I would use some grabber clips similar to these. They will get damaged during launch, but they would hold on to the igniter leads much better, and would be much less likely to short out to another set of leads.

    [​IMG]

    Radio shack carries these, but they are much cheaper elsewhere.

    http://www.radioshack.com/product/index.jsp?productId=2062232

    The scanning continuity tester is a different issue, but within the realm of a high school electronics class to make. Far as I know it has never been designed by anyone.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Ugh - sad to say, those particular Radio Shack clips are terrible nowadays. :(

    They used to be pretty good, but now they just fall apart.

    Many years ago, I used solid copper miniature alligator clips that worked very well. I have no clue if you can even get them anymore; nowadays they're all nickel plated steel.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    I used to use the clips too, but I blame them for most of my cluster failures. You need something that will grab and hold, securely. I didn't have the access to parts or the money to buy them back then.

    Radio Shack isn't the only source, matter of fast much smaller models of clips are available elsewhere for much less. I used that by way of example.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Many years ago, I used the heavy-gauge copper ring trick with multi-engine launches; it worked well as long as you were careful to clean any tarnish off the copper, and wrap a whole bunch of turns of the Nichrome igniter ends around it. My crude drawing was just a rough illustration of the concept.

    It can get really hairy if you're trying to connect a bunch of igniters.
     
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