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To build, or to buy a LPR/MPR Launch Controller?

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TangoJuliet

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Howdy Y'all! I haven't flown model rockets in almost 30 years and Holy Cow! a lot has changed! In my pre-teens and teens I competed in NAR sanctioned events with the Summit City Aerospace Modelers (SCAM) in Ft. Wayne, IN, where I grew up, until I joined the USAF in 1989 and could afford R/C airplanes - which I still enjoy. Anywho... I recently found myself reminiscing about my rocket days while watching some YouTube videos. I decided I wanted to re-live some of that fun, and pulled the trigger on a North Coast Rocketry Laserhawk kit from Apogee Rockets.

After all these years away, I need to replenish my Ground Support Equipment. I could easily purchase a launch controller that would handle LPR/MPR, but I'm wondering if I could make one for less? What I'd like to have is one that uses a 12V Gel-cell (that I already own for my R/C field box), and perhaps have the expandability to launch 3 rockets at once (ala "Drag Race") if I were to use it in conjunction with some of the local school programs.


My biggest challenge to attempting this is that I'm electronically ignorant! :( Simply... I've never had a course in electronics. I haven't even used a multimeter in over 20 years! I can solder two wires together with good results, but I can't read a wiring diagram, and I don't have the comprehension required to understand the requisite components necessary to create what I want/need.


I'm kind of hoping someone here has already done this a time or two and can provide me with a Bill of Materials and a "Diagram For Dummies" that I could follow to build my own. Assembling all the parts doesn't appear too difficult to me, but knowing what parts to get, and how to properly create the circuit with the required "Safety" measures is beyond me.
 

GregGleason

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Welcome!

Many of us followed a similar path (I preceded you into the USAF by 10 years) and want to have fun again.

To answer your question, the answer is "Yes" for a simple but effective system.

Here are some launch controller schematics that I have collected. You can try whatever level you are comfortable with. Just keep the main thing the main thing.

Centuri.Schematic.71dcen72.jpg

View attachment 295155

Launch Controller Schematic SPDT.jpg
Have fun!

Greg
 

TangoJuliet

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Thanks Greg. The middle diagram appears to be what I'm looking for. I think I read, while searching, that LED's with resistors can be a little tricky. I think there's a specific polarity requirement when using them. The last one is a little more confusing, but essentially the same I guess.
 

GregGleason

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You are welcome.

The important thing is that you have fun while you learn. Most of us (like me) are in the same boat as you regarding their understanding of electronics, but there are some very knowledgeable people on this forum who know quite a bit the topic of electronics, so if you have a specific question then post away.

Also, there are likely a lot of YouTube videos on the LED's or other "how to's" on the interwebs that might be helpful.

Greg
 

sghioto

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The last diagram was a custom design with a few extra features that were requested, but correct does the same thing. LEDs are polarized and safe, just reverse the connections if it doesn't work, shouldn't damage anything.:)

Steve G
 

TangoJuliet

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Thanks guys. Any recommendations on gauge of wire for components and for leads to the launch pad? I kind of like the idea of using a bayonet plug for my launch leads to the controller, so that it is easily disassembled for storage/transport.
 

sghioto

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16 gauge should be good to at least 50 feet for igniter cables. 18 gauge should be fine for the internal wiring on the controller. Use a 470 ohm 1/2 watt resistor in series with the red LED.

Steve G
 
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TangoJuliet

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Thanks sghioto! You must be an electrical engineer, I saw quite a few posts from you during my initial query through the forums.
 

TangoJuliet

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Thanks sghioto! You must be an electrical engineer, I saw quite a few posts from you during my initial query through the forums.

I was reading a research paper by J.R. Brohm (NAR #78048) titled "Igniter Continuity Tests" where he scientifically tested four different brands of igniters to determine the lowest voltage needed to fire the igniters in order to hence determine the safest low voltage necessary to obtain a continuity test circuit without accidental firing of the igniter. Pages 18 and 19 have diagrams for an LED Continuity Check Indicator, and a Transistorized Continuity Check Circuit. The diagram for the LED Continuity Check Indicator is exactly as simple as the old Estes Electron Beam Launch Controller - no frills - and it's what I'm looking for, but... A few frills would be kind of nice. When the safety key is inserted, the continuity lamp receives power (if continuity exists), then depressing the Launch button allows full voltage to the igniter for engine ignition. Is it possible to include an LED on the safety key to indicate power to the controller, prior to the continuity check LED? How would that be wired into the circuit? How would I add provisions for 2nd and 3rd individually controlled igniters (separate rockets)?
 

TangoJuliet

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You da man! :headbang: Thank you very much!

In that diagram, what is the purpose of the diodes (since I don't know what diodes do)? I'm assuming D1-3 are diodes. And I would still need resistors on each of the LED's, correct?
 
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sghioto

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Diodes are components that allow current to flow in only one direction. The diodes provide isolation for the igniter continuity LEDs. The LEDs shown in the schematic are the 12 volt type with the built in resistor otherwise install a 470 ohm 1/2 watt series resistor.

Steve G
 

TangoJuliet

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Gotcha :wink:.

Ok, one more silly question... Where is the best place on-line to purchase all of these components, including a project box to build it on?
 

sghioto

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BEC

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Proper attribution of the diagram in post 5: http://xkcd.com/730/

To return to topic..... our local GSE-meister uses a design that allows one to check continuity (and select the pad you want to use) without actually arming the panel. I will see if I can find the schematic and add it here.
 
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sghioto

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a design that allows one to check continuity (and select the pad you want to use) without actually arming the panel
This modified version will accomplish that if needed.

Steve G

Launch controller 3 pad #2.jpg
 
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