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- Oct 2, 2011
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New 4 PadLaunch Controller
Well after a year or more.. I finally finished my newcontroller. A while back while launchingmodels at a friend's ranch, I spent most of the time frustrated with thecontroller I had. The first one I builtyears ago was a dual pad controller modified from a MRC FX unit that wasdesigned to fire smoke engines for effect just prior to igniting the actualrocket motor on the model.
Here is whatit looked like in its original form from MRC.
I modified it a little, It had two sources for power,internal or external and for a couple reasons it was very intermittent. After the day was over I decided to build anew one that would be more powerful, reliable and of course less frustrating.
Here is a picture from that day......... Seemed like every launch took about attemptsto fire the igniters.
Well a couple years later and after much reading andresearch, especially on the Rocketry Forum; I have a new one ready for use.
I wouldlike to thank Steve Robb for his article about his 8 pad controller and a bigthank you for my friend Joe for his help, he is a wizard and a very knowledgeableelectrician. The plan was simple, Iwanted a 12V system, a pad box to provide ample power for fast response to thelaunch button. Also I wanted to be ableto test continuity at the Launch pad after connection, and again at the controls 50' or 200' away. Of course it had to have all the requiredfeatures of the NAR safety code and be asafe and reliable way to enjoy the launch. I used a yellow Pelican case to house the controls and a simple tool boxfor the pad box. The pad box houses a 12Amp Hour battery and the 6 relays to provide control and enable max current tothe igniters. I understand the danger ofa stuck or fused relay contact, so it has a provision for an alarm to indicatepad armed status. Also for this unit toaccidentally fire an igniter un-commanded would require both the pad arm andlaunch relays to fail at the same time.
The control box has Led status lights for Pad Power, ControlPower as well as a battery low indicator if the cell falls to a programmablevoltage; currently set at 9 VDC. The control switches are disabled if the keyswitch is off, there is also a mode select to test igniter continuity only orenable the pad arm switches. there arefour guarded Pad Arm switches to control each pad relay, as well as brightgreen LEDs to indicate igniter continuity that are designed to flash once theapplicable pad is armed. Finally alighted launch button. There areprovisions for a piezo buzzer to sound once a pad is armed.
The two small circuit cards at the bottom right of theunderside of the control panel in the left photo, are the flasher circuits forcontinuity/Arm.
The pad box contains the 12AH rechargeable battery and 6high amp (30A) relays. I also put highcurrent diodes at each of the 4 outputs to the common launch bus, to keep fromgetting false indications on an armed pad with no igniter during ignitertest. . The entire system is disabledsimply by flipping the switch on the front. It's not necessary but if one feels safer during rocket prep at the pad,turning the light switch off on the front will kill power to the entire circuituntil all models are prepped and you are 15 feet away from the pad. Then you can power the box and test igniter continuitybefore going back to the table for launch.
The back of the pad box has provisions for plugging in all 4igniter lead sets. Each lead is about 10-15feet long with traditional smooth copperalligator clips on each end. The redbuttons on top of the pad box are to test igniter continuity before leaving thepad area.
One of the best parts of this project was using the"Scheme It" program on Digikeys web site.
( https://www.digikey.com/schemeit ) I have a few nice schematics of the wholething drawn out using their software, turned out pretty cool.
All ofthe LEDs on the control box and the pad box are all very bright, and are much easierto see in the sun then the lights in any other controller I have used before. I may end up switching the circuit breakerout for a higher one as the one I had is only 20 amp, which I am sure will befine but let's say I got four models ready to go with clusters in each one andI want to launch them at the same time. Estes Solar igniters can pull over 2 amps apiece for a second or twowhen lit up. The set up allows me tolaunch one model at a time or all four models at once if I wanted to drag raceor something. Another feature I had tohave was the ability to use any igniters without worry about premature ignitionduring test. Q2G2 igniters have an allfire rating at only 150 Milliamps, and most of you know many have beeninadvertently fired using other launch controllers because the test circuit woulddraw to many amps.
Feb16th 2016, I just finished another full functional check of the controller andpad box. Even tested the circuit breakerwith a direct short test. The pad box isprotected with a 20 Amp circuit breaker that; with a set clips shorted at the pad, trips after about 12 secondsof holding the launch button. The wirewhip from the box to the pad warms slightly, the clips got pretty warm andthere is no damage to any other wiring or circuitry. Each pad arm relay, the master arm relay and the launch relay are all rated at 30 amps,so they will handle the job well.