How To Build A Simple Cluster Igniter

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Design
One of the biggest reasons for cluster rockets remaining unpopular is the amperage needed to simultaneously ignite the motors. 2 amps per igniter is needed. Your basic commercial igniter cannot deliver this amperage. After checking out what was available on the market that could deliver this amperage, I decided to try to build a SIMPLE lightweight igniter that would deliver at least 12 amps, I didn't envision building any airframes with a larger cluster than five which would require 10 amps, so 12 amps would give me 2 amps to spare as a target.

My design consists of 2 110 AC vacuum cleaner cords, a SPST switch, a handful of male/female 110 AC plugs and an aluminum enclosure to house the switch. Its power supply is a 12V car battery. My Crown Vics battery puts out 950 CCAs, so I am just limited by cable resistance on 35' + of cable. Vacuum cleaners use an enormous amount of juice and their cables are rated at 16 amps, so I know it could handle the amperage I needed. I knew those old cables I cut off discarded vacuums would come in handy someday!

This design consists of a pair of car battery clamps that lead to the launch switch, which leads to 18' of cable with microclip igniter leads on the far end. This is sufficient for motors up to C size. A second 18' extension can be added to get the length of cable out to 38' +, including the car battery leads, to give you the space needed for motors larger than C.

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I had a 7.2V 3600 mAh R/C boat battery that I also included in the pictures as an alternative power supply. This battery puts out enough juice to launch a single motor, but not clusters. Ni-Cad R/C batteries are light enough to carry around but cant be relied upon to put out the amps needed for cluster work. A better choice for single motor launches would be a 12V Ni-Cad R/C battery, but the largest I had on hand is a 7.2V.

Build
The build consisted of raiding my household junk box for:

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• 1 SPST switch 12V, 20 amp rated
• 2 18' 16gauge vacuum cleaner power cables
• 4 microclips
• aluminum enclosure
• 2 110 AC female polarized plugs
• 3 110 AC male polarized plugs
• 2 car battery clamps

The parts were soldered according to the schematic.

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I also soldered up 6 “clip whips.” These are igniter extensions that split from 1 microclip into 2, 3, 4 or more microclips needed for igniting multiple motors. I made 3 of each; single clip to 2 clips and single clip to 3 clips. This is all I need for up to 5 clusters because, I wire up the motor igniters to each other. I can launch 3 motors easily with a standard 2 microclip igniter using this method. The biggest problem here is motor hooks getting in your way.

Performance
I tested the igniter by igniting 4 18mm and a single 24mm motor placed in a dirt hole with nozzles facing up. I used my second extension for a total of 38+ feet of cable. With the vehicle shut off, this igniter setup ignited all 5 motors simultaneously with no problem, delay or blip. I continued to make 14 other launches, including a 3 cluster with no hint of a problem or need to turn the car on to re-power up the battery.

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The only drawback to this cluster igniter is that you must get within 38' of the launch pad with a vehicle. This is usually not a problem for me, but you could carry a smaller motorcycle battery to overcome this drawback.

GUEST's OPINION:
"" (X.X.)

1. General
   A digital multimeter is invaluable in tracking down problems in launch controllers. Bad solder joints, high resistance in switches and even checking the available voltage/amperage from the battery is very easy with a digital meter. I recently converted my power source from small 9 volt batteries (which struggled to supply 2 amps) to NIMH AA batteries, which were capable of around 5 amps with the launch controller. This means a much faster response when launching single engine rockets, and more reliability for 2 and 3 engine clusters, while keeping the whole launcher light and compact. - S.T. (Australia)
2. Igniters
   With clusters, I always scrape the oxidation, place the igniter, add some black power (1-2 cubic mm) and then tamp with wadding. The wadding must be pushed deep into the fuel area to hold the powder in. In 35 yrs, I've never had a cluster ignition failure using this method. The small amount of black powder gives the pyrogen an unbeatable boost. The powder is from a sacrificed engine (a 1/4A will do for years) and is powderized with a morter and pestle. I tested a small pinch first, grinding and giving it a good smack with the pestle, and couldn't get the expected small pop. – J.L.
3. Igniters
   Cluster ignition - One more important tip: check the continuity of each igniter AFTER plug installation but BEFORE you twist them all together. But this test won't tell you if your Estes igniter is shorted upstream of the pyrogen tip. If one of the igniters is pre-shorted, you'll never get that particular motor lit. This is all the more reason to go with thin (such as 30 AWG kynar wire) Igniterman or Magnalite igniters to light BP motors. - B.K. and C.P. from RMR