chapter 14

CHAPTER 14

MAKING THE IGNITION CONTROLLER

The ignition controller is a remote control device that provides thevoltage necessary to start the rocket engine. It allows the rocketto be launched from a safe distance with minimal equipment.

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Purchase the following parts:• Two 9 volt snap in battery holders.• One N-cell battery holder.• One N-cell 12 volt battery.

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Two 9 volt snap in battery holders.One N-cell battery holder.One N-cell 12 volt battery.

www.mcmaster.com part number 7712K62.www.mcmaster.com part number 7712K91.www.mcmaster.com part number 7735K23.

Purchase the following parts:• One roll stranded single conductor wire.• One 6’ length of continuous flex multi-conduc-tor cable.• One pair fully insulated alligator clips.

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One roll stranded single conductor wire.One 6’ length of continuous flex multi-conductor cable.One pair fully insulated alligator clips.

Really any type of wire can be used to connect the alligator clips to theignition controller as long as it’s capable of carrying enough amperagefrom the ignition controller to the rocket engine igniter.

www.mcmaster.com part number 7587K325.www.mcmaster.com part number 7673K57.www.radioshack.com part number 270-354.


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Purchase the following part:• 6” x 6” x 4” Plastic junction box.

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6” x 6” x 4” Plastic junction box.

www.homedepot.com part number 499-979.

The plastic junction box will be used to house all the electronic compo-nents for the ignition controller. A foam seal between the box and the lidof the box keeps dirt and debris out.

Purchase the following parts:• One liquid tight cord grip.• One SPST heavy duty rocker switch.

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One liquid tight cord grip.One single pole single throw heavy duty rocker switch.

The liquid tight cord grip will keep dirt and debris out of the ignition con-troller as well as prevent the cord from being pulled out of the box.

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www.mcmaster.com part number 69915K61.www.radioshack.com part number 275-690.

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Purchase the following part:• One wireless 2 channel momentary relay mod-ule.

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One wireless 2 channel momentary relay module.

Search ebay.com for a wireless 2 channel momentary relay module.They usually cost between $20 to $30.

Remove the four screws holding the lid to the topof the junction box. Set the lid and screws asidefor now.

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Using a 7/8” spade bit, drill a hole on the side ofthe junction box. Drill the hole on any side of thejunction box about half way down the box andover to one side. See picture for clarification.

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Remove the plastic nut on the liquid tight cordgrip and install it in the 7/8” hole on the side ofthe junction box. Tighten the platic nut to theback of the cord grip so that it’s secure.

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The 6’ wire that connects the ignition controller to the rocket engine willgo through this cord grip.

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A spade bit is used for fast drilling of holes in wood and plastic. Spadebits have a forged, flat paddle with a guide point and cutting edges oneither side.

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Using a 5/8” spade bit, drill a hole on the side ofthe junction box next to the cord grip. Drill thehole on the same side of the junction box as thecord grip, about half way down the side of thebox.

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Remove the plastic nut from the back of therocker switch. Put the switch in the 5/8” hole tomake sure it fits correctly. Remove the switch andput it aside for now.

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There are some wires that need to be soldered to the back of the switchbefore it can be installed on the side of the box.


A spade bit is used for fast drilling of holes in wood and plastic. Spadebits have a forged, flat paddle with a guide point and cutting edges oneither side.

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Remove the plastic insulating jackets from bothalligator clips.

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The plastic insulating jackets need to be removed so two wires can besoldered to the alligator clips.

Remove 6” of insulation from one end of the con-tinuous flex cable.

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CHAPTER 14

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Cut wire number 3 and the green wire with theyellow stripe off at the base of the insulation.

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Only two wires are needed to connect the ignition controller to therocket engine igniter.

The wires in the continuous flex cable are marked 1, 2 and 3 along witha green wire with a yellow stripe.

Purchase the following part:• Heat shrink tubing 1/8” to 1/16”.

Cut a 2” length of 1/8” heat shrink tubing. Installand shrink the tubing on the two remaining wires.

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Heat shrink tubing 1/8” to 1/16”.

Electrical tape can be used in place of heat shrink tubing.

www.mcmaster.com part number 7856K631.


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Purchase the following part:• Heat shrink tubing 1/4” to 1/8”.

Cut a 2” length of 1/4” heat shrink tubing. Installand shrink the tubing over the cable insulation aswell as the two wires.

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Heat shrink tubing 1/4” to 1/8”.

Electrical tape can be used in place of heat shrink tubing.

www.mcmaster.com part number 7496K435.

Strip 1/2” insulation from the end of each wire.

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CHAPTER 14

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Put the two insulation jackets from the alligatorclips on the two wires.

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Once the alligator clips are soldered in place, it won’t be possible to putthe insulation jackets over them.

Solder the two alligator clips to the two wires.

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Solder with rosin flux core.

Many articles and tutorials on basic soldering techniques are availableonline. Search Google, YouTube and Wikipedia.


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Slip the insulation jackets back on the alligatorclips

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The insulation covers on the alligator clips will prevent the two clips fromtouching and accidentally shorting the ignition controller.

Put two small pieces of 1/2” wide double sticktape on the back of each 9 volt battery holder.

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3M Very high bond double sided tape 1/2” width or similar.

Silicone adhesive would be a good alternative to double sided tape.

www.mcmaster.com part number 75935A11.

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Cut a 2” length of 22 gauge stranded wire. Strip1/2” insulation from both ends of the wire.

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This wire will be used to connect a positive terminal on one 9 volt batteryholder with a negative terminal on the other 9 volt battery holder. Put-ting the two batteries in series like this will produce 18 volts.

Solder one end of the wire to the negative termi-nal on one of the battery holders. Then the otherend of the wire to the positive terminal on theother battery holder.

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This wire will be used to connect a positive terminal on one 9 volt batteryholder with a negative terminal on the other 9 volt battery holder. Put-ting the two batteries in series like this will produce 18 volts.


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Put the free end of the continuous flex cablethrough the cord grip on the side of the junctionbox. Pull enough cord through so you have roomto work.

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Do not tighten the cord grip yet, that will be done in a later step.

Remove 6” of insulation from the end of the con-tinuous flex cable. Cut wire number 3 and thegreen wire with the yellow stripe off at the base ofthe insulation.

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Make sure you cut the same wires as you did in step #13.

CHAPTER 14

Only two wires are needed to connect the ignition controller to therocket engine igniter.


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Solder wire #1 to the remaining positive terminalon the 9 volt battery holders.

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Cut a 6” length of 22 gauge wire. Strip 1/2” insula-tion from both ends of the wire.

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Solder the 6” length of 22 gauge wire to the re-maining negative terminal on the 9 volt batteryholders.

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Place the wireless relay module inside the junc-tion box directly behind the cord whip.

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The wireless relay module is held in place by two small sheet metalscrews. Placing the module in the box will help to determine where thescrews will go.

CHAPTER 14



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There are two holes on the relay module boardfor mounting screws. Using a black Sharpiemarker, mark two spots on the junction boxwhere the screws that will hold the relay modulewill go.

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Black Sharpie marker or similar permanent marker.

Put the relay module aside and drill both holes inthe junction box with a 1/16” drill bit.

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Using a small flat screwdriver, secure the wirefrom the negative terminal of the battery holderto the terminal block on the relay modulemarked NO1.

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NO1 stands for normally open terminal #1.

Using a small flat screwdriver, secure the wiremarked 2 from the continuous flex cable to theterminal block on the relay module markedCOM.

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COM stands for common.

CHAPTER 14

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Cut a 6” length of 22 gauge wire. Strip 1/2” insula-tion from both ends of the wire.

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Solder the 6” length of 22 gauge wire to eitherterminal on the rocker switch.

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This switch will power the relay module on and off.

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Put the 22 gauge wire and the rocker switchthrough the 5/8” hole on the side of the junctionbox. Attach the plastic nut that came with therocker switch to the back of the switch. Tightenthe lock-nut until the switch is securely in place.

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CHAPTER 14


Put a small pieces of 1/2” wide double stick tapeon the back of the 12 volt battery holder.

3M Very high bond double sided tape 1/2” width or similar.

Silicone adhesive would be a good alternative to double sided tape.


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Using a small flat screwdriver, secure the blackwire on the 12 volt battery holder to the terminalblock on the relay module marked GND.

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This small 12 volt N cell battery will power up the relay module.

GND stands for ground.

Solder the red wire from the 12 volt battery holderto the remaining terminal on the back of therocker switch.

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Using a small flat screwdriver, secure the 22gauge wire from the rocker switch to the terminalblock on the relay module marked VCC.

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VCC stands for grounded voltage of the collector/emitter/base. For ourpurpose, it means the positive terminal of the 12 volt battery.

Carefully attach the relay module to the bottomof the junction box with two #6 x 3/8” Sheetmetal screws.

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#6 x 3/8” Sheet metal screws.

Silicone adhesive or double stick tape could be used in place of sheetmetal screws.


CHAPTER 14

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Carefully push the antenna from the relay mod-ule through the cord whip so that it’s sticking outthe end of the cord whip a few inches.Tighten the cord whip with an adjustable wrenchuntil the flex cable and antenna are secure.

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The cord whip will prevent the flex cable and antenna from being pulledout of the junction box.

The antenna on the relay module is a small black wire about 6 inches inlength. The length of the antenna is critical to the proper operation ofthe relay module. Do NOT trim it or adjust it.

The components of the ignition controller and thewiring should now look like this.

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Install two 9 volt batteries and one 12 volt batteryinto the battery holders in the ignition controller.

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Two 9 volt batteries.One 12 volt battery.

Hook up the two alligator clips from the ignitioncontroller to the test probes on a digital multime-ter.

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A small light bulb can be used in place of the multimeter.

CHAPTER 14

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Turn the switch on the side of the ignitron con-troller to the on position.

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The switch on the side of the ignitron controller isolates the relay modulewhen the ignition controller is not in use. This extends the life of the 12volt battery.

Press button A on the remote control and themultimeter should read 18 volts. Release button A on the remote control and themultimeter should read 0 volts.Put the cover on the top of the ignitron controllerand secure it with the four screws that came withit. The ignition controller is now ready for use.

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chapter 14

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