Introduction: How to Build a Model Rocket Launch Controller With a Removable Key

These instructions will guide you through building a model rocket launch controller with a removable key for use with standard Estes rocket igniters. Building a launch controller with a removable key allows you to completely disable the launcher before approaching the launchpad which decreases the chances of an accident while readying a rocket. This procedure will require soldering ability for connecting various electronic components. Also required is knowledge on how to operate a drill press. From setup the procedure should take around two hours to complete, and then you will have a fully functioning launch controller, ideal for use with Estes model rockets.

Step 1: Gather Materials and Tools.


  1. Plastic Pencil Case or Index Card Box
  2. 2 Binding Posts
  3. RCA Plug
  4. Disassemblable RCA Jack (Often indicated by a small removable ring at the base)
  5. Small Momentary Push-Button Switch
  6. 25 Feet of 2 Conductor Speaker Wire
  7. Lamp Bulb That Will Operate Between 4.5 and 6 Volts. Warning - Under no circumstances exceed a 6 volt capacity. This may allow ignition without a button press.
  8. Lamp Holder of the Same Size as the Bulb
  9. 2 Alligator Clips
  10. 4 AA Battery Holder and batteries


  1. Wire Cutters
  2. Sharpie
  3. Soldering Kit
  4. Drill Press
  5. Any additional tools required to mount the materials (may require a screwdriver, wrench, or pliars)

Warning - All tools have their own safety regulations which should be used to avoid injury. Ensure that you understand the usage and safety procedures of any soldering iron, drill press, or other tool before attempting to use them.

Step 2: Use the Sharpie to Mark the Spots on the Box Where You Want to Place the Button, the RCA Jack, the Binding Posts, and the Lamp Holder.


  • The binding posts should be placed close to a back or side edge, as they will have long trailing wires connected to them.
  • Avoid placing components within an inch of each-other or on non-flat portions of the box. Doing this may complicate creating the mounting holes.
  • If your chosen box is shallow, remember that a battery pack will be placed inside of it and adjust spacing accordingly.

Step 3: Use the Drill Press to Create the Holes in the Lid.

  • Each part should list on the packaging what size of hole it can be mounted in.
  • If possible, Open the lid of the box and place a scrap of wood under it as a base before drilling. This will make producing clean holes easier.
  • Drill slowly so as not to fracture the plastic.

Step 4: Mount the RCA Jack, Button, Binding Posts, and Lamp Socket.

Mount all components securely except for the lamp holder; this component will be removed again in a couple of steps.

Step 5: Cut and Strip the Wires.

For your launcher you will need wires that go

  1. From the positive (red) binding post to the positive (red wire) end of the batter pack.
  2. From the negative (black wire) end of the battery pack to the RCA jack.
  3. From the other connector on the RCA jack to the lamp holder.
  4. From the same connector on the lamp holder to the button.
  5. From the other connector on the button to the unused lamp holder connector.
  6. From the same lamp holder connector to the unused binding post.

Use the wire cutters to cut single-strand wires from the double-strand speaker wire that reach these distances then strip them to expose the copper.


  • Leave a bit of slack in the wires when measuring.
  • Avoid striping any more than a centimeter of wire. Even that is a bit more than you need, and the more exposed wire you have the easier it is to cause a short.
  • The rest of the wire will be used to connect the controller to the rocket. To that end, try to keep the two sides of the wire somewhat even.

Step 6: Remove the Lamp Holder and Solder Its Wires.

Since the lamp holder has the most wires connected to it, it is generally a good idea to remove it before soldering the wires on.

Caution - At this and any other time you solder with this project, be careful to avoid any plastic with both the soldering iron and the actual solder as the plastic can easily melt.


  • Depending on the shape of your holder, it may be necessary to have it held up by a vice or clamp.

Step 7: Securely Mount the Lamp Holder.

Now that the lamp holder has all wires attached, it can be permanently mounted to the box.

  1. Thread all wires through the lamp holder's hole.
  2. Place the holder securely on top of the hole.
  3. Use whatever tools necessary (in the example case a screwdriver) to tighten it down.

Step 8: Solder the Other Cut Wires Into Place.

None of the other components will be removed from the box before soldering. Use the wires cut in step five and solder them into place.


  • Some components, such as the binding posts, may separate into multiple pieces. Removing the portion you are trying to attach solder to and folding it in a clamp reduces the chance of accidentally melting plastic.

Step 9: Install the Lamp Bulb in the Lamp Holder.

Step 10: Cut Even and Strip the Ends of the Remaining Speaker Wire.

All of the wire you have leftover will become the wire that runs from the controller to the rocket. You should still have well over 20 feet remaining.

Step 11: Disassemble the RCA Plug

In order to make the plug function as a key, a wire must be added to its internal components. If your plug is similar to the example plug, then the following may work:

  1. Gently pry away the plastic ring at the base.
  2. Open the plastic housing just far enough to remove the metal component.
  3. Remove the metal component and set the plastic housing someplace you'll be able to find it.

Step 12: Solder a Wire Scrap Onto the Plug.

By this point there's a good chance you have a small scrap of wire from cutting and trimming the speaker wire. If you don't, cut one now. You only need a piece long enough to reach from one metal part of the plug the the other.

  1. Strip your wire fragment completely.
  2. Solder it into place between the two metal portions of the plug.

Warning - This solder carries an increased risk of coming in contact with plastic. Take extra care not to melt a portion of the plug.

Step 13: Reassemble the Plug.

To get the plug back in its casing, simply reverse the steps taken to get it out.

  1. Place the metal component in the plastic housing.
  2. Close the plastic housing.
  3. Use the ring to hold the plastic housing shut.

Step 14: Attach the Two Alligator Clips to One Pair of Ends on the Stripped Speaker Wire.


  • Based on what type of alligator clips you have this may be done with a screwdriver, or you may need to solder the wire to the clips. Either way solder will be more secure.

Step 15: Attach the Other Ends of the Speaker Wire to the Tops of the Binding Posts.

Step 16: Insert Batteries Into the Holder.

Your launch controller is now complete. If you remove the RCA plug and keep the alligator clips separated the lamp should remain off until you insert the RCA plug AND clip the alligator clips to each-other. While the lamp is lit, pushing the button should cause the lamp to turn off. If it passes these tests, then you controller is ready for countdown.


  • If the bulb does not light at all, try tightening the binding posts and re-inserting the bulb. These are the simplest problem to fix as they are the portions that are not soldered down.
  • If the bulb flashes and then won't turn on again, then you may have a bulb with too low of a voltage.
  • If the bulb lights in ANY other situation than the one described above, then there is most likely a problem with your wiring such as a short or misplaced wire.

Step 17: Usage

Using the key-operated launch controller is similar to standard Estes launch controllers. When using the launch controller have whoever approaches the rocket remove the plug and keep it in their pocket anytime they approach the rocket. Connect one alligator clip to each end of the igniter. Once back at the controller and a safe distance away insert the jack. If the lamp lights up, you are clear for launch. Hold the button down for two seconds to ignite the engine.

Warning - If the lamp lights but the engine does not ignite when the button is pressed, wait at least two minutes before approaching the rocket with caution. This may be caused by a faulty igniter or engine and the rocket should be considered active until the engine and igniter can be removed and evaluated.