Estes Launch Controller Modifications

Note: this information was taken from Programming Pete's Web Page. It can be seen at: http://www.tfs.net/~petek/projects.html

Estes Launch Controller Modifications

At some point of time you may want to use your Estes Launch controller with something other than a standard Estes igniter. Perhaps you've made up an igniter from one of the igniter kits available from folks on the web. Or maybe you've been experimenting with electric matches or flashbulbs (please don't use flashbulbs!). In any event, you might find that the Estes Launch controller fires off your igniter just as soon as you insert the safety key and well before you press the launch button! OUCH!

The problem with using the Estes Launch controller for anything other than Estes igniter's is that the Estes launch controller uses a design that is perhaps 30+ years old. Not a bad design mind you, it's actually a great design; a simple design. Follow me on the schematic (and use your imagination a little bit as I don't show the igniter's in the schematics... just imagine the clips as shorted together through an igniter).

The battery (4 AA cells, six volts) current is passed through a lamp. The current then goes out to the igniter and back to the negative side of the battery (we're using conventional current flow here, not electron flow). If the igniter has continuity the current path is unbroken and the lamp illuminates. As it happens, the resistance of a hot filament is pretty high; high enough that the resistance limits the amount of current flowing in the circuit. The limited amount of current is low enough that the igniter will not ignite. Pressing the launch button shorts out the lamp, dramatically increasing the current flow and causing the igniter to burn. Whoosh, up goes your rocket.

The limited amount of current flowing in the circuit when the lamp is illuminated is fine for Estes igniter's. But other igniter's may actually fire on the limited current. I measured my Estes launch controller's current... 180 mA. Put another way, 0.180 amps. Doesn't sound like much if you are familiar with electronics... electronics that are 30 years old :-)

Today's electronics -- and many igniter's -- do just fine with 180 mA. There are electric matches available that will fire without hesitation at 180 mA. Flashbulbs will probably fire at 180 mA. Like I said, nice design, simple design -- but an old design.

What we've got to do is decrease the current -- and decrease it a lot. Since the lamp is the cause of the problem, we'll just replace the lamp with a low current device -- a Light Emitting Diode (LED). Take a look at the new schematic. Notice that the lamp is replaced by a LED and a current limiting resistor. In the prototype I used a 4000 mcd, yellow LED. The current in the circuit while measuring continuity was measured to be 8.4 mA. Quite a decrease!

Building the modification is actually quite easy. You start by removing the lamp from the controller and breaking the lamp! Remove the lamp and wrap it in some heavy paper (a few layers of newspaper will work). Using a pliers, squeeze the glass bulb until the bulb breaks. USE CARE! You want to break the glass bulb without distorting the metal part of the lamp. The glass bulb is quite thin and will break into lots of sharp tiny pieces of glass. Be very careful to not cut yourself on the broken glass.

Using a pair of needle nose pliers (and great care) remove all of the tiny pieces of glass that may still be sticking to the metal (base) part of the lamp. Use a soldering iron to melt and remove the solder ball at the bottom of the base and from the side of the base. Remove the filament stem from the base. Clean out any remaining glass or other garbage.

Prepare an LED and resistor by clipping the anode lead of the LED so that the lead is about 1/8" long. The anode lead of the LED is the one that is opposite of the flat on the base of the LED. Clip one lead of the resistor to 1/8" long. Tin both the LED anode lead and the shortened resistor lead. Solder the LED anode lead and the shortened resistor lead together by holding the two tinned leads in contact and heating with a soldering iron to reflow the solder.

Bend the cathode lead on the LED perpendicular to the LED. Insert the prepared LED/resistor pair into the lamp base so that the long resistor lead comes out the bottom of the lamp base. Jiggle everything around to center the LED in the lamp base. Solder the long resistor lead to the bottom of the base, using extra solder to create a solder ball. Clip off the excess resistor lead length. Solder the cathode lead from the LED to the side of the lamp base (at the same spot where you unsoldered the filament earlier).

Secure the LED to the lamp base with some hot-melt glue. You might want to ohm out the LED-lamp to make sure everything is ok.

Insert the LED-lamp into Estes Launch controller. Put the safety key into it's hole. Short out the igniter clips. The LED will illuminate.... and draw a LOT less current.

Finally... what about the Quest controller? Well it just so happens that I couldn't resist buying a Quest controller (and rocket). I just *had* to have one of those Quest flying saucers ... and the pistol trigger style controller looked pretty neat. Anyway... it looks like Quest has got the right idea when it comes to launch controllers. The Quest controller seems to use an LED already (I didn't take the controller apart to check). The Quest controller also has a beeper that sounds when the safety key is inserted and continuity in the igniter is verified. Total current draw in the circuit? 13 mA. Pretty darn good.