View Full Version : Scratchbuilt Launch Controller.
1st June 2010, 04:07 PM
When I first entered the amateur aerospace hobby thirty years ago my first launch controller was an orange Estes with only 15 feet between myself and the rocket. I never thought of any risks associated with such close proximity of a launching rocket and myself. This arrangement worked quite nicely for my first ten years in rocketry. After a 20 year hiatus from rocketry my oldest son (Rocketeer41) got me back into rocketry. Most of my old equipment was still in my bedroom closet at my parents' house. The old Estes launcher was partially there. I could not find all of the parts. I don't even remember taking it apart. I also found my two Estes Pola-Pulse launchers which used a flat Polaroid battery that was only in production the week I bought the launch controller.
During the 20 years since my first rocketry career I had worked for an electrician and got to know heavy duty electrical components. I decided it was time to build my own launcher out of real electrical components with the help of my sons.
The components: 6x6x4 inch PVC junction box, 100 feet of 14 ga. electric wire for low voltage garden lights, generic 12v side marker light, generic tractor ignition switch, generic push button truck starter starter switch, strain relieving watertight non-metallic cable connector, male GM weatherpack connector, female GM weatherpack connector.
The components out of their packages.
Junction box marked for drilling.
1st June 2010, 04:12 PM
A knot to provide additional strain relief.
Yes, I solder all of my connections, even my crimp connectors.
All put together.
A close up of the box.
The GM Weatherpack connectors are used to join the lightweight wire with microclips to the heavy duty cable.
To ensure the launcher lasts a long time I sealed all penetrations of the box with silicone sealer. I wish I had a dollar for every nice day I set out to launch rockets which turned into thunderstorms.
1st June 2010, 04:39 PM
The components which came from Home Depot; junction box, 14 ga wire and strain relieving connectors. The rest of the parts came from the local automotive parts house. The lightweight wire with the micro clips was salvaged from the obsolete Pola-Pulse launcher and the battery clamps with cables were salvaged from a scrap heap.
I initially set out to buy 30 feet of 16 ga. cable but I found the 100 foot coil of 14 ga. cable at Home Depot marked down because it was out of package. I got 100 feet of 14 ga cable cheaper than 30 feet of 16 ga cable would have cost. The 100 foot cable conducts enough juice from a very weak 6v lantern battery to ignite Estes igniters.
The truck side marker light came with 12v bulbs which conducted enough current to ignite the Estes igniters with a continuity test. I switched in 6v bulbs which will not allow Estes igniters to ignite until I press the launch button and also shine brighter for easier visibility on a sunny day. The 6v bulbs so far have withstood a few launches of Copperhead igniters and First Fire Jrs. But I am still uncomfortable with running 12v through 6v bulbs.
The first diagram below is a schematic of the launcher as built.
Second diagram is my proposal for a dual voltage launcher. Currently I just turn the ignition switch forward to the "Ignition" position and press the launch button. That leaves two switch positions unused: "Acc" and "Start". I am going to buy another ignition switch (they only cost $8) and dissect it see if some surgery will allow me to use the "Acc" position for 6v launches, the "Ignition" position for continuity tests on 12v launches and the "Start" position for firing 12v launches. This would require both hands on the controller for 12v launches, an added safety measure.
By the way, how would I calculate what sized resistor I need for the 12v version in Schematic2?
1st June 2010, 05:15 PM
I did not see details on the key, but I assume it is the safety interlock. Hopefully it can only be removed when in the "off" position so the system cannot be left locked in a live condition.
As for bright continuity lights that will withstand a range of voltage and not pass much current (and be safe for Q2G2 low current igniters), check out the superbright LEDs available. For standard Estes controllers, the LED replacement of choice is this one:
1st June 2010, 05:30 PM
Fred, thank you for the advice about LEDs. The local auto parts store has a version of the side marker lamp with LEDs and is substantially similar enough to the incandescent version I used that I can just swap one in. I may do just that but that would be too simple a solution for my tastes.
And yes the key can be removed only when the ignition switch is in the off position.
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