Introduction: Model Rocket Launch Controller (aka BDC)

I have been browsing through this site for last 2 years or so and have never actually submitted anything. Well during the 2 week snow storm we had, I decided to kill some time and make this launch controller. I've seen a bunch of different plans on how to make these, but I never really liked any of the designs or layouts of the buttons.

I used to make rockets as a kid, but haven't made any in probably the last 15 years. So to get back in the spirit this is what I came up with. (I made this slideshow as an afterthought, so sorry to say no build pictures).The first time my wife saw it she asked me if I was about to rob a bank (Thus the name BDC, Bomb Detonation Controller) , so I'm pleased with the very detonatoresque way it looks.

The breakdown of the whole system is relatively simple. I'm sure most of you can figure it out by just looking at the wiring, but I will break it down to individual components. Total cost of parts was probably around $15 (versus $25 for a store bought controller). This whole project runs from a single 9V battery.

- First is the project box. I just picked it up from Radioshack to enclose all of the components. its the medium sized box

- Next is the interlock safety switch, also from Radioshack. It has a safety cover to prevent accidental engagement and an indicator light which I use as an "ARMED" light. The positive of the 9V battery is soldered to the "power" lead of the interlock switch. The negative of the 9V is soldered to the "ground" lead of the switch. Another ground wire is soldered from the ground lead to the black binding post.

- The ACC lead from the interlock switch is soldered to the momentary ON switch that is used as a "FIRE" button on the controller. Which is then wired to the red binding post.

The circuit, in essence, is a very simple switch circuit. Flip the saftey cover up, flip the "ARMED" switch, and press the "FIRE" button to launch your rocket! I made the wires that lead to the rocket out of some 22 gauge speaker wire and some solder on alligator clips. The wire needs to be at least 15 feet long to keep the user far enough from the rocket to prevent injury. The ends of the speaker wire are stripped so they can be attached to the binding posts.

Note: When I installed the binding posts, they have a metal thread instead of a plastic one that goes through the project box. I had to insulate the threads, with heatshrink tubing, to prevent the hotlead from grounding out on the case.

**This launch controller follows the NAR (National Association of Rocketry) guidelines for an ignition launch controller. Directly from the NAR website: "Ignition System. I will launch my rockets with an electrical launch system and electrical motor igniters. My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the "off" position when released."**


Esteban666 (author)2013-08-01

Thanks for this post chris15252! I teach middle school science and math, and to integrate the two subjects, we build rockets from construction paper, paper clips, and mat board. Each year we launch 100-200 rockets. I got tired of doing field repairs on Estes controllers that get dropped after launch, so I started surfing for alternatives. Your design meets most of my needs as being relatively simple, rugged (hormonal middle school student proof), and  having a certain degree of the "kewl" factor.  It also gave me the opportunity to buy some new tools and practice my soldering skills. EET's design added more of the K-factor, but I decided against the buzzer to preserve battery life. I blow a whistle five seconds before a launch to warn spectators they may need to run for cover very soon.

Most of the stuff I got from Radio Shack except for the interlock switch, the push button momentary switch, and the LED pilot light. These I got from various vendors via Amazon. The 3" cabinet pulls I bought at Home Depot add ergonomics and a convenient place to store the wire. I had to get a little creative with mounting them, but they are solid.  The LEDs are more than bright enough to be seen in full daylight. Be careful ordering the LEDs from Amazon. The picture of the LEDs are all green even for the red and blue lights. Read the fine print!

I wanted the added safety factor of having a key (the binder clip) to be left on the launch pad until the rocket is ready. I toyed with the idea of using a key switch, but middle school students habitually lose stuff, so I wanted something easy to find and something easily replaceable. I filed some flats on the bolts and sanded the inside of the binder clip to ensure good contact. I'll eventually add string and some surveyors tape to the key to help find it in the grass and double as a wind sock. I think it adds a little more K-factor.

The LED acts as a continuity indicator just like the light in the Estes controller. This can be a little tricky because that only a small amount of current should be available for the LED so that the igniter is not fired. Using a (V battery and pressing the launch button, the circuit lighting the LED has 4.43 volts and 1900ohms of resistance. Adding the resistance of the 9V battery gives me a measured current of 6.1 milliamps. This is significantly less than the continuity current in the Estes controller of 99 milliamps meaning that it is even safer than an Estes controller in this respect. An Estes igniter requires at least 2 amps of current and my multi-meter maxes out at 1, but Ohm's Law predicts a current of 3.14 amps. I've tried this controller out a few times with no problems lighting the igniter.

Some sites suggested a recessed launch button, but I find them to be awkward and redundant considering the key. I'll try out the big red buttons and switch (pun intended) over to a recessed button if the students complain enough or if there's an accidental launch. I'm concerned about battery life using a 9V, but I can always change to a 1.5V battery pack. There is plenty of room in the project box.

We design rockets and cut parts in the fall to learn the metric system and practice decimals, but don't assemble and launch until the last week of school. I'll post again once I really put this through its paces.

Top off.jpgTop On.jpgTop on igniter.jpgSide.jpgTop.jpgInside.jpg
EET1982 (author)2012-08-06

Got mine done. Haven't tried it out but I'm sure it will do the deed. I also put a buzzer on the launch switch just for kicks. Thanks for such a cool 'able!

chris15252 (author)EET19822012-08-07

Sweet! That came out great and I really enjoy the pictures. I also do like the armed light you have installed on the housing, nice little touch haha. I'd love to know how it worked for you once you've tested it!

jscibelli (author)2011-06-17

can you use screws instead of the big red and black things for the wire

chris15252 (author)jscibelli2011-06-20

Sorry for the late response. Yes you could use screws in place of the binding posts, but they need to be insulated from the metal cover of the project box (if yours has one) and away from other wires. I use the binding posts because they are easy to wire and they give a good solid place to attach the launch wires to. Hope that helps! Thanks

clzfishing (author)2011-03-10

I was wondering if you could help me with your design because I want to use your system but incorporate it so it has six detonation switches. So what I want to do is be able to controll six rockets instead of just one. If you have any ideas to help me please reply so I can use this be July 4th.

chris15252 (author)clzfishing2011-03-11

Adding multiple launch switches to the circuit wouldn't be too difficult really. But it depends no if you want an interlock switch (the red cover switch) for each launch connection or if you wanted one interlock and just multiple launch switches with multiple posts. I created a schematic for multiple launch buttons and one interlock switch (ignore the fact that I'm terrible at drawing schematics. Also ignore the black connections on each binding post, my cad software only has dual binding posts). Basically you would just wire multiple push button switches in series that go to a separate red binding post. You could use the same ground for all of the rockets. The only problem is that you could only launch 1 rocket at a time using a single 9V battery. See the schematic here:

clzfishing (author)chris152522011-03-12

Would any hobbyshop have a project box like the one you used. And do buoy recommend I use a larger box like 2 or 3 times the size? If so give me the dimensions of yours for a reference.

chris15252 (author)clzfishing2011-03-12

I bought my project box at radioshack. I really don't think they have any larger ones than the one i used though. The dimensions of mine are 5" long 2 1/2" wide and 2 1/4" deep. I think at the most you might be able to get 3 more buttons and posts on that size box, but it would be pretty crowded. I really wouldn't know of anywhere that would have a larger box, sorry to say.

clzfishing (author)2011-03-11

For some reason I could not upload your design but my idea for the red trigger guards I would only guard the toggle switch it's self and then under that there would be a red light to tell me that that switch is armed. Does that seem logical or would that not work for my design????

chris15252 (author)clzfishing2011-03-11

The toggle interlock switch in my design has a red "armed" light already built into it. So when you flip open the cover and flip the switch a red light on the end of the switch lights up. An armed light could easily be added to the circuit if you wanted to add one though. Just simply add it in between the interlock switch and the push button. The best I can do is add a clickable link to this post for the schematic, if I attach it you wont be able to see it. Try this link:

About This Instructable




Bio: I'm a mechanic and a tinkerer. I was always that kid that took things apart and put them back together just because I could ... More »
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