I've been flying rockets since 1995 and flying mainly high power since 1999, but during all this time I've only ever owned the Estes Electron Beam launch controller. It's only designed for launching single engine model rockets and isn't really suited to converting into a high power launch controller. I've been saying that I'll build proper high power launch controller for years, but I've just never got round to it.

I've finally decided to bit the bullet and build one, so I thought I'd share the design and construction of it. There are a number of factors to take into account when building launch controller and I hope to address them all with this design. Above all, it's got to be simple and easy to use, but safe enough that you can't accidentally set off an ignitor.

One of the main problems with home built launch controllers is over complexity. There seem to be many controllers that I've seen that have loads of plugs and switches on them, buzzers, flashing lights and other bits and bobs. As with building certification rockets, you should follow the KISS principle, Keep It Simple Stupid.

To ensure that this controller is as simple as possible, I won't be putting any continuity circuitry, flashing lights or voltage readouts on it. Checking the continuity of your ignitors on the launch pad with the ignitor in the motor is not the greatest of ideas. Using flashing lights or buzzers can be bad as well as many have current draw that is greater than the guaranteed all fire current of some ignitors.

At this point you might bas asking yourself why a continuity circuit is a bad idea when so many people have then in their controllers. Let me put it this way, you've just spent a while preparing your rocket for flight, you've built the motor, packed the parachute and taken the rocket to see the RSO. Now you stick it out on the pad, stuff an ignitor in it and wait to be given the all clear, but you don't get continuity when you check. Now you have to go all the way back do to the rocket and make sure you connected everything up correctly. You did, so now you have to go and get another ignitor and repeat the process.

It would have taken you 20 seconds to dig out a multi-meter when you were preparing your rocket and check the ignitor for continuity. If you fly dual deployment you should be checking the ejection charge ignitors anyway, so how much longer would it take you to check the motor ignitor? Checking the continuity of your ignitor on the pad is not the correct way to do it, so you don't need a continuity detector in your controller.

One final bit of safety consideration is the battery re-charging point of the controller (if there is one). There have been a number of incidents where people have accidentally connected their ignitor to the battery recharging point, thus setting it off, this also applies if you use an extra external battery. The easiest way to get round this is to use different connectors for different things, so that there is no danger of you plugging things into the wrong sockets. So the controller I am going to build is going to be simple, no continuity circuit, no flashy extras and using different connectors of ignitor terminals and battery re-charging points. To this end, I've come up with the following simple schematic:

As you can see there are two components, the handset and the main box. The main box will be out by the pad and contain a sealed lead acid battery, while the handset will be on 50-60 metres of cable to enable the launching of most high power motors from their safe distance as laid down in the UKRA Safety Code.

The parts list will be something like:

• 1 x weatherproof metal box
• 2 x push button switches
• 1 x key switch (key only removable in one location)
• 1 x PP3 battery compartment
• 1 x Female XLR socket

• 2 x Male XLR plugs
• 60 metres 2 core cable
• 1 x cable reel

• 1 x weatherproof box
• 1 x sealed lead acid battery
• 2 x terminal posts (for ignitor outputs)
• 2 x sockets for recharging point
• 1 x Female XLR socket
• 1 x 40A automotive relay

You might be wondering why the handset has two push buttons on it? The reason is safety, because they will be on opposite sides there is no chance of accidentally dropping the handset and it setting off the ignitor by pressing the only fire button, as both buttons need to be pressed at the same time. It's small things like this that keep a controller simple and safe, the two most important things when building any controller.

I haven't bought any of the parts yet and I'm not sure when I'll get round to it, but I'm thinking I might build it during the UKRA 2003 event. The main reason for this is that there will be a bunch of electronic gurus there who I can lean of for help if needs be.

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Last update: Tuesday, 30-Mar-2004 03:47:44 EST