Having recently purchased a starter kit for an Alpha III Model Rocket I was unfortunately underwhelmed with the controller supplied in the kit. The main issue for me being the standard 9volt battery not producing enough power to the igniter to effectively light the engine and launch the rocket. The supplied controller is otherwise a good design (maybe a little flimsy) with the removable safety key which is great feature especially when children are around the launch area. The other problem is, well if your anything like me you will have no trouble losing that particular safety key. Instead of a removable key i opted for a dual action toggle switch and removable launch leads for safety.
My answer to the main issue was to build a more robust unit and beef up the power delivery. I was able to produce the following controller for around $35 including the Li-Po battery. Most of my supplies were purchased at my local Jaycar but I'm sure you could lower the costs buy purchasing online.
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Step 1: Collect Your Materials
All materials are shown in first photo except for the Zippy Compact 850mah Battery and panel mount fuse assembly which were added after my first version failed to impress with a standard 9volt battery.
- project box/ adaptable box (I used a 125mm x 65mm x 40mm box)
- toggle switch
- carbon missile style toggle cover
- red LED momentary push button
- battery (please check above link for the Zippy compact battery used)
- panel mount fuse holder
- 5amp glass fuse (added for short circuit protection with the inclusion of the LiPo battery)
- panel mount banana sockets (red & black - optional)
- 1mm flex building wire
- right angled spade lugs
- heat shrink (tape could also be used)
- twin cable such as speaker wire with banana plugs at one end and alligator clips at the launch pad end
- pliers for cable stripping and crimping lugs
- battery drill
- 13mm drill bit
- 6mm drill bit
- 20mm holesaw
- gas torch (if heatshrink is used)
- soldering iron & solder
Step 2: Preparation and Layout
Firstly I cut all of my cable to length and applied the relevant lugs and heat shrink. Also you may like to solder connections to the panel mount fuse and banana plug sockets prior to installing them in the panel.
Coming from an electrical background I'm big on insulation so all connections I have used heat shrink. You could also use plain insulation tape or not worry at all as long as clearances are ok at the component terminals.
You will also need to take your length of twin cable (speaker cable) and solder your banana plugs to one end and alligator clips to the other. The length of cable you use will depend how brave you are but I recommend at least 3-5 metres.
The exact layout can be customised to suit yourself. I decided to make mine like a playstation remote with a horizontal layout as seen in the intro picture. The toggle switch mounted to the left and the pushbutton to the right. The panel mount fuse is located in the middle towards the front edge.
The Toggle switch and panel mount fuse require a 13mm hole drilled, the pushbutton is mounted with a 20mm hole drilled using a hole saw. The banana plug socket are mounted on the leading edge of the controller and require a 6mm hole.
Depending on the Project box you use you may need to be fairly exact with your layout making sure to allow for battery installation and still being able close the lid once all is complete
Step 3: Circuit Wiring
The wiring required is very simple and all the information required should be found in the attached pictures. My apologies for the rough wiring diagram, it is only intended as a guide and the symbols used may not be exactly right.
Step 4: Completion and Test
Assuming you have arranged and wired all the components correctly you are now ready connect your battery (as an extra I made a small notch in the side wall of my project box to all for the charge/ balance plugs of my battery to be accessed externally), close your project box or should I say Launch Control Box and test your circuit.
You will have to attach your twin cable with banana plugs to the sockets mounted on the box and the alligator clips to a suitable size resistor (test purposes only) or sacrifice an actual engine igniter. If all is well what you will see should be something similar to the attached video clip.
Congratulations! you now have built a fully functional, powered up ignition control for you model rocket, now all that's left is to get out in the field and launch some rockets.