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PWM Driven Estes Rocket Ignition Circuit

posted Mar 10, 2015, 12:10 AM by Neil Caulfield   [ updated Mar 10, 2015, 12:31 AM ]
Timeframe: 2012 - 2014
Requirements: Analog circuits, soldering, PCB design software, Arduino programing

This circuit was developed in collaboration with Mike Dipalo (his work here) over about 2 years. I did the circuit design work, while he created the code needed for the circuit to function properly. 

The circuit works as follows: The Atmega chip "listens" on the PWM input from an RC radio for the signal to pass a certain threshold. When this threshold is passed, start individually closing four ignition circuits at 1 second intervals. When the counter has cycled, start from circuit one again. If the input signal goes below the threshold(LOW), the entire process will stop, and resume when the input is HIGH again. 

The idea behind this circuit was to make realistic scale aircraft that were capable of launching scale missile payloads. While this idea is frowned upon by some in the radio control community, there are no laws against it. It is, however, against AMA (Academy of Model Aeronautics) rules to launch a rocket motor from a larger moving model. This only applies to AMA sanctioned flying fields.

Early board prototypes began in March 2012, with the final model being produced in late 2013. The board had a total of 4 different revisions. All four were capable of launching from 4 channels in sequence. 

Rev 1 (labeled prototype): Perfboard with relays connected to arduino
Rev 2 (labeled version 1): very large circuitboard with lots of unused space
Rev 3 (labeled rev 2): much smaller, new etching service for less cost, traces were too thin and burned up
Rev 4 (labeled rev 2.1): same as previous version, but traces were edited to be thicker, and the board's color was changed to make it easily distinguishable. 

The videos below are tests of the second, third, and fourth revision respectively. If you had to watch just one, the second video is probably the best. 

Second Revision 
Third Revision
Fourth Revision