My name is Douwe van Willigen and I am a member of the electronics team of DARE. Since the failed launch attempt of October 2014 we have been working hard on improving the systems in Stratos II+ to make all the systems as reliable as we can.
One of the systems that we have improved a lot since last year is the Engine Control Unit. This system is used to control the valves and servos for the motor contains the Flight Termination System (FTS). The ECU used in the previous launch attempt was produced under quite some time pressure, which meant that compromises were required. But now that we have implemented the lessons learned from the launch campaign last year, I made sure a system was designed that is free from compromises that should work flawlessly.
Aluminium Enclosure
The Engine Control Unit is located between the oxidizer tank and the combustion chamber, in the coupler. Now a problem that arose during the launch campaign last year was that accessibility of the ECU, at this location, proved to be poor. To address this problem we altered the design of both the coupler and the electronics. I CNC-milled a robust aluminium housing that protects (and shields) this critical piece of electronics and allows the entire ECU to be easily removed from the rocket.
ECU enclosure during production
The enclosure fits snugly inside the coupler, whilst leaving space for all the hoses, valves and servos. It also includes a compartment to hold the two batteries that power the electronics during flight (under the lid behind the red wires, see below).
The engine control unit mounted inside the coupler
Printed Circuit boards
The semi-circular shape of the aluminium housing meant we required circuit boards of a special shape (as seen in the pictures). Eurocircuits kindly sponsored us the circuit boards that we designed to fit in the enclosure.
A closeup of the engine control unit moisture sensor
During the launch attempt in October 2014, we learned that easy access to the engine control unit is very important during operations. Therefore the new design has additional features to improve the ease of handling the ECU. A programming and charging connector are accessible from the outside of the rocket, eliminating the need to disassemble the motor bay when a software update needs to be performed or the batteries need to be charged. Furthermore, to easily see the states of the Flight Termination System, a tiny display is added to visualize all the important information of the system when it is not connected to a computer (for example when we are performing tests).
Accessible programming and charging connector (left hole) and status display (right hole)
One more system ready for flight!