Sunday, 10 July 2011

Precautions and electronics

I have been working on electronics for the last two days and the two electronics boxes and they are coming together nicely. I got these great old ammunition boxes which are perfect for control boxes. Cutting the holes for the connectors with the plasma cutter wasn't as clean as I had hoped for so i had to use a bit of hot  glue to seal the connectors in. I am hoping that the metal boxes will shield the analogue components from any interference caused by the relays.

I am starting to think it would have been better to go with solenoids instead of the ball valves for the main propellant control valves. They are allot of effort and all i am using them for is opening and closing. I am planing on simply pulsing them to move to a particular position. They will jam when open and close so as long as i open it for slightly longer than needed error shouldn't accumulate. When i get around to it, or need it i will add in encoders but for now they are just expensive solenoids.

I have also been doing some reading on safety and material compatibility of N20. Ironically the best reference I have found is a scaled composites document. I am hoping it was written post accident. Anyway i was surprised to learn that the ignitability varies alot with pressure. With epoxy for example at 130PSI 130J are needed to ignite the epoxy but at 600PSI only 6 PSI is needed. I will be using up to 2000PSI. I am not sure what the ignition energy at that pressure is but it might be enough that a valve closing quickly enough could provide it. The valves close quite close but by far the best way of mitigating the risk is eliminating any fuel source. Some potential fuels i have identified are:

Grease in the hydraulic components
Coolant/oil in the tanks i put in to prevent rust during storage.
Hydraulic oil in the plumbing

Also the other way it suggested is to mitigate risk is to give the tanks a vent big enough relief valve that if the nitrous starts decomposing the tanks dont explode. I have inadvertently done this with the design of my tanks. If overpresurisation did occur the bolts holding the caps will shear (which did happen with the origional undersized bolts during testing) and the caps will pop off

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