Thursday, 15 September 2011

I have been quite busy with uni and work over the last two weeks but have tried to find the time to finnish off the things that need completing before the next test.

I had planned on conducting a test this weekend, but for a number of reasons it was postponed to next saturday. Although I am keen for another test it was probably the right decision to postpose the test, because although I could have probably got the electronics don't in time one of the things that was done poorly in the last test was rushing, and hopefully I can have everything done this weekend so I will have one week to double check everything is working (100% !)

In the way of electronics I have:
  1. Installed the new relay bank - Much much neater now. (diagnosing was a problem at the last site and I have a spare it can be swapped out with.
  2. Installed the speed controllers
  3. Made 12v and 5v regulator boards for the router and usb server
  4. Tested the trimpots and started making their breakout board
  5. Tested the pressure transducers and started making their board
  6. Allot of wiring in-between the new components
I still have to finish the sensor break out boards. Annoyingly the only precision trimpots I could for less than a bizillion dollars find were 10 turn. It didn't say that on the ebay listing but I should have known from how long they were. This means that I only have 1/4 of a volt between the half turn from full open to full close. If the trimpot is +- %5 this means there is 0.25v error (same as the resolution they have)! Although thats the absolute error over all the windings in the pot, and i suspect the actual error would be less (as it will stay roughly in the same position) its still not good. I might pick up a cheap one turn pot (10-20% error that will have less error and more range (1v error of its range @ 20%) which all be better than the 10 turn precision one. I am also having troube with the vregs overheating. I am not exactly sure what current I am drawing but they are rated to 3A and they are getting quite hot. I will have to fix a heat sink, and a big one. Heat could be an issue in the un-ventilated boxes. i also have to wire up the transducers so that the max output is 5v, where the default output is about 6.5.

I also bought two needle valves I would like to connect up after each main actuated valve. The reason for that is I am paranoid that too much propellant will go into the engine during start up with bad consequences. A needle valve will allow me to precisely calibrate the maximum flow.

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