Saturday, 15 September 2012

Second teathered flight test

Yesterday (Saturday) we tried another tethered flight test. The main aim of the test was to test the roll control program. The test went fairly well but after warming up the engines and dialling in the correct amount of thrust so the vehicle would just list off we only got a few seconds of auto hover before the peroxide ran out which wasn't enough time to see if the program worked. The thrust was also a bit low so although it did look like it was stabilising itself it didn't actually lift off. It was dark by the time we had vented the tank so we decided to pack up and try again next Sunday.

We had a few issues with the vent solenoid during the test. I accidentally installed it the wrong way around when installing the quick disconnect earlier in the week and because it only seals one way, when the quick disconnect released for the first time so did the pressure in the tank. We switched it around which was not the best safety wise  as although the tank was pretty much depressurised the vehicle still was filled with peroxide. Also because the new line we are using to pressurise is so small (1/8") it takes ages to fill and we burnt out the solenoid when filling for the first time. I decided just to not use it after we had fixed the direction problem (as we don't need the vent solenoid to fill, its just quicker when its open and reaches a slightly lower pressure) which only meant that we couldn't vent at the end of the test without dumping the rest of the peroxide. The pressure transducer was working for this test which was useful good because filling took so long. I had been having great trouble getting it working (reading the transducer voltage), I eventually figured out that my particular Arduino clone needs its VREF pin connected to a something (5V) as the internal VREF doesn't seem to work or is set very low.

Burens quick disconnect worked brilliantly and was probably the best part of the test. When it was fired it came cleanly away and retracted to the top of the stand. Here is a clip of it in action:

We also tried out Sam's GUI control program which looked great but had a few teething problems. It seemed to work well when testing before the test but when we tried it out it was cutting the time of the commands short by one digit so we just switched back to manual commands. I am looking forward to using it for the next test as it makes control much easier than typing out strings and also eliminates errors, it is easy to put an extra 0 on the string and send a pulse for 10 seconds instead of 1.

It is about time we fixed a few minor annoyances on the vehicle. Firstly we need a bettwe way to mount the control box. At the moment the box is screwed together from its underside then bolted to the vehicle. We need to take it off and open it quite a bit and screwing and bolting takes a long time so I usually just tape it closed and zip tie it to the rocket. It would be great if we could just clip it to the rocket. Also it is annoying to have to open the box every time to get the SD card out. A sd card extension cable is one option but a simpler idea would be to just add in functionally to download the file from the controller after the test. We might be able to do this over LAN because the Arduino has a ethernet port on it. Another thing that is annoying it how we fill. At the movement we fill with a funnel through the front 1/4" port and just before the test screw in the pressure relief plug. The port is in a bit of a awkward position and it is difficult to fill and install the plug. Also we ahev to put thread tape on each time and occasionally when unscrewing a little tape gets in the tank. It would be great to have some sort of quick disconnect system where we can just pop off and on the plug and having the filling stem out from the tank.

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