Monday, 8 October 2012

Fourth Test

Yesterday we tried a test of the attitude loop. I made a mistake when implementing Barts controller and as a result the vehicle didn't really show any control.

So we didn't really learn anything new control wise, except that if you have to reverse inputs to get the outputs the right way around there is probably a another problem. One of the issues we had in previous tests is that the rocket was always swinging when starting so had sideways velocity which caused it to drift and as a result it was difficult to see how much control it had. This test we used stilts to take off from which would then fall over from the exhaust.

They were too tall and the vehicle fell over once when pressurising and once when warming up the thrusters. It was a really windy day but the legs do need to be shorter and probably wider. This means we need to lower the vehicle. Our aim for future tests is to load only enough peroxide for a few seconds of hover and only test from the platform. This will ensure all tests are consistent in terms of pressure, orientation and velocity at take off.

When it was clear that the vehicle had no control we decided to do a through test of all the engines by pulsing them individually. It seems like there is a problem with engine 2. We are going to do some flow rate tests on Tuesday and will probably take it apart. I do remember it having less compression than the other two because the injector was slightly. This would cause a lower pressure drop and a higher flow rate which is what we are seeing.

At some stage we will probably need to take all the engines off and test them on the test stand to get better data on their thrust response. This will involve making a new test stand as the one we have now never gave very good results. There are a few reasons but it was not designed for the current engine and the engine is not restrained well. The new one will be test the engine vertically because the engines seem to behave differently vertically compared to horizontal. I also know much more about the thrust settings we need for the vehicle.

Buren and I also did some experimenting with methods of making plastic bladders from plastic sheet which could turn our flight tank into a positive expulsion tank. The idea is to insert the bladder and tube into the top 3/8" hole so we don't have to open the tank. We first tried joining PE film with a flame then with a hot edge which didn't work particularly well as the film would just melt. We then used hot glue which worked really well with a edge to press tow sheets together. We managed to make a fairly good bladder using this method. On tuesday night we will try butting it into the test tank we blew up. Teflon film/sheet seems to be fairly available so thats what we would use for a peroxide compatible bladder. I was thinking about also buying a plastic welding gun so we could use use polyethylene or another plastic to weld it together. It would be easier to join the sheets because the teflon wouldn't melt. The other method of joining would be epoxy but I don't think we could keep it all together well enough while setting. We have only been making "pillow" bladders so far but we are aiming for something like this eventually:

No comments:

Post a Comment