Tuesday, 16 August 2011

The first of manny tests

We conducted the first test on the weekend and it was successful, and although I didn't get all the tests I wanted to do done due to a technical issue with the relay box overall it was successful. As I will discuss there is much to improve in the way of safety and organization.

I wanted to do three tests on sunday:

1: Filling the nitrous tank remotely, and venting it using the actuated valves.
2: Filling the fuel tank, filling the nitrous tank remotely and then venting and igniting the propellants
3: Same as #2 but with combustion chamber on (very short duration test)

Test #1 went as expected. After opening the nitrous fill bottle valve and retreating I opened the vent valve, fill valve and then closed the vent after about two seconds, followed by the fill. I then opened the oxidizer valve and Hissing was heard as the nitrous vented through the injector block. One thing that became very evident was that it is very difficult to keep track of the valve position in your head, especially in the heat a first test. I had two buttons, one to open them 1/10th and one for full but between watching and listening to try to see what was happening I completely lost track of how manny times I opened the valve. Not a really big issue as it it can't go past open, and to be sure they were closed I closed them a few times but for the next test I really need to have feed back on them. Just a potentiometer, coupled to the motor shaft will work well.

Test #2 started well, I filled the fuel tank roughly 1/4 full of ethanol, opened the pressure (argon) and nitrous bottles and retreated, after arming the igniter which was installed just past the injector block. As with test #1 I filled the nitrous tank. I then pressurized the system then ignited the igniter. After seeing that the igniter did ignite I opened both fuel and oxidizer valves but nothing seemed to happen. I was still getting confirmation that the mirocontroler was receiving commands but the valves (and nothing else) wouldn't respond. After waiting a bit (not long enough) we approached the stand and found hissing from the top of the fuel tank (the vent line at the flare connector to tee adapter) and in the female-female adapter on the top of the ox tank. We did pressure test with 120PSI air after setting up and didn't find any leaks but the lines probably came slightly loose during the bumpy drive. After the tanks had emptied (I manually vented the fuel tank, and we waited for the ox tank to vent) I could all the sparkfun type relay boards to be unresponsive. The ones rob made with the DPST relay and reed really were working, so I could close the valves but not open them and nothing else worked as they all used the spark fun boards. I haven't had time to diagnose the problem, but it seems like the transistor that switches the relay had blown on every board. I don't understand how this could happen, as they are all wires in parallel, but ariel thought that the ignitor could have acted as a big inductor and fried them. This is consistent with the fact that everything stopped responding just after the ignitor lit. Unfortunately I don't have the burnt ignitor to see if it burnt through, or if the relay stopped working before it got enough power to burn through. Marco and I worked for about half an hour trying to diagnose the problem while burn and ariel fixed the leaky pipes but we couldn't fix it and it had started to rain so we decided to move the trailer back to the main road and try to fix the box in our car while the rain passed. I couldn't so we packed up.

Although I had a rough idea of the things I wanted to do on the day of the test I didn't have a set plan, and I   learnt a really important lesson about the complexity of running a test. I future I would like to have a plan of the test in detail including different scenarios like the weather, failures etc. The weather coindincentally was something I had given no thought to and when we saw rain coming we just said....well better hurry up, which was entirely the wrong decision because we were then rushing. Organization of tools and parts was another area for significant improvement, as we misplaced tools manny manny times. I hadn't given any consideration to balancing the trailer and we ended up using a spare argon tank to weight the trailer, which one time in the rush before a test I removed, only to have the trailer tiped over (i cut my finger quite badly In the process which was very distracting when it came to the test). Rushing I think was the thing we did the worst, and I think this was a combination about not really having a set, rehersed plan, the weather and being generally nervous and wanting to get it over with.

The main safety issue I identified was when the test stand stopped responding, and we approached the stand with the tanks partially pressurized (although not fully because of the leak). For this I need a backup remote venting system. This can be as simple as string attached to valves. Test stand stability was the other. The other thing was fateuige (of us). I had thought of every possible spare tool, spare part and piece of equipment to bring (preparation was one thing well done) but the things we needed: Food, water, sunscreen I neglected. I was getting really dehydrated towards the end of the day because I didn't bring any water, and I think everyone was getting a bit grumpy because of the lack of food.

Also the drive was long and quite rough, although the test stand held up quite well accept for the two leaks. In future I would like to do a high pressure test on site. I was hopeing to avoid this because it uses a lot of argon with the tanks empty, but is necessary. We did have an issue with one of the tank mounting points cracking during the drive (the scrap piece of metal I used was apparently cast iron), but we just strapped it up and everything was fine. Both these will need to be replaced before the next test.

Technicial issues which need to be resolved:

1.Key in fuel valve needs to be thicker as it fell out and we had to apply a temporary fix of tape and plastic.
Valves need feedback

2.Need to install pressure transducers (already have them) so tank pressure can be confirmed as empty before approaching stand

3. Valves need feedback.

4. Need to have a isolated igniter circuit, with separate battery so it can't interfere with the control circuit. Would also like to have a backup ignitor system.

5. backup venting system

Organizational issues:

1. Need to have a written operations plan for the test that includes:
-A procedure for the setting up - With checklist
-A procedure for pre test, test and post test
-A procedure for dealing with weather, and unexpected outcomes (all of them!)

2. Need to rehearse the test before hand so everyone knows exactly what they need to do

3. Need to consider other test aspects other than just technical.

4. Have a extra table for tools etc at the test site and things neatly organized (rushing didn't help)

5. Not rushing

6. Get a good nights sleep!

Hopefully we can get a test site that is closer for the next test. Driving slowly with the trailer it took about 2.5 hours just to get to the site. The drive alone was quite taxing. Andrew suggested I try talking to some people with more experience to develop the operation plan, which is a good idea.

The videos of the actual test are quite uneventful, and all you see is some lovely clouds in the background accompanied to loud hissing. I won't bore everyone (unless they want to see it) with the video of the two tests but here is a quick video of everyone setting up.

I have been a bit critical, but overall I would say that the test was a success as I showed that I could remotely fill the nitrous tank and vent it using the actuated valves. Considering that this is the first test we have done on this scale and complexity I think everyone did really well, and I would like to thank Buren for all his help over the last 8 months. Also tanks to Ariel for his help through countless conversations about electrical aspects ( I would ave been using either a really long lan cable or a wifi antenna with directional antennas is it went for you!) and for his help on the day. Stewie you were also a grab help with the relays and strain gauge amplifiers it would have taken me quite a lot longer to understand the amplifier circuit. Also thanks to Marco, (who I can say was probably the only person thinking straight on the day) for his help on the day and help and advice and encouragement over the last 6 months. Thanks to Andrew for your help, advice and encouragement.

No comments:

Post a Comment