Tuesday, 27 December 2011

Today I spent a long day organising the workshop. Its still not completely functional, but its getting there.  Organising is really an evolution, and is something that you have to give a bit of throughout to and learn to use if you want to be functional not just look pretty. At the moment we have more space than we know what to do with but I am sure that will change once we get used to working in a bigger area. Its strange having to walk for a good 20m to wash your hands.

I am still working on the sparging setup. I have moved from a comum made of PVC to a hot water urn, and now to a stainless keg.  Last night I thought I had everything ready for a first batch using the urn. The setup was working well with water, with no impurities in the water after a few runs. I cleaned everything then added a small amount of peroxide to the urn which started fizing immediately from one section of the heating element (while it was off). I think that the element must be braised with something containing a incompatible material (silver?). I also found out that the heating element was not stainless but copper coated in stainless when a bit of the coating flaked off. I am running some tests with a 19L keg now. The heating always a issue. At the moment I am heating the sparging air with a air conditioning condenser in the urn, as well as the keg with another electric heater. One thing I learnt from the PVC tube is that you want the number of things in contact with the peroxide to be kept to a minimum, so you really need to heat from the outside. I am thinking of immersing the keg in a water bath but that seems a little messy. Heating the air is a more elegant solution but even with the air piping hot it barely warms the solution, and it takes quite a while to heat up.

I plan to do a compatability test with the keg wendesday and if everything goes well I will line the clean area with plastic and concentrate the first batch. I would like to set everything up so that I don't have to transfer any peroxide between vessels  myself while sparging. The great thing about using a keg is that it is concentrated in the same vessel it will be stored in. I haven't figured out how I will transfer the peroxide out  of the keg for use. It has two connections on it, one for liquid out (has a tube going to the bottom of the vessel) and one for gas in. I will probably have a small hand pump to pump air in to the keg once I close the lid which will push liquid out of the liquid fitting. Usually carbon dioxide is pumped into the vessel from a cylinder.

Wednesday, 21 December 2011

Successful lathe move

Having learnt my lesson from the unsuccessful lathe move of last week, I decided to hire someone who had moved lathes before and did know what they were doing for the second attempt at moving the lathe. This time round there were no issues.....

I am having quite allot of trouble with peroxide compatibly. I used only materials that were compatable (PVC, SS and PE), cleaned meticulously, rinsed with distilled water, then acid and still I get a stream of bubbles. At the moment the sparging column is a PVC pipe, but I am thinking I will switch to all Stainless. At the moment I am pumping warm water from a hot water urn through the column to heat the peroxide, but it occurred to me that I could just use the urn (which is all stainless) and save myself quite a bit of trouble. I will have to replace the seals with viton for compatibility and replace the tap but that should be it. The one downside is that it has a short aspect ratio which wont give much time for the air to be in contact with the solution but the vapour coming off seems saturated as it is so I dont think this will result in a loss of efficiently.

Here are a few pictures of the final PVC concentrator. The three barbs which can be seen are for heating water in, out and air in. I used sprinkler fittings to spray air, which allows for easy adjustment.

Tuesday, 20 December 2011

Its been quite a while since my last post, and things haven been progressing quite as fast as I had hoped, but I thought I would post an update of where we are at and what we are working on.

We have spent most of the last two weeks moving into the new workshop. As all of the shelving and cupboards I had in my old workshop belonged to my parents, we didn't really have anywhere to put things and everything was on the floor for a while which made it very difficult to find things. ABSOE kindly donated some shelving which was a big help and things are now allot neater, although there is still a way to go before we have a completely functional workshop.

We moved the mill in but there was an incident moving the lathe. I hired a chap to move it and short story, he dropped it. He hadn't moved machinery before, which become evident quickly and he was trying to drag it along my wooden garage floor with his crane and a rope tied to the bed. Any person with half a brain could have seen that if you try to pull something that is top heavy from its top it will fall over! Unfortunately I wasn't paying close enough attention to him to stop him. I should have said something when he tried to sling around the lead screws but he got annoyed when I suggested a better way so I tried to stay out of his way, figuring he probably knew what he was doing. There is a lesson there. the damage isn't too bad, a bent lead screw and few broken hand wheels, which I should be able to get spares for. I am slightly worried that there might be more extensive damage to the bed, like a crack but it seems to slide the same and it is not misaligned. After he dropped it he had the nerve to say that it was my fault because I should have been there supporting it as it fell over. I told him if I had I would be underneath it. He diffident have in insurance and I doubt that even if I took him to the small claims tribunal and won, he would have any money to give me. I have definitely learnt a valuable lesson. The thing that is most annoying is that I will be without  a lathe for months. One of the good thing about being in an industrial area is that everything you need is close by. We borrowed the neighbours forklift to move the mill in.

I am close to getting my peroxide concentrator up and running. I have built and tested a prototype sparging setup and have all the parts for a second version. I decided to peruse two methods for concentrating, sparging, and vacuum evaporation. I haven't started work on the vacuum setup but will start after the sparger is up and running. I decided to try a vacuum method to see if I could avoid some of the losses ascoaited with heating the peroxide for sparging. I have a really nice oil free vacuum pump/compressor which should be good for both setups. because the concentrated peroxide doesn't have a good shelf life I plan on storing it frozen or in a fridge. I have so far only been sparging water as I don't currently have a space clean enough that I would feel comfortably handling peroxide in.

We moved the test stand to the workshop on the weekend, and we are currently getting it ready for another test. All that really needs doing from a mechanical perspective is replacing the actuated valves with solenoids, and calibrating the flow rate with needle valves installed before the valves. The software needs a bit more work. I am a bit torn between getting  the engine I spent a long time working on running and getting peroxide production going. I guess I should probably finish what I start, before moving on to new things.

Sponsorship from ABSOE Business Equipment.

A big thanks to ABSOE who have kindly sponsored us by giving us some industrial shelving. ABSOE is a Brisbane based business that specialises in new and used business equipment. They have a huge range of office equipment & fittings, shelving, storage, shop fittings and solutions. They also have a huge building, which used to be an old ice cream factory which is interesting to look through.

Wednesday, 30 November 2011

Its been quite a while since my last post, but don't get worried things are still happening!

I am still working on a peroxide concentrator, but I have decided not to publish any more particulars of my work because of a few reasons:

1. Its really really dangerous:
I didn't really realize when i set out just how dangerous HTP can be if you don't know what you are doing.  I have done a bunch of research and the more I do the more I realize just how dangerous peroxide is! It can be done safely with the correct precautions but I don't want to encourage anyone to attempt it if they haven't researched it for themselves.

2. Its really dangerous!

That said I am looking at using a air mover with steam to vacuum evaporate (not distill) a peroxide solution. Using an air mover was a brilliant idea that my friend Dianne Boddy (a retired engineer) came up with. For those not familiar with an air mover, it works on the same principle as an aspirator (also known as venturi pump) and is designed to propell things along tubes (one application is food in an assembly line).

One of the problems with vacuum evoperation is pulling the vacuum required, but a aspirator should help as it can operate continuously and you can pull quite a good vacuum with one, and its cheap! Usually an air mover moves product along packaging lines, so compressed air is used (to not burn the product), but they typically require quite allot of compressed air to operate so I am planing on using steam.

I had been originally been looking at sparging using a compressor and dry air using a regenerative desicant dryer and a spray syphon (like a paint spray gun) in the mixture to increase mixing of the air and solution (also Dianne's idea). Regular compressors produce air with quite a bit of oil in them, and since organic impurities can cause big problems with peroxide I don't really feel comfortable using one even with a really good filtration system. Instead I would go with a oil free compressor. The sparing system turned out to be quite expensive so I am opting for a vacuum method with a cheap air mover powered by steam.

Another way to use a vacuum would be to suck air through the solution, eliminating the contamination problem.

We have been looking at several workshops in the 100m^2 size to setup a shop. We have decided on a nice little place and are signing the lease this saturday. Here are a few pictures of the place.

I haven't been doing as much rocketry as I would like as I have been working 5 days a week for the last two weeks (to pay for the first months rent and other costs), but I will be cutting it back to 4 and 3 days over the next few weeks. I have mainly been spending my time researching and designing the peroxide concentrator.

I Imagine we will be busy for the next week moving in but after that the two things I will be working on are: getting the nitrous engine ready for another test and the peroxide concentrator.

Monday, 7 November 2011

Some Peroxide experiments

Today I was horrendously bored studying so I did a few experiments on the food grade peroxide.

1. Density: I measured the density with my new hydrometer (set of), and found it to be 1.19, which puts the concentration at about 40-45 percent. I didn't correct for temperature, and it was quite hot in the workshop so it may be higher.

2. Filtering with carbon: I tested pellets of activated carbon from a pet store, used to purify aquarium water. Short story they catalyze the peroxide. I noticed that they didn't start catalyzing imediatelly but only after a few seconds (probably when the peroxide soaked into the carbon). I found out that some activated carbon filters contain a small amount of silver to kill bacteria. That could explain its activity. I have ordered some activated carbon I know doesn't have any silver in it.

3. Filtering with ion-exchange resin: I first tested a very small amount of resin with 25 degree c peroxide to see what would hapen. After a while I couldn't see any bubbles/fire. I put a small amount of resin in a funnel with a strainer at the bottom, and ran through about 100mL of peroxide chilled to about 5 degrees twice. The TDS meter read 0.3g/L before filtering, 0.1 g/l after the first pass and 0.03 after the second pass.  The peroxide was only in contact with the resin for a few seconds each pass so the resin worked extremely effectively at removing dissolved solids. I am not sure what ions the resin have in them, but my guess would be H+ and OH-.

I was going to do a small test sparge with an aquarium air pump I bought. Thinking I might need a bigger pump in the future I ordered a 250L/Min pump. I made a simple sparging rig which was just a bucket with some silicone pipe (with holes in it) to distribute the air. The pump was wawwww overkill for only a few letires of liquid and I couldn't get the setup to not splash water everywhere so I decided that it was probably not a good idea try it with peroxide. I am going to plumb in a ball valve so I can change the flow rate of air.

Monday, 31 October 2011

Error in accelerometer

A Repost of something I did while working on a project a while ago.... Throughout it might be of use to someone.
Today i wrote a fairly simple program to plot position from accelerometer values. It wasn’t too complicated, just a simple python program that reads accelerometer values from the 9DOF accelerometer package (relayed from the ardwino). The hardest part was stripping out the data i wanted from everything else the accelerometer outputs. I had to restart my computer manny manny times initially because i hadn’t figured out how to close the serial stream and for some reason if you close idle with the stream open the keyboard stops working…. I used two of the equations of motion, v2 = v1 + at and s2 = s1 + vt to convert from acceleration to velocity, then to time. There were other methods but this was the easiest to implement.
And what were the results? Not good…….
Here is a plot of acceleration, velocity and position (green, blue and red consecutively) in the x axis Vs. samples (25Hz)  for the acceleration sitting still. As can be seen the error in velocity isnt too bad, but error in position is an order of magnitude more (about 0.25m per second).
I had been hopping for something in the order of a few centimetres per second. This pretty much kills dead reckoning.

Saturday, 29 October 2011

Uni has been hectic lately but all my assignments/thiesis are done so all thats left now is two exams.

I have been learning allot about peroxide over the last month as its the direction I would like to go in. I have managed to find  good supply of bulk %50 food grade peroxide, but it is heavily stabilized.

The first picture is the %50 food grade peroxide. As can be seen it has quite allot of floaties which I believe to be either colloidal stannate or silicate. The bottom picture is %35 reagent grade peroxide as can be seen there are very few particles suspended in it. The few that are visible are a few visible i believe are from not washing the container properly. The reagent grade is probably lightly stabilized. 

I wondered how much the stabilization ada an affect on decomposition, so I did a test comparing decomposition of the two grades. I found out that despite being lower in concentration the %35 it was significantly more reactive when a exposed potassium permanganate catalyst. The first video is of food grade and the second video is of lab grade. As can be seen the %35 reacted faster than the %50

I have ordered a hydrometer so I can measure the exact concentration of the two grades. Using a TDS (total dissolved solids) I measured 0.33g/l for the food grade and 0.26g/l for the lab grade. This was interesting and made me think that the lab grade was more stabalsied than I had initially thought. It also means that the lack of reactivity of the %50 is dependent on the colloid, although without knowing what dissolved stabilizers are present a conclusion can't really be drawn on how much.

For removing the coloid I am going to try a fine carbon filter. For the dissolved stabilizers I will use an ion exchange resign. I have some resin and will give filtering it a go soon, and see what affect ti has on dissolved solids. Ii should be easy to see if the carbon filter has any affect.

I am still looking in to methods for contentrating it. Ideally I would like to use %90 for fuel but initially I all probably concentrate it to %80. A method which seems to be popular in the rocket belt community is distillation under a vacuum. It has a high yield with little loss but also results in the occasional explosion. Normally peroxide vapor at atmospheric pressure will explode, so distillation is done under vacuum at which the vapor is stable. The problem is if you loose your vacuum the peroxide in your distillation column will probably decompose (violently). The articles I have read written by people who produce HTP for their rocket belts all say: design your apparatus for an explosion and stand behind a shield. Everyone who distills peroxide seems to have had at least one explosion. It seems you would have to be crazy to try distillation but then again these are the people that ride rocket packs! 

The other method which is most popular among the amature rocket community is sparing. This involves bubbling a dry gas through the peroxide. Since peroxide has a vapor pressure 10 times less than water the water will evaporate 9 times faster (in theory).

Fractional crystallization (freezing) is another method that doesn't seem to be widely used. It takes advantage of that fact that the freezing point of water is different to peroxide. The difference depends on the concentration of peroxide/water. Its interesting that for concentrations of bellow %62 the water will freeze whereas for higher concentrations the peroxide will freeze first. What is sometimes done is to sparge to around %65 then separate the peroxide by fractional freezing. 

I read a very interesting article on a patent that NASA own that uses a membrane filter with sparing.  A plan of this can be seen bellow.

The membrane (similar to a reverse ozmosis membrane) has a selectivity towards water (it prefers to only let water through) although because peroxide and water are similarly sized so it does let quite a bit thorough  (the articles says 2:1 water :peroxide is good)  The sparge gas then takes away the liquid that gets through the membrane. I do see a flaw in this method, or possibly I am missing something. Assuming that the membrane filter tubes have air in them (the sparge gas), some peroxide and water (more water than peroxide) but all liquid that gets through will be evaporated if the membrane tube is to not get filled up with liquid. If thats the case then I can't see what the point of the sparge gas is. You may as we'll just  use it like a typical reverse osmosis setup. Doing that you can turn %50 to %75 (2:1 selectivity). You can either throw away the waste of save it then repeat the process with it (25 to 37.5). 

I will probably just concentrate on sparging for the moment as it seems to be the easiest to get going. I have started designing a regenerative desiccant dryer, and I plan on using a aquarium air pump to pump the air for sparging. I should be able to get it decently concentrated just using normal air on a reasonable dry day.

I am becoming concerned about the safety aspects of using using peroxide. Sparging is quite a safe method but there is still the issue of safely handling it. Also it can become quite dangerous if contaminated with things that will burn. I don't plan on concentrating any significant amount until I get the new workshop sorted out, which should be over the next few weeks. I have ordered a full face shield (at the moment I am wearing enclosed protective goggles) and will probably order a safety shower for the new workshop. I am considering buying a protective PVC suit to wear but that may be overkill. Armadillo and lots of others regular handled %90 just take basic precautions of eye wear and pure cotton clothing. I would like to develop some strict guidelines which we will all use to handle the peroxide (no matter what concentration it is).

We are still planing to get the nitrous engine up and running, but we are just waiting for another opportunity to test. This will be in the first few weeks of the holidays.

Tuesday, 27 September 2011

Cancelled Test

We had been planing to conduct another test last weekend but unfortunately  it had to be cancelled the night before.

The source of the problem was that the new H-Bridge motor controller dent have the power to drive the valve motors. I hadn't tried it before then because I thought it would be a trivial task and a waste of time, but I learnt yet again that few things are simple. When buying the motor controller I noted at the motor's specs and noted that it retired 3A while moving. The motor controller could provide this, but I didn't take into consideration that it required allot more current to get moving. So If I hand started the motor it would work, but it couldn't start on its own.

I had been working really really hard last week to get everything finished and it is quite disappointing to have to cancel the test. We probably won't get another shot to test before the Christmas break, because I have exams coming up which I really need to concentrate on.

In the last 6 months I have learnt a really important lesson - things are usually harder than you think they are going to be - The entire reason I used actuated valves was so that I can vary the amount of fuel or oxidizer going into the engine. I think that to keep things simple I will replace the actuated valves with solenoids. Once I get the engine going they can be switched back.

Another example of how things were not as simple as I thought they were going to be is the relay back. Apparently (didn't  say it on their ebay page)  they wired active high. This means they are closed when they are open and open when they are off. If I used them like that it would mean that if the relays lost power everything would open (solenoids etc.) at the same time as the igniters ignited. Not the ideal situation. Ariel suggested I modify them, by removing a resistor and attaching the signal line to one side of the removed resistor which worked quite well.

So I guess I really need to make less assumptions and check everything!

On the valve front I would like to continue development of actuated valves as they will be extremely useful, but the current implementation is a bit haphazard. It will work for just opening/closing but I am not sure I will ever get the accuracy I want out of them without some major modifications. In the past I had thought that all the play had to do with the method used to attach the motor shaft to bearing plate. I have now realized that there is also quite allot of play in the reduction gearbox itself.

Originally I had considered using a large RC servo to actuate valves, but wasn't sure if they would have enough torque. After talking to someone the other day who told me about a 1/4 scale servo he had that nearly took his finger off and i thought... thats exactly what I need! (not the finger bit). I bought  cheap 1/4 scale servo, which I will test soon (once I get a torque wrench). It reckon it has 3.2Nm of torque, which might be enough to open a valve. If not there are two options. Get a better servo (the one I got was relatively inexpensive), or get a valve with less resistance. The valve I am using at the moment is good because its cheap and rated to high pressures but it has a few downsides. The torque required seems to vary greatly depending on the pretension on the ball and the pressure, so i might be able to reduce the torque required at a particular pressure. Alternatively I could get a valve with bearings. I would like to research the different types of valve available.

On another note I now have a engineering job which is keeping me busy. In someways having a job is good because I now have more money to put into rocketry, but the downside is I have less time to use the stuff I buy. I have so far avoided buying stuff I don't need and turning into one of those old men... but it is a struggle! At some stage I would like to purchase a CNC mill, but I really don't have any need for it at the moment (not to mention any place to put it). I have been considering moving into a dedicated workshop space for a while now and now that I have a income I am able to. Ariel and I are looking at something about 100m^2 which should provide plenty of room. We have inspected a few places in the inner suburbs, but they are all a bit pricey, so we will likely go a bit out of the city. Over the holidays I will be working full time so I just hope that I will have enough time to work on rocket stuff. I would also like to start building up a group of rocket enthusiasts to work on projects. There have been manny discussions about the best way to organize such a group.

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.

Saturday, 3 September 2011

yesterday Buren and I worked for most of yesterday and finished the improved actuated valves (minus two shaft couplers I have to lathe). I also tested the pressure transducers and found them to be simple to use. We then started on a few modifications to the plumbing including adding a manual vent to the ox side plumbing. I was hopping to have the electrical components I ordered by now but they should arrive next week and won't take long to install. I also made a start on rewiring the relay box by removing all the old relays and mounting and wiring the new motor controller.

Hopefully  the new motor controllers combined with the feedback will mean good control over valve position, but I suspect that it won't be good enough for precise throttle control (like the kind that would be needed on a hovering vehicle). A ball valve is needed because its quick to actuate, but I was thinking why not use a actuated needle valve and a ball valve in series. A needle valve is not quick enough to be used as the main valve (would take a few seconds to open) but they are much more accurate at setting flow rates, and once the engine is going thrust won't need to change any after than this anyway. Just one possible mod.

Friday, 2 September 2011

I am still waiting for some of the electronics parts to arrive so haven't been able to do much work on electronics.

I also ordered new Nitrogen and Compressed air bottles from supagas (as they were much cheaper than BOC ) for the next test. Looking through the price list I was trying to decide what size to get, and decided to go for the 9.5m^3 over the 3.5m^ as it was only $10. I didn't consider the size of the bottles, and the G bottle is a bit larger than I was expecting. I will probably have to lie to down in the trailer (horizontally) but having lots of extra gas means I will be able to throughly pressure test without worrying about running out of gas.

We also did a wireless test of the new WIFI control system and found it worked excellently at 200m with the routers default antenna.

Thought I would post a few photos of Buren has taken of the last month.

Sunday, 28 August 2011

Buren and I worked yesterday on fixing up the oxidizer tank mounting. I was thinking the other day about the run tanks and concluded that their no different from the tanks used by commercial hybrid rockets (as the tank is of course vented to reduce the pressure inside).We decided to just bolt the tank to the test stand as we were having difficulty with the steel round system.

We also removed the actuated valves and mounted the valve hardware to a much thicker piece of c section as the valves had a bit of flex at the last test. Also at the last test Buren broke off the head of one of the bolts holding the valve plates on so we had to drill out the remaining pieces of bolt. They came out easily so the hole didn't need re-tapping. I also made the mounting plate to hold the potentiometers (for feedback).

I am just waiting for the electronics to come then I can start on upgrading the electronics.

Unfortunately the next test will have to be delayed by a week because Ariel and Rob will be busy during the planed test day.

Thursday, 25 August 2011

So the long network was more problematic than I had initially though (in that it doesn't work). I took a spool of 200M of cat5e cable, crimped two ends and connected my computer to network and at first it looked good (flashing lights) but it would only stay connected for a a few seconds then would drop out. I tried forcing 10mbit and it would stay connected but i was unable to log into the router or ping any other computer. I thought of trying with cat6 but didn't really want to buy a box if i wasn't sure it was going to work. I guess I will have to use wifi if i want networking to the stand. I am going to try some range tests with wifi and see if I can get 300m range from a router wit default settings/antennas. If I can't i will have to go to directional antennas. I still think a wifi network will be more reliable than the xbee just because a nework has allot more redundancy built into it. 

The USB network server arrived the other day and works really well. I thought it might not work too well with a usb-serial chip but it worked first time which I was really happy about. The software is quite basic (which is good) and after installing it I was able to connect the FTDI chip on the Arduino to my computer and program over the network. Another feature I like is that different computers can connect to the usb device (only one per port) so we can have a few people monitoring the different webcams while I concentrate on the control program. 

I decided to go with proper motor controllers for the valve motors the other day (over relays) as it will allow me to have much more control over them. Previously i was only able to send about a 5ms pulse which was about 1/8th of a turn but with the controls i won't even need to pulse the valves as I will be able to vary their speed. Eventually i hope to have a control system using the feedback data to actuate the valves so all i will need to do is select a position and the valve will go to it. I ordered a nice 2A dual motor controller. The other advantage is everything will be much neater as I eliminate 4 relays and the controller is quite compact.

I have also been working on the safety operational plan. Writing it was quite a daunting task as it needs to cover allot but I started with some checklists and have been building from there.

We have also secured a slightly closer test site (1/2 hour drive). If all goes to plan I would like to have everything finished  by next weekend for a test the following saturday or sunday. Last time we were rushing to get everything finished and this time I would like to have a week to clear my head and double check everything is %100 operational.

Monday, 22 August 2011

The last week I have been busy catching up with uni work so I haven't had time to do any rocket stuff, but I have ordered all the parts I need with long lead times.

I decided to replace all the relays in the relay box with a nice neat relay bank as the transistors on the old ones are dead (not too difficult to replace, but i still haven't identified the cause) and don't want to rick the same problem. The new ones are optically isolated from the micro controller which is a nice feature. Also the igniter will be on a separate battery.

I have also decided (reluctantly) to ditch the wireless control scheme and go for wired. I really liked the wireless control system and haven't had any major issues with it, but it is not %100 reliable (does loose connection from time to time, although doesn't affect operation) and after the last test I have come to realize everything has to work %100 of the time (not %99) because if something can go wrong it will. Wireless does have its uses, but I think a cable is better for this application.

The new control scheme will use a 300m length of cat6 cable, through which I understand I should be able to maintain at least 100M/bit speeds. There will be a usb-network server on the test stand which the micro controller is plugged into and shared over the network to a computer. The other advantage of a cable is that I will have enough bandwidth to run streaming video from the stand. The usb server supports 4 devices so I plan on having one usb tilt-pan camera and another fixed webcam. This should give me a good view of whats going on with the stand. One concern I have is that the usb server won't work well with the Arduino, bit I have ordered one and will know soon. I can always use a computer on the test stand sharing usb, but would prefer not to. I had considered a more direct approach of using a arduino with a lan port, but I really didn't want to go into programing for that and although the hub adds one layer of abstraction (and source of failure) it will act as a serial link (same as the xbee) so I won't need to modify the control program at all. Also if the cable is struggling (which it shouldn't) I can uses booster.

Valve feedback is the other major thing that need implementing. After some discussion with ariel about the different options (trimpot, 12-way encoder and optical encoder) I deeded to go with a simple trimpot. I did find a nice 100 count encoder which was relatively cheap and would be more accurate but the problem is its not absolute and could need calibrating. I thought of implementing an auto calibration with two limit switches but why complicate something if you don't have to, and with a %5 trimpot i will have all the accuracy I can handle.

Also I need to add a manual vent valve to the nitrous side as after I lost control of the stand we had no way of venting other than manually turning the throttle valve. I was thinking of attaching a rope to the two manual vent valves so that in the event of a total loss of test stand control I can still manually vent from a safe distance. Again I could go for a complex redundant electronic backup system (that vents electronically) but why complicate things! Also I want to remake the valve hollers out of thicker aluminum C section, as I noticed some flex in the 3mm one.

Much work also needs to be done on the operations manual. I really want it to be something that is useful, not something that is done because it needs to be so I plan on compiling it over a few weeks so I can give it good thought.

I plan on working with Buren on sunday on the mechanical things, and we should be able to get most of them done. We are hopping to be ready for anther test in the next 2-3 weeks or so. I also need to buy a markee, table and chairs before the next test. I was tempted the other day to get a new generator (11KVA petrol for $1000!) of ebay, something I have wanted for a while but don't really have the need for at the moment Using all my power (pun intended) I managed to avoid becoming one of those people who buy tools not because they need them but because they want them (which is something that annoys me) With a surge protector (so it doesn't ruin my charger again) my 500W  one will be enough to power all our devices. Also  at the last test Marco suggested I have something fun I do before each test (the Russians used to pee on their rockets for luck). I have thought of a good pre-test ritual, although I am not sure everyone else will enjoy it as much as I will - hint - we have a somewhat different taste in music......

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.

Sunday, 7 August 2011

I was debating weather to bother with making the new tanks as its allot of effort, but i am very glad I did. Also I should mention that my friend Mitch came up with the threaded rod idea.... thanks Mitch! Buren and I spend yesterday and today making and mounting the new tank the the stand. When we opened the old one we found allot of congealed grease mixed with rust all over the orings and the end of the tank. It would have not ended well if we filled it with nitrous. The new tank actually didn't take long to make but mounting it to the test stand was quite a hassle as we couldn't get it secured well enough and it would always come loose. I am quite happy with how the tank came out, and it is completely severicable so in future we can just open it up to clean it instead of having to cut the pipe up to get the caps out.

We also started cleaning out the nitrous side lines with acetone but the tanks took one day longer than expected so we didn't get that finished. All that needs to be done before the test next sunday is finnish cleaning out the lines and sort out the valve timing (time required to throttle and fully open the valves).

Tuesday, 2 August 2011

Updated program

Did a bit of work on the control program tonight. A few of the buttons are not functional yet, but everything is how I would like it for the first test. Possibly will add in a display to show the approximate valve positions.

Monday, 1 August 2011

First test date set, odds and ends + new tank

I have been busy with the start of uni for the last week, but also have been talking to a few people about test sites and also some of the safety aspects to do with working with nitrous oxide.

We have found a location to conduct the first test, and set the date for the test as the 14th. Thanks to all the people who suggested test sites!

Things I need to do before the first test:

Make 10 igniters
Buy acetone and clean nitrous side lines
Dry lines
Modify plumbing for new pressurisation scheme
Make line from argon regulator to argon inlet
Flow test @ 500PSI - Check for leaks
make new tanks and install
Wire up argon solenoid
complete dry run
Clean relief valve with acetone
Set relief valves to 900PSI?

Following a discussions about nitrous oxide safety issues I am concerned about the traces of oil that might be in the main tanks. I have washed them out throughly, but There could still be oil trapped behind the o-rings and any oil would be really bad. The problem is that the current design does not allow for opening (have talked about this in detail before). I pressure test with oil, so i cant pressure test, then clean it internally. I have a new design which involves not bolting to the pipe, but using lengths of threaded rod running the length of the pipe to take the axial load. I have all parts required and if anything it should me much quicker than a regular tank because there are only 8 holes to drill (vs 12) and I don't have to thread the holes. One thing I am aware of is fracture induced by the thread in the rod, as it will introduce a large stress concentration. I have calculated this, and will also pressure test.

Add in pulse right forward + reverse buttons
Add in on for time buttons

The software is still rather basic, But it will do.

After I run the first test I will have a better Idea of what features i want in the control program. I have ideas for a automated sequence and other advanced features, but i want to do a basic test first to make sure everything works before I complicate it. One feature I will need to add before the test is button that moves both valves to low throttle and another for fully open. Also a close valve button wouldn't be a bad idea.

Also for the first test I won't have time to install the pressure transducers or have a working load cell amplifier but I am more concerned about other things at the moment.

A few things to do but I have till the 14th.

Saturday, 23 July 2011

Finished valves, nearly ready for a test

Today I finished up the last of the electrical work to get the valves connected. After that I played around with the timing to open and close them, and also trying to get them to reliably go to specific positions. Unfortunately the two valves are not the same (one is geared almost double) so they require different times to actuate. I made the key to couple the plate to the motor shaft out of soft aluminium so that if it tuned too far it wouldn't rip itself apart (the motor and gearbox has about 150Nm of torque). I broke a few keys at the start but didn't break any after I got better at the timing. I was worried that the minium time required for the relays that control the motors would be too big to get fine control of the valve position but it seems as if I can get at least a 100ms pulse. I am having this wired problem where the motor would rotate more in one direction that in the reverse, even though it was being pulsed for the same period of time, which I am yet to solve. There is a small amount of play in the position, which i think i should be able to at least improve by using a Steel key. Also something to improve would be putting limit switches on the motor, as i am worried about a key breaking during a test and having limited control. I will do a few dry runs and if its an issue I will have to add them. I am not really confident in the valves ability to hold its position after a few movements, after about 4 movements I would not want to rely on it being where it should be. For the first test I really only need three positions, closed, 1/10th for startup and full open so the accuracy won't be that big of an issue.

Also I have started thinking about the startup sequence, which felt odd at first because for the most part there has been little theory and a lot of time consuming fabrication. I plan on using a pyrotechnic igniter because its simple, reliable and I believe will limit the possibility of unburnt propellant collecting and causing a hard start. I have two ideas for igniters, a thermite based igniter and one based on a cylindrical strand of solid propellant. The thermite based one has the advantage that it is more energetic and will throw sparks increasing the chance of ignition. The solid propellant one although not as energetic and having a smaller burning area will increase the chamber pressure to (if sized correctly) operating pressure. I am worried that because of the large initial pressure differential and the inability of positing the valves with precision that the starting propellant flow will be too large. Pressurising the chamber will reduce the chance of a large volume of propellant entering the chamber causing a hard start. The igniter will need to burn for at least 5 seconds, but the longer the better. The other advantage of thermite is that its burn rate not really sensitive to pressure, whereas too much solid propellant could in itself cause a  hard start.

After the igniter has started burning and visual confirmation of the burning has been acknowleged I will open the fuel and oxidiser valves to 1/10th or thereabouts. Form what i have read its better to have a fuel rich flame so the fuel valve will be open more than the oxidiser one. Once I have visual confirmation of the propellant burning I will open the valves to full. Once the chamber pressure is right it shouldn't really matter how open the valves are. I am still not really sure I understand why the chamber pressure settles to a particular value, dependant on the feed pressure (as the flow through the injectors isn't choked) . Thats something I would like to understand better. Whenever I try to think about it I go in circles because the chamber pressure is dependant of the mass flow which is dependant on the chamber pressure. I understand that with a fixed exit area the pressure will reach an equilibrium but how would you possibly calculate that? More reading required.....

Anyway so I am pretty much ready to go for a first test. All I am waiting for now is a location. Next I will run some full duration tests with 750PSI and make a few igniters to test. Good igniters will be a evolutionary process as i can't really test them properly without a firing. I will try firing a igniter while flow testing with water to see how the flow rate changes but the water will probably mess with the igniter. One other think I need to do is drill a hole in the chamber for the pressure transducer. If i have enough time before a location is found I will start working on having electronic sensors which are transmitted via telemetry (which i will need to do before a second test anyway), otherwise a pressure gauge and a camera will have so do. Sensor data (in particular pressure) would be very useful for knowing whats going on in the chamber but its not necessary. For the first test all i really want to so is a few 5 second runs. Also here is a few pictures of various parts. Since taking the batteries out of the relay box I remounted everything and its a lot neater now. The cooling jacket is on the chamber (only one of the two barbs in currently on). You can see little bits of oring coming out, but it holds pressure and doesn't need to so I am not really worried. See if you can guess what the last picture is of.