Progress

The thing i had to do today took longer than expected. I had hoped to be home by 1 but i only got back at 4. I worked on the new chamber till 10:30. I bought a new center lathe lathe to replace my small hobby bench one about two months ago and this is the first solid work out it has gotten. There always comes a time when your dragged out of the "honeymoon" phase with a new bit of machinery and today i was definitely dragged. I had quite a few issues with it in particular centring with the 3 jaw chuck. In a 3 jaw chuck the jaws move together when you spin any one of three keys. I was finding the work would be off centre sometimes by a few millimetres. I spent at least an hour trying to figure out what the problem was. The chuck itself was true so i knew nothing major was wrong but nothing seemed to make it better. Turns out that you have to tighten each key incrementally bit by bit, which makes no sense as they are all connected and turn together, but i think it would get jamed slightly when tightening. I have to say for the price i am not entirely happy with the quality of the lathe, and I  wont be buying any chinese machinery soon. Stil its a major improvement over the previous lathe, which was really too small for the size work i was doing.

Anyway so i got the new chamber nearly finished. All I need to do is cut the o-ring groves and dill and tap the threads to hold on the cooling jacket and injector assembly which will only take an an hour or so. I didn't bother putting in the groves and channels in  as they don't really do that much accept from look cool and there is more than enough cooling surface as it is. For the last couple of days I have felt anxious over the amount of work that needs to be done, finishing the chamber made me feel a bit more confident. The new chamber is identical to the old design but it has a big extra flange at the top for the injector to bolt on to. I didn't feel particularly confident with the last design as there is a lot of force on the injector and previously there was only 10mm of thread which i was afraid was going to shear. Unfortunately i couldn't get the broken drill bit out of the chamber i made last night so I had to start again. This one is much more centred also.

I am a bit worried about the extra flange melting as it is away from the cooling jacket. It also makes the chamber 3cm's longer. It will be near the injector so it shouldn't get too hot. Also i realised today after looking at another design that the oxidiser injector is on the outside. In most designs i have seen the fuel injectors are on the outside to film cool the wall. I am not so worried about cooling as the oxidiser oxidising the chamber wall. Space was really the drive to placement of injectors. There is one fuel and five oxidiser injectors. Since i am using spray injectors of the same size there isnt really a good way of  positioning them so the fiel is on the outsice without using diferernt sizes. I am already using close to the smallest spray injector i can find. So i guess i will keep the design as it is. I might do some more research into the issue.

I also ordered the type 30 fitting for the nitrous bottle, and it should be here tomorrow. For the next two days I will be away so i am not expecting to get a huge amount done but I will ahve a play with the xbees and try to get some of the test stand software done. I am having some troubles with python where it will freeze when i paste any code in to idle. It can pen and run saved code fine but pasting makes it freeze. Its really quite odd, i have found a few people talking about the problem and i think its a bug. I am just not sure how to uninstall/downgrade it (on a mac).

27th June

I didn't get nearly as much done today as I would have liked. This morning I went and bought some stock aluminium round and a parting blade holder. Alot of the day was taken up with taking a friend to the airport and a engineers Australia presentation this evening. I started to make another combustion chamber this evening but I managed to get a drill bit broken off inside the workpiece ruining the last two hours of work. I might try to salvage it tomorrow but it seems like its slightly eccentric and doesn't spin true.

I changed the design of the combustion chamber to include a flange where the injector bolts to the engine. previously there were only a few cm's of material where the thread of the bolt met the chamber, which I was worried about failing. I cant really be bothered to explain more but I will show a comparison of the old and new chambers when its done. I have some other stuff to do tomorrow morning but i am hoping to have the second chamber finished tomorrow. I am going away for a few days on the 29th and 30th coming back the 1st so am hoping to write some of the test stand software while i cant do any building.

I managed to track down and identify the fitting on the nitrous bottle. Its a type 30 fitting which is an australian standard fitting. The whole australian system for fittings is quite silly as it seems to be a zoo of America and British threads and sizes. I will call gascon systems to get an adapter to 1/4" BSP tomorrow. The wireless parts also came today and I might try getting them going when I go away.

Start of holidays, and a what i have been up to (or lack of)

I finished my last exam on friday, and am quite happy to be holidays and working on rocket stuff again. I completely stopped building anything over the exam period as I have difficulty balancing building stuff and study. I am getting better balancing my time, and i can work fairly well on both during the semester but I have difficulty

I have decided to postpone any peroxide work at the moment so I can concentrate on building the nitrous demonstration engine. My chemist postgrad friend has gone overseas also so he isn't able to help for a while also. I still really want to develop some peroxide stuff, but i get the feeling that its just a distraction and at the moment i really just need to get something going. On the peroxide note I do have a possible source for silver mesh : Art stores. I was in one the other day and they sold copper mesh. I asked the manager if they had any silver mesh and she said she thought they used to but dident sell it anymore. She got my details and said she would look into it for me (probably wont hear from her) especially after i told her what i was using it for but I might try calling some other stores if i have time. Also it might not be real silver, but just something that looks like it.


I spend most of today cleaning up the workshop and the office as everything had gotten a bit messy over exam period. I also got the chance to try out a new toy i ordered before exams but hadn't gotten a chance to try. I have always wanted a plasma cutter but could never really justify the cost. Well lately I have been making lots of parts made from plate steel and aluminium and cutting them from the metal band saw is very slow and a bit dangerous. For thick plates you need to apply allot of force towards the blade, and slipping means your fingers go into the blade with a lot of force (that hasn't happened to me). So i figured i would treat myself. Its a chinese knock off of an italian model (from ebay) but seems to to work quite well. Its 50A and apparently it can cut up to 16mm of steel, although at about 45A it trips the circuit breaker in my house so i haven't been able to test it.

I have also decided to ditch the usb-lan cable in favour of a wireless xbee (serial wireless module) I have ordered a 60mW pair which are quite easy to program with ardwino. I am slightly concerned about the safety aspects of using a wireless module to control the test stand, but with a wired cable to control arming/emergency stop  it should be fine. The module says it can go 1600m. There is also a 1W variant for only $180 each which would work very nicely for telemetry on a flight vehicle. I remember reading that Paul from unreasonable rocket used a 100mw xbee at 900mhz (instead of the 433mhz i have) for telemetry on his helicopter.

I would like to be ready for a test in two weeks (10th). There is quite a bit of work to be done, but I am looking forward to the challenge.

Peroxide ideas

I have had a few ideas for peroxide.

Firstly having read allot of posts by armidillo and unreasonable rocket, I have concluded that peroxide is not the holly grail i was wanting. Nothing ever is, and i was silly to think so but i was hoping that peroxide would be significantly easier than Nitrous. The problem i can see is that everyone using a catlyist bed ends up spending a significant portion of their time researching and testing them. 

If i was going to go down the catalyst pack route i would probably go with 90% peroxide and a silver mesh catalyst, as this seems to be the best combination of performance and ease of use. Problem is i cant really find any silver mesh so i would probably make my own. I had an idea to use activated silver pellets which are used in the production of formaldehyde, but i have no idea if it would work, and the minim order quantities are large. I suspect the pellets might be too delicate, as they are not really designed to withstand mechanical wear. I might be able to get some as a sample, but only once. For plating mesh myself, silver cyanide is needed which is quite toxic and i have no intention of handling any. It might be possible to get a company to do it locally, but I will need to experiment a bit to get the mesh right, and I cant see any company being happy about this. The whole catalyst business is allot of messing around and i would prefer something i know works even if its slightly more complicated.

What seems the most promising now is a bi-propellant %90 peroxide-hydrocarbon engine either ignited conventionally with a pyro igniter or with potassium permanganate dissolved in the fuel to catalyse and start ignition. I have no need for a restartable engine, but the second method would have manny advantages including reduced risk of hard starts. Anywhoo, i could always start with the first and move to the second later.

For the current nitrous all the valves and other bits i ordered from flow-fit online (uk hydraulics supplier) finally arrived on monday. It was about a month and a half since i ordered it and i was not happy with how long it took them. I think they forgot my order. I emailed them several times with no response. They only contacted me after i started a paypal dispute. I am glad i paid with paypal! They are quite cheap, but if anyone is considering using them i would recommend steering clear. Also I will need to degrease all the fittings as they come with mystery grease I assume is oil based.

I am still trying to find a reliable test for oil in my tanks and fittings, which i can use prior to filling with nitrous. Nitrous can form shock sensitive explosives when combined with hydrocarbons, and that was one of the factors contributing to the scaled composites disaster.

Also some cheap pressure transducers i ordered from ebay arrived yesterday. They were quite cheap ($40 inc chipping) and i am a bit sceptical they will work as advertised. Even if they are not particularly reliable i really only need a rough pressure measurement so they will do. If i cant get them working i probably wont have time to order more so I guess it will be gauges and a camera.

I am still fighting the urge to work on rocketry stuff as I really need to study for exams. On the 24 when everyone is going out after the last exam, there is know where else i want to be but in the workshop!

Also eventually I would like to try out two variations on my nitrous engine:

1. Run in monopropellant mode after engine gets warm
2. Run with peroxide.

USB extension

For the test stand I am planing on using an ardwino to both control and log data from the rocket and associated equipment. I am planing on having it connected to a computer via USB where it will communicate with a "dashboard". By dashboard i just mean a simple display with some buttons to control and displays about whats happening. I want to be be a while away from the stand so i will need some sort of extension. I have thought of using something wireless possibly using packet radio, but I decided to keep things simple and use a RJ45 usb extension. their quite cheap ($10 from ebay) so i am not sure how well they will work, or how far they will go. From what i have read they can go 45m but bandwidth is verry limited. All i am sending is some serial information so i am hoping it will go at least this far.


I also need to incorporate some safety systems. I think this can be as simple as a physical arming switch which connects the pressurisation solenoid and igniter to the power supply.

Also while talking about the igniter I plan on using a simple bridge wire covered in a slow burning smoke mixture. For the power supply, for some solids in the past I have simply used two rather large 12V batteries in series but if i have time i would like to make something slightly more sophisticated, maybe a capacitor discharge circuit, or spark generator (attached to the bridge wire) from a single cylinder engine. The later will have issues with EMF but since it will be only on for a second before the test it shouldn't matter.

In the peroxide department i have enlisted the help of a chemistry post grad who will hopefully be able to help me with HTP production. We should be meeting next week to discuss methods etc.

Also in the impractical business ideas department..... Selling regenerative desiccant air dryers! One of those things that are way overpriced for what they are because they are a highly specialised item.

Peroxide

For an ammeter making a liquid rocket engine you really only have three choices of oxidiser. Those are Nitrous oxide, Peroxide and Liquid oxygen.

Peroxide is probably my favourite storable propellant. Granted I haven't actually used any liquid propellants yet, but if I had I am sure peroxide would be my favourite. As a starting point it doesn't cause cancer. Liquid oxygen would be lovely and although the performance is higher so is the cost. The actual cost of the propellant is quite cheap (don't have any figures for how much it would cost in Australia, but in america its about .1-3$/kg depending on the quantity you are after) I haven't tried to get any, but I can imagine it would be a mountain of paperwork and explanations. Anywhoo I am getting a tad carried away, I could write for a long time about advantages and disadvantages of propellants but what i really wanted to talk about was methods of concentrating peroxide.

Methods are:
Freezing and separating water ice from peroxide (ice freezes 0.4k higher)
Vacuum distilling
Sparging.

I wont go into great detail about the first two but quickly freezing would work theoretically but will be too tricky to implement. Vacuum distillation would be ideal, but the equipment will be too costly.

Sparging will be very slow, but relatively safe
Sparging involves bubbling dry air through the peroxide. As the vapour pressure of the water in the peroxide solution is higher it will evaporate at a higher rate than peroxide. Although you will loose some peroxide, but will be 1/10 that of water.

The peroxide also needs to be filtered as it has stabilisers in it, which will foul catalysts. This can be done using a ion exchange resin.

The tricky part I see is getting a source of very dry air. A method I immediately thought of was using silica gel. This is how most equipment that needs a small source of dry air gets it. The problem is air has a alot of water, and sparging needs a a lot of air. The solution is a regenerative desiccant dryer. Its basically two vessels with desiccant. Only one is used to dry air, while the other one regenerates. This is done by simply done by heating up the desiccant so the water evaporates out. A controller monitors the humidity of the output air and switches, and regenerates automatically. I am looking at making one of these now. I will also need a source of oil free air (cant use a compressor). I wouldent imagine the head loss through the dryer would be too high, peobally in the order of 2-10PSI. A car turbo would work well. More about this later.

Things to do before test

Thought I would make a list of all the things that need to be done, and parts that need to be ordered before the first test firing of our 100N nitrous oxide-ethanol test engine is conducted.

Motor:
New injector needs to be lathed.
M3 holes need to be tapped in motor
O - ring groves on aluminium chamber need to be finished.
Spare Steel motor need to be lathed - Incase the aluminium one melts
Igniters x lots

Test Stand:
Mount load cell to adapter
Mount manual ball valves
Mount relief valve
Mount regulator + argon tank
Plumb all components together
Pressure test
Cold flow test with dry-ice -> liquid CO2

Automatic Valves:
Make coupling frame
make plate with square + round holes
Calibrate valves

Monitoring + Control:
Test pressure transducer
Tap pressure transducers into chamber
Fabricate box for controller
Code control dashboard


To Buy:
New 0.6mm brass injectors - IFS
Square key stock
Solenoid's for motor control
SLA battery for control system - From chris?
Adapter: Nitrous tank AN10? - 1/4" BSP
1/4" flexible hose oxygen safe - Male-Male
USB extension adapter

All up I estimate this will take 1.5-2 weeks working 9-5. There is quite a lot to do, but I have nearly all of the parts already or on order so there shouldn't I waiting for anything. Also my new lathe has speeded up lathing quite a bit. My last exam is on the 24th of june, so after then I am planing on working pretty much continuously. Hopefully we will be ready to conduct a test in the third week of the holidays. I would also like to use some of my holiday time to another project, which I wont discuss now.

As for the test site, its still not clear where we are going to conduct the test. There is talk of using a location at pinjara hills, but its not certain yet. I have a few friends who have farms etc which we could use but they will be at least a two hour drive.