Sunday, 29 May 2011

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.

Friday, 27 May 2011


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

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.

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.