FTC Payload

I've been quite busy this last week with non-rocket related things but have continued the steady progress on the FTC payload section in my spare time.

All the components are now fitted inside the payload section, but more work is still needed to secure things a bit better for the expected G forces of around 70G. The entire payload section shown above currently weighs 118 grams and includes the complete deployment system with servo motor, parachute, flight computer, altimeter and batteries. The flight computer is V1.5 on a 25mm wide PCB to fit into the T-8 tube.

The complete deployment system is only made from items found around the house. The full details will be given in the next main website update along with a video of how it works.

We will be picking up some kevlar line for the parachute on Saturday which should make things a little lighter and stronger.

It's been fun trying to fit everything into such a small space. For deploying the same size parachute as we have been using on our smaller rockets the entire deployment system is about 25% lighter than our existing ones and has a lot less drag.

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FTC rocket update

Over the past couple of days we have been putting a bit of effort into getting the FTC rocket ready for its first flight. I did a test to see if the fins can be glued directly to the reinforced FTC body, but PL premium does not hold well to the the glass strapping tape. They will have to be attached a different way.

The parachute ejection system is not complete yet, but is working quite well. We can use a fairly large parachute in it.

I've started soldering together V1.5 of the flight computer in a format that fits into a T8 tube. There will be one small RC servo motor for deployment. The payload section will also include one of the altimeters. Other than that, the pressure chamber is finished.

Pictures will be posted when more of it is assembled.
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Thrust Data Available

We have spent all week collating the data from the thrust tests. Our main website has now been updated with the results here:

http://www.AirCommandRockets.com/day68.htm

There were some interesting results and we want to do further follow up experiments, as well as some new ones.


It's a bit of a long write up so feel free to skip the boring sections.
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17 Tests in 3.5 hours

Today was a good day for testing. We went through quite a bit of air out of the scuba tanks, but the tests went relatively quickly and we got through most of what we wanted to get done.


We are in the process of analyzing the results at the moment and putting together a video of the tests as well. It will take a few days to write up the results.

Some of the tests included:

• Robinson coupling choking and blow through effect,
• Jet foaming techinque with and without foam,
• Reduced mixing chamber for jet foaming,
• Some tests were done with a 9mm nozzle and some with a 7mm nozzle,
• Foaming agent concentration difference
  
• We tested 2L of carbonated drink in the rocket,

After we analyze these we will have a better idea about what things we want to redesign and test further. The next set of tests will include the variable nozzle with different holes and with and without foam.

FTC Rocket

We have also done some more work on our FTC rocket. We have the fins cut out now, but more importantly come up with the way we want to do parachute deployment in a T-8 FTC tube where there isn't a whole lot of room. The best part is that all the components are common items that can be found around the house.

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Software

After importing a lot of thrust data from the test stand into Excel it quickly became obvious that the data still needed a lot of processing before it was useful. While it is easy to do in Excel, it is quite tedious, as the data has to be trimmed, aligned in time, averaged, calibration scaling applied, total impulse calculated and then graphed. This was taking perhaps 10 minutes per data set so I decided to extend the functionality of the WDQ to CSV exporter application I wrote a few weeks ago.


The application now can do all of the above tasks. With a few mouse clicks I can get total impulse, average thrust, thrust duration etc. This allows us to quickly review the data during testing and alter our tests based on the observed data. This should help in the design process as we make changes to the design we can get instant feedback on the design.

The full software functionality will be covered in the day68 update with the calibrated test results.

We are hoping to do a full set of tests this long weekend.
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Calibrated Testing

This weekend we performed a number of calibrated tests on the test stand. We first measured the load cell's linear response by suspending successively heavier weights on the load cell, and then flipping the test stand over and applying the same weights again so that force was applied in the other direction. The load cell responded very well.

The first test was an attempt to measure the power loss due to the blow through effect in a rocket with Robinson couplings. The test results from the three identical firings were very good as the thrust curves were in very close agreement with each other. That gives us confidence on the repeatability of the experiments.

When we were testing the rocket without the couplings we had a small problem where the thrust curve just exceeded the gain setting and as a result the top of the curve was clipped. We will re-run this again but with a lower gain setting. We try to keep the gain as high as possible in order to get maximum resolution.

Full details of the tests and data analysis will be put on the main site in due time. We will rerun the non-coupling tests before publishing the results.

There were a couple of minor issues we had to resolve with the test stand initially such as the little locking tabs in the gardena release mechanism flying out during release. But once fixed the tests were quite quick.

Because we had the test stand and equipment setup on Saturday we didn't go launching any water rocket with NSWRA, although I went over with the kids to watch other people's pyro rockets. It was nice for a change not to have to go and spend a couple of hours setting and packing up, and I got to enjoy other people's rockets and actually had time to talk to them. I've put together a highlights video from the day up to about lunch time here:

http://au.youtube.com/watch?v=4PPcZH3pK0Q


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Test Stand Details

We've put the details of the test stand on our main website here:

http://www.AirCommandRockets.com/day67.htm

It includes a couple of thrust curves.

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Test Stand First Firing

We ran our first couple of thrust tests on the new test stand. The tests were uncalibrated as we wanted to see what the overall performance was and if the gain on the amplifier is set correctly for the range of thrusts we will start testing with. Overall everything went really well and I am looking forward to doing the actual tests.

There are still a number of small modifications we need to do like automating the release of the nozzle and adding a non-return valve to it. We also still need to try PK's suggestion with a couple of resistors to eliminate noise a bit more.

I'm hoping we will get to do some calibrated firings this weekend with exactly measured pressure and water volume. We will suspend known weights from the setup so we can get reference values to measure the actual thrust.

Overall setup. The stand is normally firmly attached to one of the house pilons, and the table is well away from the splashing water.


The large spike at the start of the thrust curve is mainly due to me pulling the release head off the nozzle by hand. This should be smaller when automated where it falls away freely.



Full details of the test stand and first tests should be published on our website early next week.
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Test stand work

It's been a fairly quiet week as we have had a number of non-rocket related engagements. This weekend I continued work on the test stand. The test stand now has the basic frame and the load cell and load cell amplifier attached. The load cell to rocket coupling is also almost finished. We still need to support the rocket under test to stop it moving from side to side, but that will be done over the next day or so. We are quite keen to try the test stand and we will likely do a few test runs this week.

My mum has also started helping out in preparing the bottles and sleeves for splicing. This has drastically reduced the amount of time it takes to splice bottles together. I was able to do 4 splices in less than an hour.

I'm also in the process of writing up the full details of the test stand, but those will only be published after we have fired the rockets a few times so we can also report on the repeatability and accuracy of the setup.

If people have suggestions for tests they would like to see results for please let us know in the comments section below.

Some of the thrust tests we have planned are:
(each test is likely to be run 3-5 times to eliminate variance in water and pressure levels)

• 9mm nozzle with water only
• 7 mm nozzle with water only
• 5 mm nozzle with water only
  
• 9mm nozzle with Jet foaming
• 7mm nozzle with Jet foaming
• 5mm nozzle with Jet foaming
  
• 9mm CD nozzle
• 7mm CD nozzle
• 15mm nozzle with water only
• A look at the chocking effect of Robinson coupled bottles vs full bore tornado couplings.
• Variable nozzle performance with water
• Variable nozzle performance with foam
• Different foam generating techniques
• Comparison of different foaming agents
• Comparison of foaming agent concentration
• Test differences in the convergent section of the nozzle
  

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Multi-stage rocket

We flew our new two stage rocket with drop away boosters last Saturday. While things didn't go exactly according to plan, we still learned a lot from the two flights.

The full update is available here along with photos and video:

http://www.AirCommandRockets.com/day66.htm


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Improved Sensitivity and New Rocket

This week I spent a day rewiring the load cell and amplifier after one of the guys (PK) on the Australian Rocketry forum made some good suggestions about how to reduce the signal noise. I placed the load cell amp close to the load cell and enclosed the whole thing in a metal box. I also used coax cable to run the long lead to the DataQ logger. The noise level dropped off dramatically. It is now down to around 0.02V over the -9V to 9V range.


On the 70Kg load cell that allowed me to resolve down to ~5 grams = a sheet of A4 paper. (Yes I actually put a folded sheet of paper on it). This means we can get thrust measurement accuracy down to about 0.05 Newtons. This hopefully should be good enough to observe the subtle changes to components under test.

I'm very happy with the setup now. All we have to do is build the stand. The stand is a little more complex because it is going to be put on a pivot to allow us to flip it upside down and fill the rocket with water. I'll have to wait with this until next week as we have to get our rockets ready for the August 30th launch day.

Big thanks also goes to Tarp, astro and patch and others who helped me get the right parts and steer me in the right direction.

New Rocket - 2 Stage with drop away boosters

We have decided to combine a couple of our existing rockets to make up a bigger rocket to launch on Saturday. We are taking the two stage rocket launched last time and adding another 2L bottle to the bottom of it. This actually came from Polaron VI launched a couple of months ago and includes the booster retention tubes. We will attempt to launch the rocket using the Gluon II boosters.

This will be our most complex rocket to date, and because of that I am not sure how successful we'll be in getting it off the ground. But it will sure be fun to try. A brief outline of the rocket configuration:

Sustainer: (Tachyon V) 3.35L capacity using 1300mL of water + foam, 9mm nozzle. It is fitted with our V1.5 flight computer for deployment, has a FlycamOne2, a z-Log altimeter and a single parachute.

Main Stage: (Baryon III) 9.2L capacity using about 3 L of water + foam, with a 9mm nozzle. The sustainer is released by the Mk2 stager, and the single parachute is deployed upon release of the second stage using the piano hinge principle.

Boosters: (Gluon II) Attached to the mains stage are three boosters, each with a 3.35L capacity using about 1.25L of water each. Each has a 13mm nozzle and is equipped with a piano hinge parachute deploy mechanism that releases the parachute as soon as the booster separates from the main stage.

I haven't measured it but it stands about 2.5m tall. Will post details of rocket and if a flight is successful with the next update.

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Test stand update

On Friday I received the the load-cell so I was keen to get it hooked up since now I had all the components. It took most of Saturday to get everything designed and soldered up, and today I powered it up and ran some tests.

The current setup with the load cell amplifier, batteries and data logger housed in the box.

I was able to easily measure loads as low as 20 grams on the 70Kg load-cell. Initially I had some issues with noise being picked up by the wiring, and was able to reduce that about 10 fold with appropriate shielding and grounding things. Later, on the Australian rocketry forum one of the guys suggested how to even further improve the noise margin with cabling and locating the amplifier close to the load cell in a metal box. So the next step is to try that. Luckily I have all the necessary components, but will buy a new diecast aluminium box tomorrow and fit the amplifier in that.

The more accurate the setup is, the more accurately we can determine what effects design changes have on the rocket. With the above setup we can resolve ~0.2Newtons of thrust over the typical test range of about 30N to 150N. That range applies for our typical rockets with pressures of around 120psi with nozzles under 10mm. The same setup will also be used for full bore tests of up to around 600N.

I'm pretty happy with the sensitivity of the setup as is and would be great for most of the tests, but hopefully with the improved cabling and shielding we should be able to achieve higher resolution. I'll post an update when we test that.

I mounted the load cell for the time being to a big chunk of steel which will be eventually mounted on the test stand.
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New test stand work

We have been working on a side project for the past couple of weeks. We are keen to build a new thrust measuring test stand for testing design changes, but doing it the old way of recording a kitchen scale on video and then manually transferring the data into a spreadsheet just wasn't going to cut it for accuracy, and especially for making multiple runs.

We are doing it properly this time with an electronic data logger and a load cell hooked up to the laptop. The main problem with trying to do it the proper way is the higher cost involved as the equipment typically isn't your regular mass produced consumer electronics. The guys on the Australian Rocketry forum were a great help in recommending which equipment to use, things to look out for, and generally how to set it up. The data-logger we chose was from DATAQ. They have a number of different loggers with different capabilities at a very reasonable prices. I was very impressed with the delivery time from the time that I ordered. I placed my order just before lunch time on Thursday with the Australian distributor, and the package from Melbourne was waiting for me on Friday when I got home from work.

The load cells also tend to be quite expensive - easily upwards of $150-200+. We had been researching a lot of different companies and finally found a new 70kg load cell from a Chinese manufacturer whose cost and delivery were far cheaper than local distributors. It is still likely to be about 10 days before it arrives. I don't know what the quality is like yet, but I believe it should be great for our purposes.

The data-logger and load cell aren't enough though, and we also need a load cell amplifier as the datalogger only reads in the -10V to 10V range. The load cell only produces miliVolts over the entire deflection range which is too low for the datalogger to get enough resolution. The amplifier basically converts these small voltage changes to a voltage range usable by the logger. It also provides the necessary excitation voltage for the load cell. Again you can buy these off-the-shelf but you will pay upwards of $100+. Being on a limited budget, we decided to build our own load cell amplifier instead, which is based on an instrument amplifier IC. The circuit is relatively straight forward and these IC's are designed for exactly this task. The IC has been ordered and is on its way from the US.

I'll publish the full details of the entire setup and suppliers when it's calibrated and working properly.

The data logger came with free "lite" software for capturing and viewing the data. However, being free there are some limitations in terms of exporting the data and maximum allowed sample rate. The max sample rate is 240Hz which is more than ample for us. The full software with higher allowed sample rates is another $200. You can also buy a $99 software add-on that lets you save the captured data into Excel friendly format. (doh)

The free software, however, does record the data into their own proprietary binary file format. I recorded a number of waveforms today, and looked at the data in a hex editor. I noticed that it was not encrypted, so it was relatively easy to reverse-engineer its format and write a small program that allows me convert their format into a text .csv file format that is directly readable by Excel. (saved $99 there :) )

The entire thrust measuring test stand + software should cost us under $300 when finished.

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Baryon II and Variable Nozzle

We have finished doing the flight log update for the last launch day at Doonside. The primary goal for us was to test the Mk2 staging mechanism with a bigger booster and sustainer.


Details of the new booster and sustainer are also included in the update.

http://www.AirCommandRockets.com/day65.htm

We have also been working on a technique to expel extra foam from the rocket in flight and came across a way to make a simple variable diameter nozzle. The details of the concept and a video of how it works is included in the above update.


There is lots of testing that needs to be done on the nozzle, and different materials to try so it looks like we might need to set up our old test stand again.

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Thermal Testing

We have finished writing up results of the initial thermal tests. We will be adding to this post as we do further testing over the coming months.

http://www.AirCommandRockets.com/day64.htm

I am in the process of completing the flight log update from Doonside last week. Hopefull that will get finished in the next few days.

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Mk2 Stager with bigger booster and sustainer

This weekend we flew the Mk2. Stager with a bigger booster and a bigger sustainer to see how it performs under greater loads and higher pressure. The Baryon II booster has a 7.2L capacity, 15mm nozzle and launches with 2.8L of water. The 3.35L Tachyon V sustainer uses a 9mm nozzle and 1300ml of water/foam mix. We flew both at 120psi.


It was a good flight, but the high wind conditions on the day caused the rocket to fly in an arc rather than straight up and as a result did not reach the expected altitude. Staging happened as expected and both parachutes on the booster and sustainer opened as expected.


We are currently putting together a flight log update, although it will be perhaps a week before it is posted, as we are also in the process of completing the write-up of the thermal experiments we did last week. There wasn't enough time to post the thermal results last week as most of our spare time was taken up building the new booster and sustainer. Sometimes you have to find the balance between sitting at the computer typing and actually building hardware.

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Testing, testing and more testing

With the NSWRA launch day being postponed this weekend due to unfavorable weather conditions, we spent more time in the workshop testing all sorts of things and building a new two stage rocket that will use the Mk2 Stager.

First we pressure tested the new 3.35L sustainer to 120psi. It is using a new bottle we have not used before so we were curious to see how well it would hold up. Then we pressure tested the reinforced FTC to 180 psi. 180 psi will be the first launch pressure of this rocket. This is the actual FTC pressure vessel we will be using for our first FTC flights. The nozzle and end-cap are already attached and the entire length of the FTC has a single wrap of glass strapping tape.

After some recent great discussions on the Yahoo water rocket forum, about thermal properties of bottles, we spent some time doing thermal tests on how warm the air gets inside a rocket during pressurisation. This is important as high temperatures can weaken a bottle. The glass transition temperature for PET depends on a number of factors but can be as low as 69 degrees C.
Wikipedia lists this temperature as 75C.

"The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. "

We are in the process of collating the information and we will try to publish it sometime this week.

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Repairs and painting

After the CATO of the reinforced rocket (Tachyon IV) at Doonside, I have rebuilt a new reinforced bottle and pressure tested the entire rocket last night to 170psi. There were no visible stress marks on it so should be good to go for this Saturday.

I am also replacing the fin section on this rocket with 3mm plywood fins directly glued to the bottle. I coated the fins with 5 minute epoxy to add a little strength and water proofing. They will be sanded and painted tonight.

At the last Doonside launch event a couple of the members suggested trying vinyl paint for the rockets. I bought some white vinyl and plastic spray paint at SuperCheap Autos, but at $15 a can that is not all that cheap. I tried the paint on a PET bottle a couple of days ago. I lightly sanded half of the bottle with very fine sand paper and left the other part untouched. After a few goes I realised that you have to spray in multiple thin coats to get good coverage without runs. The paint dried within minutes.

The paint is a little flexible so bending and squeezing the bottle had no effect on it flaking off, like we have had with other paints. The paint on the unsanded side, however, did come off very easily when scratched with a finger nail. It was a different matter on the sanded side though. The paint held very well even when scratched. I'm keen to see how well it holds up in the sun with heat and UV.

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Mk2. Staging Mechanism Details

We have posted the launch report on our website from the latest Mk2 Stager test flights. We have also included the full details of how the staging mechanism works.

The launch report is available here:

http://www.AirCommandRockets.com/day63.htm

The stager details are available here:

http://www.AirCommandRockets.com/howitworks_2.htm


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Mk2. Stager Test flights

On Sunday afternoon we finally made it to the local park to test fly the Mk2 Stager, with a small booster and sustainer.

It was a good day of test flights. The first launch was good with good staging. We had a failure on the second launch with no release, but no damage was done to the staging mechanism. We made a couple of minor adjustments and then the final two flights of the day went well again. We had to leave the oval after flight #4 as it was getting too dark to shoot good video.

From simulations and the observed flight times which were relatively close to the simulated predictions the sustainer reached over the 100m (330') mark. Not bad for a little 600ml bottle with 200ml of water at 110psi.

This is a couple of frames taken from ground video of the staging taking place. The sustainer arced over a little probably because its stability is marginal mostly due to its short length. Seen here staging is happening around the 10-15m mark.

We will post the full results of the test launches in the next few days with photos and video. Soon after that we will also do the full write up of the mechanism itself.

The next test flights of stager will likely be on a medium sized booster and a bigger sustainer. We haven't settled on the configuration yet as we were waiting to see how these tests would go. The bigger booster and sustainer will have to be flown at Doonside.

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