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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Drop Away Boosters Explained

This week we've updated the main site with the theory and an explanation of how the drop away boosters work on the Polaron rocket.

http://www.AirCommandRockets.com/howitworks_1.htm



Other than that only small amount of work has been done on actual hardware due to other commitments. The weather looks a little windy for this weekend, but hopefully it will settle down on launch day.
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Booster and sustainer work for stager test

The booster is now complete for the flight test of the Mk2 stager. The sustainer needs a little more tape, and a coat of paint on the fins and it too is ready to go.



The booster is only a 2.1L spliced pair, and the sustainer is only 600mL. We built both of them small so we could test the stager at the local park. For this test we weren't all too concerned with aerodynamic efficiency. The booster uses the same parachute deployment technique that the drop away boosters use on the Polaron rocket. The parachute is behind a flap held by a wire. The other end of the wire is attached to the sustainer and as soon as the sustainer is released, it pulls the wire and deploys the parachute on the booster.

The sustainer does not have a recovery system. It just has a soft nosecone to protect it (somewhat) on landing.

We don't expect this combination to go very high, and we still need to run simulations to see what to expect. If the weather is good this weekend we will launch it.

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15mm Nozzles

We had a good weekend launching rockets despite a couple of CATOs. We launched the Axion rocket with a 15mm nozzle and a long launch tube which gives the rocket a nice kick on take-off.

The full update is available here:

http://www.AirCommandRockets.com/day62.htm

The update also includes a video of some static fire tests of the Mk2 stager we have been working on. We are keen to fly it as soon as we finish the little booster and sustainer. We will be able to test it locally without having to wait until the next launch day at Doonside.

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Side Deployment Construction Tutorial

Construction details of how we make our side deployment mechanisms are available here:

http://www.AirCommandRockets.com/construction_3.htm#SideDeployment

We have been using this technique on our rockets for more than a year now. But finally got around to documenting it. All the materials used are readily available and it can be adapted to things like Tomy timers and the like.



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First trials of new staging mechanism

Over the last few months we have been slowly working on a new staging mechanism. On Sunday we spent some time completing it and running through some initial trials. We test fired it 3 times, at 60psi, 100psi and 120psi. We did the tests just in the back yard with only bottles connected rather than real rockets. We were pretty happy with the performance after a few adjustments.



Next we are going to build a very small second stage (~600mL), and a small booster - likely to be just a spliced pair of bottles. We want it fairly small so that it does not leave the local park. We want to see how it will go in flight before it is put on a bigger rocket with a bigger booster. This staging mechanism will eventually go on the Acceleron rocket, but could be used for a third stage on the Polaron rocket as well.

A full write-up with diagrams of the internal operation will be posted on our main site once we have done the test flights and had a chance to evaluate its performance. Weighing in at 94 grams it is a bit on the heavy side for small rockets, but for bigger rockets it won't make much difference. Acceleron's V's staging pod weighed in at over 400 grams, but also included the parachute bay.
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Weekend Work

We worked on a number of different projects this weekend. We started a small production run of nosecones with integrated deployment systems using the new V1.5 flight computer. The idea is to build a number of these nosecones into our inventory so that we can simply screw in a new one should one become damaged. This will allow us to continue development on new projects without the need to spend a lot of time on repairs.


We also fixed up the launch release mechanism on the medium launcher after a hairline crack developed in the riser air tube. We have replaced it with a shorter much sturdier pipe that can be unscrewed. We also built a couple of swappable release heads with integrated launch tubes. The release head fitted to the release mechanism (image below) is a standard 9mm nozzle. The other two release heads are 15mm nozzles one with a 26cm launch tube to go into single bottle or robinson coupled rockets and the other has a 112cm launch tube to be used with longer, Tornado coupled and FTC rockets.


We've also did some more work on the new staging mechanism, but mostly just epoxying parts together.

We've fitted the endcap and nozzle on a full length of FTC now as we really want to get this first FTC rocket test flown. It will be launched with the new long launch tube shown above. There is still quite a bit of work to do especially on the recovery system.
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Flight Computer V1.5

The full construction details of V1.5 are now available here:

http://www.AirCommandRockets.com/flight_computer_V1_5.htm

Features include:

• Dual RC servo motor control
• 7-segment LED display indicating status information
• Built in launch detect G-switch
• External launch detect / burnout / negative-G trigger input
• Buzzer for indicating status and helping to locate lost rocket in tall bushes
• EEPROM used to store settings while power is turned off
• 15 configurable control parameters
• Altimeter/auxiliary power connector

The update includes a short video of the operation, as well as circuit diagrams and PCB layout.
We've got 10 boards done now and are in the process of populating 5 of them with components. We'll be switching all our rockets to these over the coming weeks as we put this version through various trials.


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Polaron VI to 637 feet

We had another great day this weekend launching rockets at the NSWRA launch meet. There was a unique opportunity to launch during a fog to see if we could get video from above it, and we managed to get a personal best altitude with our Polaron VI rocket on another flight.

Full details, photos and a highlights video of the day is available here:

http://www.AirCommandRockets.com/day61.htm

Repairs and New Development

This past week we have been making repairs to the Polaron V rocket as well as doing some new development for Acceleron.

All the plastic retaining tubes have been removed from the Polaron V main stage. On inspection one other tube was cracked (other than those that were shredded) . Because of the forces involved we didn't want to take any more chances with plastic, so we replaced them with thin walled brass tubes. Although adding a little more weight, they should be up to the job. We will need to do some tests first though before giving them the all clear. We are giving the PL a week to fully cure. Other than the tube replacement the rest of the rocket and boosters are ready to go. The plan is to launch the rocket at the next NSWRA launch event in a couple of weeks time.

Acceleron has been mostly repaired with the exception of the staging mechanism. Over the last month or so we have been working on yet another staging mechanism, and with the repairs needing to be done for Acceleron's staging mechanism we decided to complete it and put on Acceleron IV. We still have a long way to go with it, and need to do more testing, but so far the development has been going well. I will post full details once it has flown. It is a lot more compact and lighter than what was used on Acceleron previously.

Since we are rebuilding the staging mechanism it was a good opportunity to upgrade the Tachyon sustainer. We are building a completely new sustainer that has ~30% more capacity, more streamlined shape and new parachute deployment based on V1.5 of the flight computer. The fin section now integrates a ring fin with 4 smaller conventional fins. The ring fin struts are made from 6mm carbon fiber tubing and act as supports for the sustainer during the boost phase. The sustainer also carries both the altimeter and camera. As of last night the pressure chamber (3.35L capacity) is now complete, as are the 4 fins.

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Good Day / Bad Day

The details from the last launch day have been uploaded to the main site:

http://www.AirCommandRockets.com/day59.htm

Although it was a less than optimal day in terms of requiring repairs, we had a great day launching with other NSWRA members and even reached our highest directly measured altitude. With the same flight we also achieved our longest duration flight.

Repairs are already underway, and we are looking forward to the next launch day to fly Polaron V again.

We have also added a size comparison rocket gallery of our rockets built to date. You will need to have a flash player installed in your browser. Just roll the mouse left or right over the screen to scroll.
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Our First FTC pressure tests

We did our first T-8 FTC pressure test this weekend. Over the last two weeks we made up a 15 mm nozzle and an end cap that fit exactly inside the FTC. The nozzle is a standard 15mm Gardena style nozzle but one that comes with a threaded section. We made an adapter that allowed us to screw in the nozzle. The adapter has two grooves in it, one to hold an O-ring that seals against the FTC and the other allows the tube to be shrunk to stop the nozzle from flying out. We wrap some wire over the shrunk groove to keep the nozzle in place.

The inspiration for this retention setup came from Urie's water rockets. They have good photos of the nozzle and a good description of the technique.

When we tried to shrink the nozzle end by heating it with a blow torch, we forgot the fact that other parts of the FTC were also going to get heated. *doh* We ended up buckling a part of the FTC near the nozzle. Since this was only going to be a pressure test we didn't really care. Mind you when we were sealing up the end cap we filled the FTC with water, and that went a lot better.

The burst pressure was 190 psi (13.1 bar). The nozzle and end cap stayed in place so we were happy about that. This FTC is really thin walled compared to another length of FTC we got from Damo quite a few months back. The next test will be to wrap some of the glass strapping tape around it and see how much more *crossed fingers* it will hold.

You can see on the left edge where the FTC split.
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Flight Computer Q & A

Over the last year we’ve had quite a few questions about our water rocket flight computers so I’ll try to answer some of the more common ones here:

1. Why do you need a flight computer, wouldn’t a Tomy Timer do the same thing?
   
   When you only need a one-shot timer, we always recommend a Tomy Timer as they are inexpensive, you can get them anywhere, there is no need for batteries, very simple operation and light-weight. They are also a proven design.
   
   We wanted to be able to do more than just deploy a single parachute. A PIC-based micro-controller is an easy way to gain more functionality. Electronic timing is typically more accurate and repeatable compared to mechanical systems. You can also set very short timing delays for things like staging, something difficult to do with a Tomy Timer. There are elaborate mechanical systems that have been built that require no electronics that achieve the same thing.
   
   A flight computer can have: data logging capability, can control multiple actuators and have in-flight data processing and signal conditioning capability. If you wanted to experiment with active stability, or gather engineering data, it is difficult to do with a Tomy timer.
   
   
2. Isn’t it much heavier than a Tomy Timer?
   
   With our current design when you add the battery, servo and the flight computer it is perhaps 4 or 5 times heavier than a Tomy Timer. However, we use the battery for both the flight computer and the altimeter, so we save weight that way. The same battery could power the camera as well so you could save weight even further. We haven’t shared the power between the cameras and the flight computer yet.
   
   If you were to use a small lightweight battery such as the 4LR44, a 4.5g micro servo and surface mount components on a small PCB it could weight about double that of a Tomy imer.
   
   This weight difference translates to perhaps 10-20 feet altitude loss on small rockets and negligible on larger rockets.

3. Why do you call it a “flight computer” and not a “timer”?
   
   The terminology distinction is purely internal to our team. That way we differentiate between our simple electronic “timers” usually based around a 555 or 556 timer and the PIC based ones that have software running on them. Once the flight computer starts processing real-time flight data, the distinction will be more obvious.
   
   
4. Does it do more than timing?
   
   The published versions of the flight computers mostly do just timing. Although through software they also drive the LED display, do switch de-bouncing and generate the correct PWM signals for the RC servo motors.
   
   
5. Are you looking at adding more functionality?
   
   We have plans on our roadmap to add more functionality, but we are taking it one step at a time, experimenting with what actually works in the field what doesn’t. Take for example the various G-switch designs we’ve been testing. This involves multiple flights which takes time.
   
   
6. Does your current flight computer control your camera and altimeter?
   
   The published ones and flown to date have not. The altimeter is powered from the same power source as the flight computer. The Z-log altimeter can be set up to start recording 10 seconds after power-on which means when we turn on the computer, power is also supplied to the altimeter and it starts recording. But there is no direct control between the altimeter and flight computer.
   
   The V1.5 design has a free port left open to allow the altimeter to be connected to the flight computer through a serial connection. The Z-log altimeter outputs altimeter data continuously over its serial port. However, even V1.5 will not initially have it connected.
   
   The plan is to feed this altimeter data to the flight computer and it will be able to monitor the altitude and deploy parachutes at preset altitudes or when altitude starts decreasing after apogee. The flight computer will always use the timer capability for backup should something go wrong with the altimeter. At the moment we are working to make the timing as reliable and usable as possible before adding more complex functionality.
   
   It was always our intention to wire the old cameras to the flight computer so that they could be turned on by the computer just before launch since they only had 30 seconds of record time. However, ever since we bought the new FlyCamOne 2 video cameras with their 30 minute record time, the flight computer/camera integration took lower priority. We start the camera separately before we pressurize the rocket.
   
   
7. Do you have designs that you are keeping secret?
   
   No. We have no reason to. We only publish the designs once we have flown them a number of times. We like to verify the designs for ourselves before making them public, as it is much easier to fix things before publishing than having to make retractions or corrections later. We find it very useful in making the designs public as other rocketeers help suggested ways of improving them.
   
   We have already been contacted by 2 rocketeers that have built the flight computers based on our published designs, so we want to make sure we have confidence in the design before they are made public.
   
   
8. Isn’t it expensive?
   
   Not really. The PIC controller costs AUD$2.84, the handful of discreet components around $10, the batteries are about $3 and the cheap 9g RC servos we get for around $6 each. This means with a PCB the whole electronics ends up costing in the order of ~$25. That is about 1/4 of the price of the camera and about 1/5th the cost of the altimeter.
   
   Of the ones we have crashed we have been able to reuse most of the parts. Really the only things that do brake are the PCBs, the old G-switches and servos. We have now learned to protect the servos better and have had 2 survive direct impacts since the change.
   
   
9. Will they be available for sale?
   
   There are currently no plans to sell them in any great numbers as there really isn’t a market for them. Most water rocketeers prefer to build rockets out of inexpensive components. Personally I’d rather be flying rockets than handling order paperwork, chasing payments, etc. etc. We will likely offer 5 of the V1.5 for sale privately at cost price. (Contact us if you are interested - see contact page on our main site) The others we will continue to use for our experiments.
   
   
10. How reliable are they?
    
    So far we are having relatively good success with deploying parachutes and staging 2-stage rockets with them. All together there have been 68 flights with on-board flight computers, of which 5 failed to deploy and 2 successful deploys but tangled parachutes. This means as part of an integrated recovery system they are about 90% reliable.

11. What will be in the next version?
    
    V1.5 of the flight computer is the next iteration we are working on. This version has dual servo capability like V1.4, a loud buzzer for status feedback and helping to locate the rocket lost in tall grass or bushes. One of the new capabilities is that all the timing parameters are configurable in the field and stored in the on-board EEPROM to retain them after power is turned off. There are 15 parameters that are configurable from parachute/staging delays, to multiple servo positions, to the lost rocket sound alarm delays. We are having 9 more PCBs manufactured for this particular design as it makes it more compact and lighter.
    
    
12. 

12. Future plans?

Eventually we would like to miniaturize it and use all surface mount components and a much smaller PCB. The final weight and size should be similar to the altimeter (~10grams), although realistically this is at least a year or two away.

Adding logging capability will also be a priority in the upcoming months. We have ideas for air speed sensors that could be used to detect apogee, but have no idea how well they will work or what the data will look like. The idea is to use the normal timing for recovery, and the logging capability to capture data over multiple flights. We will do this for each type of sensor so that we can see what processing will be needed before it can be used effectively for apogee detection.

None of these plans for the flight computer are set in stone and are likely to change along the way. We only work on these during spare time and as a result the development is drawn out.

There have been many people who have flown flight computers on water rockets over the years, many of them a lot more advanced and using accelerometers, logging capability, running science experiments etc. The oldest documented reference I have found is back from March 2000.

Updated:

The following quote reproduced here in full is taken from a long exchange from the WRA2 forum and is included here because apparently we did not credit Bill with the invention of a water rocket flight computer and that we "stole" the idea from him. (See previous paragraph) In his own words:

Team Seneca Post subject: Posted: Tue Apr 15, 2008 12:13 pm

WRA2 Member
Joined: Sun Dec 31, 2006 4:40 pm
Posts: 97
Location: Seneca, N.Y.

It's not hostility. It's just that I never knew you guys would be so impressed with an electronic timer with a fancy name. I've put real computers on my rockets since the summer of 2005. A computer that does something too, not just a timer. I use an accelerometer to measure the flight and deploy. Back then I also used it to send signals to a small camera to take a snapshot at apogee. I'm the first one to put a computer on a water rocket and it was a real computer, not a tomy timer made from silicon.

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Bill W.
Team Seneca

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Polaron V Preview

Almost completed Polaron V. The main stage is close to 11L and uses a 7mm nozzle and jet foaming to produce a long a sustained thrust curve. The boosters are ~3.35L each and use a 13mm nozzle and normal water to get the main stage up to speed.

(Click on the images to enlarge)

The lower photo shows the detail of where the parachutes are stored on the boosters. It is difficult to see the clear strap holding them in place. A wire connected to the main stage releases the strap and the parachutes can fall out. In theory anyway. We are hoping things don't get tangled on release as there will be three wires hanging from the rocket, parachutes popping left right and center and the clear straps are spring loaded so they will also be in amongst the action.

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Quick update

We've been progressing this week with the Polaron IV upgrade. The booster parachute deployment mechanisms are now finished on all three boosters.

I made an extra reinforced bottle for the main stage, but after gluing and heat shrinking I noticed that the coupling was sitting at a bit of an angle. This would have resulted in bent rocket, so I tried to straighten it, but instead of improving it, I managed to break the coupling. :( So I threw that bottle away and had to make up another one. The whole process takes about an hour to reinforce the bottle. We are waiting for the glue to cure before we do a full pressure test.

We've reserved Friday for a full pressure test of the new main stage and new boosters as well. If the weather is favourable we'd like to fly it on Saturday.

We also did some experiments this week in creating foam in a bucket by blowing air through a sintered metal filter into the bubble bath solution. The tiny holes help make foam more readily. We want to try generating foam on the pad to see how it compares with it generated in the air. The main observation was that if the air flowed too fast then the bubbles would re-combine into larger ones, but a slower rate created more smaller bubbles.

There have been some really good discussions on the Yahoo Water Rocket forum this week regarding internal temperatures. It may help to explain why we have had some unexpected failures of the bigger boosters under test. I'll cover this in more detail in the next web update.
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Progress Updates

We have updated our main site with a few more details of what we've been up to in the workshop. The update also includes some great pictures from the last launch day taken by Andrew from NSWRA.

The update is here: http://www.AirCommandRockets.com/day58.htm



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Tornado Couplings

This weekend we finally managed to produce a number of good Tornado couplings. Tornado couplings connect bottles neck to neck. These one's are easy to make out of gardening supplies from the local hardware store.


Some features:

• They have a 15mm hole
• Weigh 13 grams
• Require no glue
• Have been tested to 130psi, but can most likely hold more.
• Require no special tools
• All plastic construction - no metal.

We have been wanting to make these cost effectively for a while now since we plan on using lots of them to join the spliced pairs of bottles. We will give full construction details in future updates on the main site. We want to put them to use first on the Polaron IV boosters to extend their capacity by another bottle each.

We are also currently working on another staging mechanism design that will be hopefully a lot lighter than the one we have been using on our two stage rocket. Since we are still in the early stages of development, we will describe the design later, once it is more finalised. We have lots of testing and prototyping to do still.
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2 Stage flights

We had a great weekend launching our rockets at the NSWRA launch event. We flew our newly rebuilt 2 stage Acceleron IV rocket up to 525' (160m). We also flew the Polaron IV rocket with drop away boosters to 510'.

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

http://www.AirCommandRockets.com/day57.htm

Here is an panorama from around 500' as the rocket pitched over at apogee.
(click on the image to enlarge)

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Acceleron IV progress

We spent this weekend working on the Acceleron IV booster getting it back into a working state for next week. We did a pressure test to make sure that everything is still fine, but we found out that the rocket was not holding pressure at all. We pretty quickly discovered that three of the Robinson couplings were missing their seals. Ooops. When we put those back in and everything checked out okay. We must have missed them during preliminary assembly.

We only pressure tested the rocket to ~100psi since the neighbours were out in their back yard, and having had this rocket fail a pressure test in the past, we didn't want to push it. We did have the video camera recording though just in case. The rocket will most likely get launched at 120psi on the day. The rocket theoretically should hold up to around 140psi operational pressure, with a burst pressure of around 180psi.

We hooked up all the electronics and and made sure the staging still worked when the pressure in the rocket dropped. We replaced the sustainer in the test with a small bottle full of water which fired as expected.

We replaced the rubber bands in the staging mechanism as keeping them stretched all this time in storage caused them to deteriorate quite badly. The same went for the wide rubber bands that held the fins on.

The booster segments are now attached with velcro straps which makes it a lot easier to service the segments.

The launcher has also had an upgrade with new longer fill tubes that allow us to use the spliced pairs of bottles on the bottom of each segment.

Some work has also been done on the sustainer. The altimeter has been moved into the space between the bottles which should help protect it. The altimeter is attached to the inter-bottle ring and having its own power supply allows us to swap it between rockets. We still have to re-attach the fins to the sustainer and also mount the new FlyCamOne2 camera to the payload section.

If we get time this week we also want to finish building a reinforced rocket that should be capable of around 180-200psi. It is only a two 1.25L Robinson coupled rocket but we are including the baffle we made a few months back to prevent the blow through effect with this rocket. The higher pressure would only make it worse.

We also made a couple of rocket carriers that help us transport and protect the rockets. They also help prevent the rockets from sagging in warm conditions.
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Flight Computer V1.5

Last night I finished soldering up the new board for the latest flight computer. Everything worked as expected which is good, and we will fly it soon.


The large bright LED display allows you to stand back from the rocket while it is pressurised and ensure the correct settings are set. It also has a small buzzer that allows you to hear whether it is armed or not while standing back.

A little more software needs to be written for the flight computer to support the new functionality. The intention is that the code base will be universal enough to be used for regular water rockets, but also for multi-stage, or dual-parachute.
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Launcher Details in 3D

We spent this weekend documenting our Polaron IV launcher and rocket. We've produced an explanation video of how the launcher works as it is much easier to explain the configuration.

The details are available here:

http://www.AirCommandRockets.com/day56.htm

The update also includes a number of anaglyphs of various parts that you can view in 3D using regular red-blue 3D glasses.

Click on the image to enlarge.
You will need red-blue 3D glasses to see this image properly

Also a quick update on flight computer V1.5 - We received our first PCB this week so we are keen to solder it up and see how it performs. If no changes are required we will get another 9 PCBs made so that we will have total of 10 flight computers ready to go for the up coming experiments.

The new flight software is also progressing and should be finished within the next couple of weeks. Once the flight computer has had a successful couple of test flights, we will publish the full design again, including the PCB layout.

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Parachutes

After a short break last week to catch up on non-rocket related projects we are back in full swing again.

We ordered some great lightweight ripstop nylon parachute material from the UK this week. It was comparatively cheap at only AUD$32 delivered for 10m x 1m of the stuff. It is a nice orange that should make it easily visible. From the time of order to delivery it only took about 6 days to get here which is pretty fast considering it had to go half way round the world.

We want to make a new lighter parachute to replace the one on the Polaron rocket. The parachute will weigh less than half the weight of the existing one, and also use up about half the space. For the shroud lines we are going to use TigerTail - a very strong light-weight line typically used for making necklaces. It is stranded stainless steel cable coated with nylon. It is very light, doesn't kink, is only 0.3mm thick and has very high tensile strength. This will allow us to make a strong parachute and should pack into a much smaller space.

If this parachute goes well, we will most likely make up more parachutes for the other rockets, including Acceleron.

We have also been doing some more work on flight computer V1.5 and hopefully the prototype should be ready soon. We are getting a number of PCB boards made up so it will take up minimal space and weight. Once finished it will be used on all of our rockets as it is capable of driving two separate servos and has a few more nice features compared to the previous version.

I turned off comments here on blogger (temporarily) due to excessive amount of SPAM last week, so if you would like to ask questions, just visit the main site and go to the contact page.
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Polaron IV Boosted flights

We had a great weekend of flying the Polaron IV rocket with the drop away boosters. The boosters behaved exactly as expected and gave the rocket a nice kick on launch.


The on-board video also turned out great.

The full details of the launch day with lots of pictures and video of the highlights is available here:

http://www.AirCommandRockets.com/day55.htm




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Successful Booster Test Flights

In preparation for launching Polaron IV we wanted to make sure that the whole launcher will work with the boosters and the main stage all together. We weren't sure if it would come off the launcher cleanly, or if the boosters would fall off, or how the new guide rail would go.


We built a dummy main stage out of old bottles and an old nose cone that used the nosecone-off-at-apogee technique for deploying a parachute. The main stage only had the bottom 2 L bottle pressurised. And had 1.5L of water in it so virtually no air. We added a little ballast into the nose in the form of a zip-lock bag with water in it.

We had two successful vertical take-offs with the boosters all falling off almost simultaneously on both occasions. The boosters were filled with 1L of water and everything was launched at 100psi.

The dummy main stage weighing in at close to 800 grams was still able to reach ~80-90 meters
The parachute opened on the first flight right at apogee, and failed to open on the second flight.
The dummy main stage was destroyed, but luckily all the bits we needed for the Polaron IV rocket survived. The boosters also survived their tumble recoveries.


We proved to ourselves that this particular launcher and booster concept works, and so we are hoping to get at least one flight out of the Polaron IV rocket on Saturday. There are always things that can go wrong on the day, but we will worry about those when they happen.

We have also finished repairing the Hyperon and J4 rockets, so we will have those as backups on Saturday as well.

Full details of the days events with videos of this booster test will be again published on our main site after the launch day.
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Launcher Completed

We spent most of the day in the workshop again today. We are really pushing hard to get Polaron IV and its launcher ready for the next NSWRA launch day. It is only 6 days away.

We did finish the launcher today, which I am really happy about. It now sports a single 2m launch rail. The rocket will use launch lugs to hold onto the rail. We had to switch to this system since there really isn't room for the 3 guide rails we have been using. We ended up using 2 of the feet and guide rails from our medium launcher to support the new launch rail which really reduced the amount of stuff we had to make. The legs are still usable on the other launcher so the nice part is we have less hardware to carry with us when we take both launchers.

We are now finishing off the rocket and the booster retaining mechanisms on the rocket, and then it should be ready to fly. If there is a nice launch opportunity between now and Saturday we may try the boosters with the dummy main stage at our local park.
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Splicing Bottles and Pressure Tests

The weather hasn't been too co-operative this weekend so we spent quite a bit of time in the workshop. We have updated our main site with the latest developments here:

http://www.AirCommandRockets.com/day54.htm



The update includes a video tutorial into how we splice our bottles. It also includes an update on the progress of our Polaron IV rocket, and the Acceleron IIIb booster.
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Glueing and PCB layout

Splicing and Couplings

This week it's been a bit of a mixed bag. Now that we have the PL Premium glue, we are gluing together pairs of 1.25L bottles. These glued sections have a thread at either end allowing us to join them to other sections. We have 6 made up, and two more will get made today. They will be used in constructing boosters and rockets bodies as well.

To join these together we have also been experimenting with making simple "Tornado" couplings. We are still waiting for the glue to dry before we do a full pressure test. We've made up four of these so far and if they work well, we have the materials to make a lot more. They weigh around 7 grams. The other nice thing about these couplings is that they have a 19mm hole which is about 6 times bigger in cross sectional area than the Robinson couplings we have been making. This leads to better internal efficiencies and also means we can put a long 19mm launch tube through them.

The simulator predicts well improved altitudes for rockets made out of the spliced pairs and the tornado couplings.

Repairs

We have also been doing repairs to the two crashed rockets from last week. This will require a little more work since the nosecones and deployment systems need to be rebuilt.

PCB Layout for Flight Computer V1.5
As a part of making life easier when doing repairs we have been finalising the PCB layouts for the next iteration of the flight computer. We are going to do a small run of these PCBs and make up a number of the computers so that we can quickly replace them should they become damaged. The board will be about 43mm x 55mm in size or about 30% smaller than what we have been making on the prototype board. It will have dual servo motor outputs making it suitable for single and dual stage rockets. It also has a buzzer for audio feedback of mode changes as well as helping to locate it in tall grass.

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Launcher Pressure Test

In the last few days we've pressure tested the Polaron IV launcher to make sure there are no leaks. There are a lot of connections and we were not sure how well the seals would seal around the plastic compression seals around some of the copper manifold pipes.

All was good and we took the pressure up to 215 psi ( ~15 bar ) for both the main stage line and the booster manifold.

When pressurising, we really have to think about what valves get open or closed and in what order.

For the first launch the pressures will be in the order 110 - 130psi.

We made dummy plugs for the booster nozzle seats for the test. This allowed us to test that side of things without having to put the boosters on the launcher. We fitted a strapping tape reinforced small 300ml coke bottle to the main stage release head and used the 7mm aluminium nozzle that the main stage will use. All held up well, and we tested the bleed valves
for both the main stage and the boosters with success.

We are now working on the booster retention mechanisms and getting those attached to the boosters and main stage.

The update from last Saturday's launch event is also now available on the main site:

http://www.AirCommandRockets.com/day53.htm

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NSWRA and Polaron IV Main Stage

Yesterday was a fantastic day for rockets. We are now members of the newly re-grouped NSW Rocketry Association (NSWRA) and went to one of their launch events at Doonside. There were many rockets flown on the day and we got a chance to fly three of ours.


We ended up finishing the Polaron IV main stage rocket at about midnight the night before and so we got a chance to test it. We flew it twice with the full payload (new camera, altimeter and flight computer). Both flights were very good and the new parachute also worked well.

The Polaron IV rocket is now pretty much ready to be fitted with the boosters and ready to go. We will probably run some tests first on the boosters being launched from the new launcher with a dummy main stage.


Full details of the flight day will be published shortly with pictures and videos.

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Black Tape and Sun

As I was inspecting a couple of our rockets last night and getting them ready for tomorrow's launch day, I noticed that the bottles were warped in a couple of places. It appears that the warping was most severe where the wide black tape was. This also occurred on the unpressurised sections of the rocket.

This was likely to have been caused during the last launch day when we left the rockets sitting out in the sun for a couple of hours. The heat absorbed by the tape was enough to shrink the bottles a little under the tape.

This is likely to occur to other rockets that are painted in dark colours. I think we will be storing our rockets in the shade from now on, and perhaps switch to lighter coloured tape when the black stuff runs out.

I spent most of the last couple of nights trying to get the Polaron IV main stage ready for flight on Saturday. The payload section now has the new FlyCamOne camera built in, the Z-log altimeter, servo motor, batteries and a newly built version of our flight computer (V1.3.2). I just have to attach the door and latch mechanism to the payload bay and then attach the whole thing to the rocket body.

We want to test fly it by itself to make sure all the systems and recovery works before we attach the boosters to it.

If we do get to fly it this weekend, I will post pictures soon after that.
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Booster Tests and Launcher Details

We've updated the main site with the latest details of the Polaron IV launcher and the new Gluon boosters.
The name Gluon was chosen because it continues with the sub-atomic particle naming convention we have been using for our rockets and also because it is our first operational spliced rocket using PL Premium glue.

The update can be found here:

http://AirCommandRockets.com/day52.htm

The update also includes a video of the booster tests. It's not overly exciting but included for those who are interested.

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Launcher and Booster Tests

We've had a very productive weekend this week. We completed the majority of the new Polaron IV launcher, spending about 8 hours in the workshop on Saturday.

The image below shows the state of the launcher currently. I will do a full update this week and post it on our main website that shows all the details and discuss some of the design issues.

On Sunday it was too windy to launch regular rockets and so we opted to do a number of booster test launches. We fitted a booster with a regular nozzle and launched it from our medium launcher. The main aim of the test was to see how the booster behaved in flight and how its recovery system would work. Full details of the booster will also be posted with the next web update.

The larger parachute is now finished for the Polaron IV rocket and the payload section is also well under way. With the altimeter, flight computer, and video camera, the payload section alone is worth around $300. Hmmm... I think I will add a padded nosecone extension for protection in the trial flights. This padded nosecone will be removed for the higher performance flights once the design is proven.
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Holidays over

Having been OS for the last 3 weeks the holidays are over, and we are back in full time production of the Polaron IV launcher and rocket. We are concentrating our efforts on this in order to get it done as soon as possible. During the holidays dad machined up a lot of the necessary components for the launcher, and now we are pretty much ready to start assembling it all together. Dad also did a bit of work around the workshop putting up some new shelves and fixing a few things making it easier to do development.

The Polaron IV rocket will also be fitted with one of the new FlyCamOne cameras as well as the altimeter. I am weighing up whether to build the next version of the flight computer for this rocket or just use one of the existing ones. I may use V1.3.1 in the first few trials and then upgrade when the next version is finished.

This weekend looks like weather is not going to play ball so workshop time is in order. Hopefully we can get most of the launcher done.

This launcher is intended to take us up to the next level in rocket pressure and size. We eventually intend to be launching reinforced rockets from this launcher and hence it is being designed to handle 35bar (500psi) operational pressure. It will support both single nozzle rockets as well as rockets with 3 boosters. The booster nozzles can slide in and out allowing us to used different sized boosters and main stage.

I'll take some pictures over the weekend of the launcher and post them here or on the main site.

PL Premium Glue

We still have a number of tubes of 10oz (300ml) PL Premium glue available so if anyone in Australia is interested please let us know. Just email me: katz.george at gmail.com.
The tubes are AUD$8 each + shipping from Sydney. Standard postage rates apply. You can check the Australian Post office website for shipping charges.


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Katz Stager and new cameras

Katz Stager

While developing our regular rockets we have been working on a new staging mechanism in the background - the Katz stager. We normally don't release details of concepts until we test fly them, but since it's been a while that we've done an update I thought I'd include it. We have built a prototype and test fired it a number of times by hand, but it is still to fly and at full pressure.


The full details of the stager and photos of the prototype can be found here:

http://www.AirCommandRockets.com/day51.htm

New video cameras

We have also bought a pair of FlyCamOne V2 video cameras this week. So far we are very happy with the functionality and performance of these cameras, and are looking forward to mounting them inside rockets and flying them. They can record video at 640 x 480 resolution @ 25fps with sound, which is not bad for a 37 gram package. Recording onto an SD card allows you to get up to 30 minutes of video. Compare that to our existing cameras that record 320 x 240 @ 15fps and can only capture 30 seconds of video.

The other nice feature is the optional external power supply, the swiveling lens+sensor for minimal drag in the air stream and external shutter contacts to allow a flight computer to trigger recording or take 1280 x 1024 pictures.
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