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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