2 great flights, 2 crashes

We had an overall great day at NSWRA's launch event on Saturday. We got to fly the newly rebuilt Polaron VIb rocket that hadn't flown since May last year. Both flights were almost perfect with very nice vertical flights, and no spin which made for great stable ascent video. Although we had tested the bottles to 130psi, we only launched at 120psi to be on the safe side. During testing earlier in the week, we had 3 out of 4 spliced-pairs leak. So only the bottles that had withstood the full 130psi were used in the rocket. We were very happy with the performance of the rocket, and were glad that the stability improving changes we made had been effective.

While other NSWRA members were drilling holes in the clouds (literally) with their impressive pyro rockets we were busy taking core samples near the launch pad. One was the FTC rocket and the other was Axion II. Full details of the crashes will also go in the update.
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Progress update

We've posted an update on main site that describes some of the things we have been working on lately. At the moment we are trying to get two big rockets (Polaron VIb and Polaron VII) completed by the NSWRA launch event next week, as well as the FTC rocket. Currently they are still in pieces, but should be assembled in the next few days.

The update is here:

http://www.AirCommandRockets.com/day72.htm
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Flight Computer V1.6 Details

We've put up the full details of the latest flight computer on our main website here:

http://www.AirCommandRockets.com/flight_computer_V1_6.htm

There have been a number of changes since version 1.5:

• The altimeter power connector has been removed. The altimeter can still be powered via the second servo connector. If both servos and altimeter are used then the second servo can be connected to the altimeter's pass through connector to connect the second servo motor.
• The PCB is now double sided resulting in less weight and 25% smaller area. The PCB is also only 27mm wide allowing it to be used inside T-8 and T-12 FTC tubing.
• The timing parameters have been changed to represent seconds directly rather than the more confusing offset/multiplier technique used in V1.5. Although the direct setting reduces the range of values possible, they should cover the vast majority of situations as used in the real world. The timing for both D1 and D2 phases can now be set between 0.1 and 99.9 seconds in 0.1 second increments.
• The setting of the two delay parameters in the Normal mode have been removed and the FC now simply requires one press of the ARM button to ARM it. This was done to make it simpler for the rocketeer to use in the field, and prevent accidental timing changes.
• The servo control pulse width range has been extended to allow driving some non-standard servos their full range.

These are now available for purchase. (Includes FREE worldwide delivery!)

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FTC nosecone success

Well nosecone attempt #4 (see below) worked out as planned.


This is the end result of 8 layers of nylon stockings with polyester resin, one thin coat of 5 minute epoxy, thin coat of spray on putty sanded back for a smooth finish and a couple of coats of gloss paint. Ideally the polyester resin will be replaced completely with epoxy. I will update the nosecone build procedure with the next main website update.

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FTC Nosecones

Since we are rebuilding the FTC payload, we've decided to replace the Kinder surprise egg nosecone with a more streamlined one. I machined up the nosecone mold out of a solid piece of plastic and polished it.

The nosecone mold prior to final polishing.

Attempt #1 - Heated the base of a small PET bottle and forced it over the nosecone mold and tried to heat shrink it over the top. Heat gun was too close and the base started crystalizing. The nosecone ended up flying quite nicely into the rubbish bin.

Attempt #2 - Heated the base of another small PET bottle more gently this time. This was only a slightly better result than the previous one. Before long he joined his friend in the bin. It just could not be shrunk down enough to the 30mm diameter.

Attempt #3 - Coated the mold with release agent and impregnated fiberglass matting with resin and then started wrapping it on the mold, but as you can imagine a nosecone isn't easy to round off with flat matting. Before long I had a nice mess on my hands with lots of bubbles, folds, and the rounded front was anything but. After another 5 minutes of trying to correct it, I finally pulled the whole mess off the mold and guess where it went?

Then I emptied the bin ready for more nosecones.

Attempt #4 - I went to the local supermarket and bought a couple of pairs of pantyhose (nylon stockings) and a shoe polishing brush. Okay I did get strange looks at the checkout counter as they were the only things I purchased. Little did they known those stockings will do over 200km/h one day. Instead of the release agent, I stretched the thumb section of a disposable rubber glove over the mold and tied it off. This made sure there were no creases anywhere. I then proceeded to stretch 8 layers of pantyhose over the top of that again tying it off at the bottom. I then simply poured the fiberglass resin all over it and worked it in with a brush and with my gloves. The nosecone is now drying so I will know in the morning if it worked. Otherwise it looks pretty good.

... Oh and the shoe polishing brush I bought earlier I had cut into about 20 strips each with 5 sets of bristles and use them as disposable brushes for the fiberglass. At 10c per strip they can be thrown away after each job.

I'll post results of attempt #4 when it dries and assuming I can get it off the mold.

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FTC rocket upgrade

We've been working on a number of rocket related projects this week. We started redoing the FTC payload bay that includes several improvements. We are replacing the split nosecone made from FTC to one made from Fiberglass. The fiberglass is a lot stiffer, but still lightweight and does not collapse like FTC does when it is cut in half.

Because we used a piece of FTC to form the half-shells, their diameter is also the right size for fitting over the FTC tube. The V1.5 flight computer used is being replaced with the smaller V1.6, and the batteries are being replaced with four AAAAs. The net result is a more compact payload section that is a little lighter than the predecesor. We are also creating smaller fins for the rocket to reduce the overall weight near the tail.

We have also tested an all-Sikaflex splice this week with the glue failing at around 130psi. The glue had given way, as both the sleeve and the bottle that was glued inside the sleeve were undamaged. The glue was left on both surfaces. This means that this glue probably should not be used for pressures above 100psi. We have a number of spliced pairs using this glue already made for the Acceleron rocket, so we will have to replace them with PL splices. We can still use them on other test rockets so we will hang on to them.

Fiberglassing is definitely a messy business but I'm getting used to it a bit more now. Last week I bought a proper respirator with organic gas filters for $45 and its really effective and I can't smell any of the resin when working with the fiberglass.

As we are working on a lot of spliced pairs at the moment, there is quite a bit of sanding to do of the surfaces to be glued. We always used to do it by hand, but we've made it a little easier now by getting a piece of PVC pipe and cutting a pair of long slits in it. We then take two rectangles of sandpaper and put them back to back and place them in the slot. The pipe then goes in the lathe. When it spins the sand paper makes a kind of S-shape and makes it much faster to sand the outside and inside of the bottles. It reduces sanding time by about 1/3 and also is alot easier on the hand strain.

Soldering up the flight computers has also been performed in the background in spare time, and documentation continues to be worked on.

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V1.6 PCBs have arrived

We received the PCBs yesterday from the manufacturer. I was very impressed with their quality, and breathed a sigh of relief when all the components fit. :) We'll definitely be using this manufacturer again. I was keen to see if the layout design would work but unfortunately we had a blackout and so I had to hold off on soldering the first unit until after dinner.

Breathed another sigh of relief when the FC powered up first go. The software is pretty much done, just doing a few more minor tweaks to the servo timing routines and testing it with a range of servo motors.

The version shown above has the assemtech G-switch soldered in and it's set up for 9V operation. With the battery clip the FC weighs in at 18 grams.

Next up we are going to do some flight tests with them, and I'll replace the V1.5 FC in the FTC rocket with one of these to see how it performs under higher G-loads.

The documentation and manual still needs to be completed, but that is also close to being done.

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Fiberglassing

Last weekend we went out to Doonside with some of the NSWRA rocketeers but only equipped with lawn mowers and brush cutters. All the tall grass is now gone from the launch area so it is a lot nicer to move around and set up. Phil also installed permanent launcher bases which will make setting up much easier and there is less gear to bring each launch day.

While we wait for the new flight computer PCBs to arrive (Apparently they have now been shipped) we have been continuing to build the Acceleron V booster. We have mostly been testing and reinforcing the 2L spliced pairs. The booster uses 9 of them. We splice a pair together and then hydro test it up to about 80 psi. If there are no leaks we then add the neck reinforcing rings and wait a few days for them to dry, before testing again to 130psi. This way if the original splice fails at the 80 psi we don't waste time and bottles reinforcing the necks. The neck reinforcements are necessary as at about 110psi stretch marks begin to appear around the neck of the 2L bottles.

We are making a few spare spliced pairs in case any need replacing. The spare ones can later also be used for the new bigger Polaron boosters. A couple of the pairs are all-sikaflex splices so we are keen to see how they hold up.

I have also had my first go at fiberglassing. I wanted a simple project initially to learn the technique and so decided to make a ring fin that should be able to withstand a bit of punishment during tail-first landings under parachute. It was quite easy to do but I can see I need to pay a bit more attention in getting all the bubbles out and work a bit more at getting the resin in all the way through. But overall I was pretty happy with the results. The ring fin is 37 grams, 0.8mm wall thickness and uses 3 layers of fiberglass matting. It is significantly stiffer than a PET ring.

Here is the ring fin after the first rough sanding. I'll spend a bit more time making it smoother before painting it. The ring fin will be attached with CF struts to the main rocket body.

The next few fiberglass projects will likely to be fin strut attachment supports for the pressure chamber, and reinforced balsa fins. When I get a bit more comfortable working with it, I'll have a go at reinforcing some pressure chambers.

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Progress Update

This last week we have been concentrating on getting the FC V1.6 finished. It has taken a little longer to get the PCB designed as we are still learning the Eagle CAD package, but the package is definitely an improvement over what we were using before. We are also using a new PCB manufacturer so some time was spent configuring Eagle's layout tolerance settings specific to their manufacturing process. The boards are currently being made so we hope to have them within a week or so, and then we can start soldering. :) We've also been creating all the documentation that goes with it.

Rocket development otherwise is progressing slowly at the moment as most spare time has gone into building the bigger workshop.

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New Year & Recovery Guide

Recovery Guide

Happy 2009 to all! With the busy time of Christmas over we are now back to more full time rocket development. One of the things we have been working on over the past few months has been a water rocket recovery guide.

The recovery guide is intended for rocketeers wanting to add a recovery system to their water rocket. The guide covers the multitude of approaches rocketeers have taken over the years, discusses some common misconceptions and provides links to various websites covering all aspects of recovery.

The current iteration of the guide is here:

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

This guide will continue to evolve as more systems are documented and as more links are explored. If you have a recovery system you'd like to share that is not on the list please let us know either through the guide's form, email, or comments on this blog, and we'll classify it and add the references to the relevant sections of the guide.

Plans for Air Command in 2009

Some of the things we are planning for the first half of this year:

• Continue work on the recovery guide.
• Release V1.6 of the flight computer. The new version has a PCB around 25% smaller than V1.5 and is designed to fit in regular rockets as well as T8 FTC. It is also simpler to set up and use. A small quantity of these will be available for sale. We are aiming to release by end of January.
• 33L Acceleron V development. We have a lot of pressure testing and reinforcing to do on this rocket and we may need to upgrade the Acceleron launcher for bigger nozzles. We're looking forward to the flights of this one. :)
• Polaron VI rebuild with larger boosters.
• Baryon III multi-stage flights - Actually trying to get the second stage separated properly this time. :)
• Continue with the static testing. We have a number designs we would like to evaluate.
• Fiberglassing body tubes for stronger and higher pressure rockets.

We look forward to seeing everyone's progress this year.
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FTC flights update

We've updated the main website with the FTC flights report from last Sunday. Included is a short video of the highlights from the day.

http://www.AirCommandRockets.com/day71.htm

In putting together the pictures and video for the update we noticed that in both of the last two higher pressure flights the rocket was bending quite a bit on take off. This probably explains the lower than expected altitude. The rocket is very flexible and under the acceleration loading it just bends. This is likely to be inducing fairly large drag.
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T8 FTC rocket flights

We had perfect launch weather this weekend, but since it wasn't a NSWRA launch day, we went back to our old launch site to test fly the FTC rocket and check out all its systems.

We had to launch at a lower pressure in order to keep the rocket in the park. We launched the FTC rocket 4 times and also launched a number of other rockets on the day. There were no crashes on the day so we were happy.

We are putting together another update for our main website with more pictures and a video of highlights from the day. This should be available in the next few days, but it may be after Christmas depending on how we go for time.
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Still Here

In the lead up to Christmas we've had to curtail rocket development as we are busy with family and work related obligations. Development is still continuing in the background although not enough for an entire update. I am waiting until the start of the holidays to have more time for development. We will also be extending the workshop under the house to have more room for building and storing larger rockets.

Since the NSWRA picnic was also canceled due to bad weather we haven't had a chance to launch our FTC rocket yet. We will try to launch it on a weekend at the local park at a lower pressure to check out all systems. If all goes well, we will launch it at full pressure at the next NSWRA launch day.

We hope everyone has a great Christmas and a safe new year!

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Software

We've been spending quite a bit of time this week writing and testing the FC V1.6 software. We are making it a little more user friendly to set up and operate in the field. The delay, offset and multiplier parameters were more difficult to set because you really needed to have the manual with you. Although you loose the precision of V1.5 the new settings allow you to set the time directly, so you can quite easily set it in the field. The settings allowed, however, should cover pretty much most flight profiles.

This also has meant that we've needed to update the operator manual which will be published when the FC is finished.

Last weekend was supposed to be a launch day but the wet weather cancelled those plans. :( NSWRA is meeting again this weekend so we will try to make it, but at this stage I'm not sure since family commitments were scheduled around last launch day and can't be moved. In any case NSWRA is meeting again the following week for a launch/picnic day, so we should be able to make it to that. We have four rockets itching to get off the pad, so they'll need to wait a bit longer.

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Open Day, G-switch, Acceleron V

We've update our main website with the latest development progress on a number of fronts.

http://www.AirCommandRockets.com/day70.htm

I've spent most of last night doing final work on the FTC rocket to get everything well secured. The rocket has also had another pressure test to 180 psi without any visible issues. Phil had a good suggestion to re-string the nosecone so that the parachute is attached to the nosecone and the nosecone is attached to the rocket. In this way more tangles can be avoided. I've also been a bit concerned at the forced on the top of the rocket where the parachute is attached. The main worry is that a high speed deploy could separate the payload section from the rest of the rocket. I've now threaded another kevlar line through the full length of the payload bay that is attached firmly to the pressure chamber end cap and the other end is looped through the main parachute line. Should the parachute rip off the payload bay, it should all remain connected to the rocket.

We are hoping for nice weather this weekend so we can go flying.
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Open Day Preparation

We've been flat out this week trying to get things ready for the open day this Saturday. The main project has been a rebuild of the Acceleron booster. This is our biggest booster to date at ~33L capacity. Acceleron III was 24L and Acceleron IV was 18L because it used 1.25L bottles.

The new booster has three 2L bottle spliced pairs tornado coupled together per segment. There are three segments in total. At 130psi the pyro rocket equivalent is an H310. (~250Ns total impulse)

We have simplified the pod at the top of the booster. The deploy mechanism is the same as the previous versions of Acceleron based on a FC, pressure switch and servo, but the parachute is no longer located in the pod. This meant that the pod could be smaller and lighter. The parachute now resides between the bottle necks of one segment so there is no extra drag. The parachute will be deployed using the piano hinge technique we have been using recently. This should mean the parachute opens sooner. Too many times before the parachute deployed late.

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Batteries and FC V1.6 progress

Batteries
I'm always on the look out for small yet moderately powerful batteries to power the on board electronics. It's always a compromise between cost, weight, voltage and current capacity. I've been using the Lithium CR123As in pairs to give me 6V but the amount of current they supply is much more than I need and hence are unnecessarily large. 9V batteries are pretty good in price, voltage and current but are comparatively heavy ~45 grams. A stack of button cells generally cannot supply enough current to drive servo motors.

When cost isn't an issue and you are after minimal weight and maximum power density then I expect some of the tiny Li-po batteries are the way to go. But they do need a charger, are expensive and not readily available.

I came across this video a few weeks back, and finally had a go at pulling apart a 9V battery this week.

http://au.youtube.com/watch?v=tr5ZB1eFhwc

Judging by the YouTube video comments a number of issues need to be looked out for:
- Only go for Energizer or Duracell alkaline batteries
- Don't short anything out while doing so.
- Wear gloves should you spill some acid

I only need 6V to power all the electronics so 4 of the cells are all I need. It also means that getting two 9V batteries I can make up three 6V battery packs. At only a few dollars per battery pack it means they are very affordable, and available everywhere. After removing the casing, connectors, and two cells the weight of the battery drops from 45 grams to 25 grams. In comparison a AAA 6V battery pack weighs ~44 grams, and AA battery pack weighs ~90 grams.

I just soldered wires to the contacts to make up the connections. I have started doing this ever since we found that some battery holders under G forces can easily loose contact. They powered the flight computer and servos just fine.

The small form factor means that they can be rearranged to fit the available space.

Flight Computer V1.6

I've ordered all the parts now for the next iteration of the flight computer. This will be a slightly larger run of 20 compared to the 10 made for V1.5. I am waiting for all the components to arrive first in order to verify their dimensions before finalising the PCB. I'm also investigating a small and cheap G-switch option to trigger it rather than the commercial G-switch costing around $9. The PCB will be designed so both variants can be used.

The updated software is also almost finished. We had a request come in from a water rocket team (Oberon WR) who built version 1.5 of the FC but their servo was only turning only around 90 degrees even though the full range of movement was 180 degrees. We tested this with one of our cheap 180 degree servos and sure enough the full range was around 90 degrees. I checked the PWM signal on the CRO and the standard range of ~1ms to ~2ms was correct coming out of the FC. I updated the code to give a range between 0.5ms and 2.5ms and that gave the full range of the servo movement. If I have sent you a copy of the V1.5 code, I can send you the update if you have this issue. Other servos worked fine with the 1-2ms timing.

It seems that some servo manufacturers don't adhere to the standard 1-2ms for full range. This change will also be rolled into V1.6. It may end up as another configurable parameter: 1-2ms for full range or 0.5 - 2.5ms for full range.

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FTC Parachute Deployment Mechanism

We've posted an update on our main website with details of how the T-8 FTC parachute deployment mechanism works.

http://www.AirCommandRockets.com/day69.htm



Included in the update are photos and a short video of how the mechanism works. We are hoping to test fly it at the next opportunity.

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Sewing on fins

We decided to sew the fins to the FTC rocket. Hopefully this will provide additional strength for the expected G forces. Okay so it's not your ordinary needle and thread but the idea is the same. The wire threads through the split sleeve and through the fin. The wire does not go through the pressure chamber.


PL premium still provides the majority of the strength, but the wire is there to ensure the fin does not come off should the glue fail while the rocket stretches during pressurisation. The wire also keeps the fin in place while the glue dries.

Once the initial glue dries the wire is trimmed and the twisted part is folded down and a more glue is used to create a fillet on either side of the fin. We are trying a technique to minimise the amount of bubbling from the PL, as PL is not very nice for smooth fillets. After we form the smooth fillet with the PL we place scotch tape over the fillet to minimise the amount of atmospheric moisture entering the glue. Hopefully this will slow down the cure rate and won't produce the big bubbles we normally get. Will have to check tomorrow to see how it went.

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NSWRA Open Day

NSWRA is having an open day this month on the 22nd November at Toongabbie East Primary School. We will have a water rocket stand there along with the pyro guys. If you are interested in any form of rocketry why not come along? See the flyer below for details:
We are going to be busy over the next few weeks to get the rockets ready for the open day. We want to bring the Polaron rocket with the drop away boosters, the new bigger Acceleron booster, and the new FTC rocket with us. We'll also bring along some of the other smaller rockets.

We have had a bit of a break from water rocket development this last month due to other family commitments, but are now back and should be updating the main site and blog more frequently.

I've also been continuing work on the next iteration of the flight computer (V1.6). The software has had a bit of a revamp to make it easier for the rocketeer. I'm also in the process of laying out a new smaller double sided PCB for it. We've located a local PCB manufacturer with very reasonable rates for the boards so we will likely have around 20 of them made, most of which will go up for sale assembled as was with V1.5. I've switched from using an old version of Protel for the schematic and PCB layout to Eagle which is much more advanced and certainly has some very neat features. Luckily the PCB manufacturer can take the Eagle files directly which greatly simplifies the process.
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