This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Saturday, February 21, 2009

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:

Thursday, February 12, 2009

Flight Computer V1.6 Details

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

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


Sunday, February 08, 2009

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.


Saturday, February 07, 2009

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.


Wednesday, February 04, 2009

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.