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.

Sunday, February 21, 2010

Acceleron V rebuild

We've made good progress this week in getting Acceleron V back on the launch pad. Early in the week we tested the new narrow nozzle seals to make sure they will hold up to the pressure. This was also a pressure test of the booster side of the launcher. During assembly we noticed that one of the nozzle seals was distorting too much when the bottle was tightened. So dad machined up a new nozzle seal cutter that was a little wider and we made 3 new nozzle seals out of harder rubber. These worked well during assembly and in the pressure test.

Pressure testing the new nozzle seals. You can see the fog in the upper bottles as we let the pressure out.

On Friday we pressure tested the sustainer release mechanism and air supply. During the test we noticed that there was a very minor leak (1 or 2 drops per second) in the release head. On closer inspection it looked like there were a couple of small vertical grooves in the o-ring seat. So we spent today replacing the Gardena release mechanism with a new one. We are letting the epoxy fully cure before doing another test.

We spent the rest of today re-assembling Acceleron back to its normal configuration,.

Attaching the fins with the use of a fin alignment jig.

There are still lots of little jobs to do on the rocket, but it's good to see it back together again. We will do an integration pressure check to around 60psi to make sure there are no leaks in the Tornado couplings without putting too much stress on the entire rocket.

Next major milestones include a re-assembly of the sustainer. Depending on our progress schedule we may fly it at this weeks NSWRA launch day to flight qualify it before it gets used with the Acceleron booster.


Unknown said...

Hi George - how did you make your newest connector (bottle to bottle) how did you cut the threads? what size and type of thread? Thanks for all of the great information on you web site and blog- Jeff

George Katz said...

Hi Jeff,

The tornado coupling is made from a standard 3/4" BSP polypropylene socket you can get from irrigation shops. We put it on the lathe and cut the new thread to match the bottle. I don't have the thread details with me at the moment, and can't recall the numbers off the top of my head since it's over a year since we made them. But I can dig up the tech drawings if you like. We also machine o-ring seats in the ends so that the BS-119 o-rings sit snuggly against the first ridge on the bottles.


- George

Daniel Collins said...

Wow, your hobby is certainly advancing :-). Been watching you guys for a long time now. I am still struggling to find some decent vertical guides for the bottles, let along triple bottle launchers...

George Katz said...

Hi Daniel,

Thanks for following along. Aluminium tube works very well as guide rail material. It doesn't corrode, it's light to carry around and is available in pretty much all hardware stores. :)

- George

Daniel Collins said...

I guess I need to get some money together, and go for it :-). I'm keen for single bottle radii at the moment, so the launch mechanism shouldn't be difficult (bought an aluminium garden hose quick connect). My favourite part is making the launch computers... One thing I see you haven't though of is reducing weight by stripping out extra parts. I have an idea to have a small flight computer that has some outputs for servos, and launch sensor, and a 3.5mm stereo socket for programming it from an external box. You can set it up with a super capacitor, so that the main device charges the rocket. Just something to think about :-)

George Katz said...

Hi Daniel,

Sounds good with the flight computer design and the use of super capacitors. Being able to configure the flight computer in the field is very important as things often change, or you want to try something different.

I am in the process of switching from the 9V batteries and CR123As to tiny Li-Po batteries that weigh about 4 grams. We should be able to get a full day's flying on one charge.

As far as weight goes, we really haven't been concentrating on that too much. Most of the rockets we build are only for fun experiments, and so the weight is not too critical like would be for record attempts. For us modularity and ease of manufacture are more important.

Daniel Collins said...

Hey George,

I'm using the ATtiny2313 (Kind of like the AVR equivalent to you PIC) as the in-flight computer. It can run off 2.7v to 5.5v. Nokia cellphone batteries being 3.7v. I've got a few of them now, great for projects like this.

A problem I have is with parachute size. How fast do I want the rocket to fall? I can make a big chute, but it takes up lots of space, and is pretty heavy. Maybe I need to use thinner bags...

George Katz said...

Hi Daniel,

Sounds good running of a single 3.7V cell. It makes power requirements much easier. Although I am not sure you will be able to also power a servo from that. Only way to know is try. Unless you are not using a servo of course.

The size of your chute will depend on how fast you want the rocket to fall, but 3-5m/s is normal. Here is a good resource to work it out:

Faster descent = less drift, slower descent = more gentle on the rocket.