Archive for November, 2008

 

Hydrostatic Silencer

Regulars to the blog would know that I do a lot of testing / building late at night. One thing I like to do prior to launch is a pressure test of the wrockets pressure bottles, especially where there are multiple bottles and robinson couplings.  Even though these are not burst tests, it is loud when the abort valve is opened, not to mention spraying a lot of water around.

We needed a solution that would keep the place kind of dry and let us test at night without waking the neighbors. We had some good suggestions from the water rocketeers on the Water Rocket Forum and came up with the Hydrostatic Silencer

Our launcher has a gardena style quick release (that has a one way valve in it) as well as a abort valve. Here is the setup

Hydrostatic test setup

Hydrostatic test setup

The launcher itself is not used, one side of the quick release plugs straight to the pressure bottle being tested (this opens the small 1 way valve in the gardena), the abort valvue has had an extension piece added (which is removed when launching) on the output of the abort valve and goes into a bucket of water

Abort Valve and Silencer attachment

Abort Valve and Silencer attachment

The attachment is 13mm black poly hose which is quite rigid and strong, the end was sealed up with reinforced tape and the end 10cm perforated with approx fifty (50) small 3mm holes.

Perforated end of hoose extension

Perforated end of hose extension

Here is the extension by itself. I cable tied some metal to the perforated end to make it sink in the bucket of water

Silencer extension by itself

Silencer extension by itself

threaded end is a 15mm screw fitting to the abort valve

threaded end is a 15mm screw fitting to the abort valve

Here is the video of it in action, you need to make sure you have your audio on to hear what it sounds like.

Its makes a lot less noise. I just have a piece of wood over the top of the bucket to stop the water splashing out, but I will invest in a new bucket with a lid :)

It works well for our purposes. Now on to testing more bottles :)

Posted by on November 14th, 2008 Comments Off

Launch Rail

Launch Rail
After the ground hugging cruise missile on our last launch day due to wind knocking the wrocket off the launcher, we decided for safety’s sake to install a launch rail prior to our next launch day.  We looked at the different options available and decided on a launch rail and launch lugs for the wrockets.

On the positive side this launch rail configuration will

  • ensure the wrocket can site vertical on the launcher if we get gusts of wind prior to launch
  • ensure we get vertical off the pad
  • with redundant lugs on the wrocket ensure we still get off the pad vertical even with multiple lug failures

On the negative side

  • this configuration will cause extra drag on one side of the wrocket due to the lugs. How this effects flight we will have to see on our next launch day

We decided to go with a curtain rod as it was practically perfect for our needs and also came with the lugs already supplied (normally used to hang the curtains). here are some pics

Curtain Rail

Curtain Rail

Rail and Lugs

Rail and Lugs

I had seen these in a local shop and they were about $30 which was a bit steep so I kept looking. Luckily this week is a council cleanup here so everyone puts out their old junk to be picked up and thrown out. I spotted exactly what I needed when driving home one day not 500m from my place. I turned around and picked up 2 x 1.8m rails with lugs attached …. recycling at its finest .. perfect ! As a bonus I found that these actually had another sleeve inside them which allows it to extend up to 2.8m which is more than enough.

The rail is attached to a solid “L” bracket with cable ties (temporary but strong enough to test with) vertically and this is then attached to the base with 2 screws with wing nuts. This allows it to be removed for transport then quickly reattached. At the moment as we are using the 1.25L as our standard bottles the fixed rail location is fine.

Launch Rail Attachment

Launch Rail Attachment

To get it to fit we had to move the support pole off centre a little. Here is a pic showing the rails full height on the launcher

Launcher and Launch Rail

Launcher and Launch Rail

View looking down the rail

View looking down the rail

Lugs
Next step was to modify the existing curtail rail lugs to fit on the wrocket. These were just cut and filed. Below the original curtain lug is on the right, the middle and left are ones that have been cut and ready to stick onto the wrocket.

Lugs

Lugs

These were stuck onto the wrocket body modules with PL Premium (this stuff is brilliant) and left to dry for 24hrs.

2 Lugs on bottom bottle

2 Lugs on bottom bottle

Lugs stuck to other bottlles incl nosecone

Lugs stuck to other bottles incl nosecone

The other bottles had one (1) lug each and the dummy nosecone has 1 as well. The parachute modules dont have one to reduce the chance of an elastic band getting caught up on one.

Ready to Fly
Here are H2 and (the new) H3 wrockets with their lugs glued on and aligned. H3 has the bigger Removable Fin Assembly as it will soon have another pressure bottle added.

H2 & H3

H2 & H3

Here is H3 on the launcher with the lugs in the rail

H3 on the launcher

H3 on the launcher

Initial Testing
The initial test were done with 30psi (no water) just to make sure the bottle would come off the launcher properly.

Test Config

Test Config

The launch rail worked perfectly with no hangups. This was tested a few times with perfect results. Next test will be the launch day with H2 & H3 in action.

Posted by on November 10th, 2008 1 Comment

Tomy Timer Mounting Modification

We are working to improve the reliability of the tomy timer. One of the things we are trying to improve is the way its mounted in the parachute modules. The back of the timer has lots of holes in it, and getting even the smallest bit of glue on one of these slows up or completely stops the timer. To correct it we have to remove it and jab at the small holes with a needle to free the glue up to get it moving again.

Another downside of putting glue on the back of the timer is that you can only use a little bit in the places where there are no small holes, and it doesn’t take much to break off from the mounting on a crash or heavy landing.

One method we are looking at is using the timer mount that comes with the toy itself. This in effect is the base of the toy, but it provides a clip mechanism and is molded to keep the timer in the right place. Here is a pic with just the top of the toy removed.

Tomy Toy with top and front wheels removed (top)

Tomy Toy with top and front wheels removed (top)

Tomy Toy with top and front wheels removed (side)

Tomy Toy with top and front wheels removed (side)

Here is the piece with the tomy timer removed

Timer Holder (top)

Timer Holder (top)

Tomy Holder (side)

Tomy Holder (side)

The idea is to mount this timer holder to the parachute module structure instead of the actual timer, then the timer sits quite sturdily inside the holder and clips in with the two clips that wrap around it.

To get a good attachment the little side wings are removed with a sharp knife (carefully) and sanded smooth. This provides the entire surface area of the edge of the holder to be stuck to the structure. Here is the side after being sanded

Timer Holder Sanded

Timer Holder Sanded (side)

Timer Holder Sanded (top)

Timer Holder Sanded (top)

Here is the tomy timer with the wheels removed and the winder attached placed in the holder.

Tomy Timer in Holder

Tomy Timer in Holder

Tomy Timer in Holder

Tomy Timer in Holder

Once I have it mounted in the parachute module I will add some pics here

Posted by on November 4th, 2008 Comments Off

Bigger Removable Fin Assembly

The rockets we are building are starting to get longer and heavier and so for 3 pressure bottle and higher wrockets we are probably going to need bigger fins to put the centre of pressure where we want it for stable flight.

We are very happy with the trapezoidal fin shape so we have scaled this design up approx 50% to make the fins based on a 12cm side instead of 8.5cm side. Also the length of the RFA body we have extended slightly so that the nozzle when attached to the rocket doesnt extend past the RFA body. This also makes it easier to stand up when not flying.

The build was very much the same as the previous RFA build procedure.  The fins were cut out in a trapezoidal shape

Bigger RFA Cutout

Bigger RFA Cutout

Notice the channels of the corrugated plastic are in the direction of the airflow when in flight. Leaving these open seems to work well.

Here are the three fins and the 6 support attachments. The support attachments are 10cm long and 8 channels wide.

RFA Parts

RFA Parts

Instead of using metal wire to attach the fins to the RFA body, this time we have used PL Premium glue. This is the water rocketeers glue of choice and was very easy to work with. We will see how it goes during flight but I am quite confident it wont come off. The RFA body was cleaned with Mineral Turpentine, then washed with soap and water to give a nice clean finish for the glue to adhere to.

Here is the finished RFA sitting on a bottle drying.

Bigger RFA finished

Bigger RFA finished

Bigger RFA Top View

Bigger RFA Top View

The unit weighs in at a hefty 45grams

Posted by on November 3rd, 2008 Comments Off