Archive for July, 2010

 

New Image Display Plugin

We have installed a new image display viewer on the website called lightview.  It quite a nice way to view images without going to a separate page. All the images on every  page are clickable to pop up a bigger version. Enjoy

Posted by on July 28th, 2010 2 Comments

Water Rocket Mist Attachment – Static Test

An interesting development we saw on www.wra2.org from Jelo and Thunderrockets was a device called a mist rocket. This is an alternate method of mixing the air and water into the exhaust plume which produces a single air/water thrust and not the normal water then air pulse of a standard water rocket. Also when flown vertically there was a distinctive jet sound.

We though we would give this a try for our water rocket car.

The design uses a PVC pipe to funnel water from the second bottle to the nozzle. The air pressure in the top and bottle bottles are equal. The air in the top bottle pushes the water down the pipe and the air pressure in the bottom bottle forces air through two (2) small holes to mix air with the water just prior to escaping from the nozzle.

This is how we built it and tested it.

First we purchased some 20mm electrical conduit and a conduit cap. The 20mm conduit just fits in the 22mm bottle throat. A 10mm hole is drilled in the centre of the conduit cap and a 10mm internal diameter (ID) nut from our robinson couplings is carefully glued (with 24hr araldite) into the base of the cap, making sure no glue gets on the threads.

20mm Conduit Cap with 10mm ID nut - no glue yet

The conduit cap is then glued (24hr araldite again) to a section of 20mm conduit (longer than the bottle at this stage) and left for 2-3 days to set properly. Once this is set, this section should screw easily onto a standard 10mm robinson coupling thread.

Conduit connected to threaded rod (robinson coupling rod)

The next step is to cut the conduit so that it fits just inside the nozzle cap. The section is screwed onto the robinson coupling between two bottles then marked, unscrewed again and cut to size. The conduit shouldn’t protrude past the bottle lip as this will cause the bottle lip not to seat properly against the rubber washer in the nozzle and the bottle wont hold pressure.

Conduit cut to size of bottle

The conduit section then needs 2 holes drilled near the base of the rod. we used 6mm holes, these are to let air from the bottom bottle mix with water from the top, also if any water does get in the bottom bottle it allows it to escape.

Conduit section with cap and 2 holes drilled near the base

The completed conduit (now referred to as mist attachment) is then inserted into the bottle and screwed onto the robinson coupling. Note that about 10mm of thread was needed on the threaded rod to catch on the nut threads.

Robinson coupling ready for mist attachment

Mist attachment connected to robinson coupling

The the nozzle is screwed into place and its ready to test / launch. Here is the pic ready to test

2 Bottles with robinson coupling and mist attachment - Ready to test

The handy thing with this attachment is that it can be added and removed quite easily for test or launch.


Mist Attachment Test

The test we conducted was a vertical static test with 1L of water (no foam) and 100psi. The bottles used are 2.25L bottles. We were interested to see the following

– If we could reproduce the jet sound that thunderrockets produced on launch
– Examine the exhaust plume to see if it generate a good air / water mix
– Examine if there was any distinct air pulse after the water was ejected from the bottles

We did find that filling the top bottle a little more challenging to ensure water didn’t get in the bottom bottle. We used a small section of hose connected to a funnel to get the water past the 2 holes in the mist attachment, then gently pumped the top bottle.  Here is a video of the test

Conclusion

– We didn’t get the jet sound, even after 2 separate static tests – its a possibility that the rocket needs to be flying through the air to generate the sound, or possibly the holes were too big.
– The exhaust plume definitely had a good mix of water and air and produced a spray similar to a foam launch
– There was no distinct air pulse after the water was ejected
– An interesting observation was that there was minimal (a small amount) splash back in the bottle at the end of the thrust phase.

We will try this test again in a horizontal configuration to suit our water rocket car

Posted by on July 27th, 2010 5 Comments

New Google Translation Plugin

This is our second attempt at providing the website in multiple languages. We are now using a simple plugin in the right sidebar which will translate the HHWRSA web pages to the language of your choice. Simply use the pulldown menu to choose the language you need.

This plugin doesnt cache the pages in multiple languages on our webserver, just creates the translation as you need it.

Enjoy :)

Posted by on July 22nd, 2010 1 Comment

Launch Day Damage & Onboard Camera

We are not used to crashing on our launch days anymore, so we were a bit surprised to see the R/C not responding during some testing after the last launch day. The heavier crash was on the front wheels, so we were hoping it wasn’t the servo that was damaged.

Fortunately after some testing with the multimeter we found one of the wires on the pole of the power switch had snapped off under its insulation and wasnt making contact. Also one of the hinge mounts for the electronic bay support had broken away from its mount when we took it apart to find the wiring problem.

Wire Broken off power switch

A quick resolder fixed the wire back onto the switch pole and a 5min epoxy glue fixed the broken mount. All working again :)

We have been wanting to show some onboard video from the water rocket car for quite a while. We will probably order a MD-80 clone or similar to what George at aircommand has had good results with, but in the meantime we will decided to just use a cheap camera we have floating around. If it gets smashed then no great loss. Only downside is it weights 180grams :(

Camera Mounted facing rearwards

Yes we know its not terribly aerodynamic, but at least its a start in the right direction. The camera is bolted down using its tripod mount and a screw and nut (hidden in the pic). We will improve the camera setup with the next version, to make it lighter and more aerodynamic. This will do for the moment to show some onboard video at our next launch day :)


Posted by on July 20th, 2010 Comments Off