Posts Tagged ‘bottle’


Updates – Variable Height Launcher

Due to the extra length of our new “Green Hornet” water rocket car, we need to do some updates to the launcher. The updates needed are

– Lengthen the distance between the quick release and the launcher
– Make the quick release height above the ground variable

We have different rear wheels on the Green Hornet which has changed the height of the nozzle above the ground. The old launcher was setup with the quick release at a specific height to match the rocket car. So as we try these wheels and experiment with other lighter wheels, we need to be able to quickly adjust the height of the quick release.  Its important the quick release mates well with the rocket nozzle otherwise it will leak under pressure

Launcher Mated to the Green Hornet

As can be seen from the pic above the length of the hose to the quick release has been increased by about 30%. There is plenty of space between the new rear wheels and the launcher. The hose is kept rigid by being cable tied to a steel rod under the pipe.

Launcher hose strapped to steel rod

The steel rod is bolted to the movable section of the launcher.  The heads of two hex bolts (ready for 4 when I find another 2 bolts) run in metal channels (old curtain rod) up the face of the splash guard. Wingnuts on the bolts enable the movable section to be positioned and tightened at the location required.

Closeup of movable section of launcher

A hole was drilled in the movable section and a channel cut out of the splash guard for the launch string to be fitted. The launch string will work freely at any height.

Launch string groove

Here are a few more pics of the launcher mated to the “Green Hornet”

Launcher mated to rocket car

Another pic

Close up of mated quick release connection

The launcher and the new rocket car are finally ready for a launch day. We also have three reinforced bottles almost ready to swap in if hydrostatic testing goes well.

Posted by on July 4th, 2010 Comments Off

How to make a 2L Reinforced Bottle

We are trialing using 2L reinforced bottles to power the rocket car. Here is a brief overview of our process.

We start with 3 bottles

- 1 x 2L bottle
– 2 x 2.25L bottles (although 2L would probably suffice)

Start with 3 bottles

The 2 x 2.25L bottles are cut so that one will go over over the bottom of the 2L bottle and one will go over the top. There is an amount of overlap as well where the top and bottom sections overlap to be 3 layers thick.

Cut out sections + 2L Bottle

Close up of the 2 cut sections

The next step is to shrink slightly the 2L bottle. A big pot is required which can be filled to a depth of 3/4 of the bottle + have spare volume so no hot water splashes out when the bottle is inserted. Be careful of this, make sure the pot is big enough.

Bring the pot of water up to about 75 degrees, you can test this by quickly inserting the bottle 2 seconds or so and see if it shrinks slightly. Dont get the water too hot or the bottle will shrink to fast and deform. Once the water is the correct temperate insert the bottle for 2  seconds and check how much the bottle shrinks. Its better to do it a few times rather than have the bottle too long in the water and deform.

Submerge the bottle to past 1/2 way until the bottom section shrinks, then turn the bottle around and do the top as well. Be very careful with the top, you dont want the spout deforming.  What you should end up with is a bottle that is slightly smaller over the entire area (except the bottle throat and cap section).

The next step is to fit the other two sections. Start with the bottom section first, you will find that as its a close fit it wont slide on easily due to the air trapped in the bottom section.  There are a couple of ways around this. One is to use a wooden skewer or similar and push it between the two bottles so the air trapped in the cutout bottom section can get out, or you can drill a small hole in the base of the bottom cutout (not the 2L) bottle and air will get out this way. As we are going to fit a Robinson coupling anyway this hole wont weaken the second bottle.

You can put a bit of PL premium between the two bottoms of the bottles to hold them together but this is optional.

Once the bottom section is on, put the top section over the top of the 2L bottle, we slide the top section underneath the overlapping bottom section. TO do this its easier if you have a wooden skewer and run it around the bottle while you push the top section in, then just push until the top section is in place. You will find that once in place they really dont move. You can add a strapping of fibre reinforced tape if you wish.

Here is a pic of the bottle when finished. Its has already had a robinson coupling added to it.

Completed Reinforced Bottle - Robinson coupling added

If you look carefully you can see the slightly shrunken inner bottle.

Posted by on June 26th, 2010 1 Comment

Reinforced Bottle Testing – 2L@180psi

Work has commenced on reinforcing 2L bottles to increase thrust on the water rocket car.

The first attempt to make a 2L reinforced bottle uses
– 1 x 2L bottle (slightly shrunk)
– 2 x 2.25L bottles

The 2L and 2.25L bottles have the same diameter, the 2.25L is slightly taller though. The  2L bottle was slightly shrunk in hot water to reduce its diameter so the 2.25L would slide over the top of it. One of the 2.25L bottles had the top 1/3 cut off. The other 2.25L bottle had the bottom 1/3 and the the bottle throat section removed.

Then 2.25L bottle without the top was then slid over the bottom section of the 2L carefully lining up the claws at the base. The second 2.25L we had to cut a bit more of the throat away to fit it over the 2L bottle throat flange (for want of a better word). The 2 x 2.25L bottles overlap a little in the middle. It was then just taped this down with fibre reinforced tape to hold all the sections in place

Standard 2L (left) and 2L reinforced (right) bottles.

Reinforced bottle on its side

The bottle was then ready to be hydrostatically tested. A few modifications for safety were made (due to the higher test pressures) to the air hose to hold the hose and connectors in place in case the air hose exploded. Each separate section of hose was cable tied to a brick

Pump to airhose connection hold-down

Airhose to abort valve hold-down

The bottle itself was placed in a milk crate with a 20L water container (full) placed on top to hold it down in case the bottle exploded as a safety cage.

Bottle Testing Cage

There is a valve in the female gardena connector that will close off the airhose if it has pressure in the line but no bottle on the open end. This makes it easy to test the air hose itself for leaks. Safety glasses were put on and the air hose (no bottle) was pressure tested up to 180psi with no leaks. This is the pressure we decided we wont test past until the airhose, connectors and PVC abort valve are replaced with stronger components.

Safety glasses were put on again and the reinforced bottle was filled with water and pressurized to 180psi. There were a few drips from the nozzle (only hand tightened) but the bottle held the pressure fine.

Reinforced bottle hydrostatic test to 180psi

The next version of the reinforced bottle we will grind of the flange of the 2L so that the throat section is more reinforced and use PL Premium to glue the bottle sections together.

The test was very successful, this is the highest pressure we have pressurized a bottle to. It seemed the reinforced bottle could take a lot more pressure before bursting as there was minimal (visually) stretching of the bottle. We are working on replacing the components for the air delivery and will try a further hydrostatic test once these are in place.

Posted by on June 2nd, 2010 Comments Off

Water Rocket Car MkXI – The Green Hornet

A lot of work has gone into reworking the rear of the rocket car and reducing weight as much as possible. The modifications include
– New rear chassis of the car
– Low friction (Lighter) rear wheels
– Rear wheels much further back from the nozzle – reduce thrust steering
– New Rear fin design – larger wing surface
– New nozzle alignment guide
– New electronics bay

The following parts were also modified to reduce weight
– Chassis
– Nosecone
– Rear wheels
– Rear Fins
– Electronics bay
– Rear Alignment guide

As this will probably be the last major change to this chassis before we build a new one, we also gave it a nice paint-job and christened it “The Green Hornet”

Rear of the Car
The Rear section of the chassis was replaced with a new design that was lighter, had the wheels much further behind the nozzle, allowed for the new 45 degree wing design as well as a space to try a new additional nozzle / air amplifier (not pictured yet). The rear section is only glued to the front section of the chassis with wood glue. It is extremely strong, as we found out when pulling off the older rear section of chassis which was also glued on.

Rear of the Car

Rear of the Car

The rear wheels have had the rubber removed to both lighten the rear wheels and reduce friction with the road. The theory is to minimize the force required to straighten the car, ie: move the rear of the car back into alignment with the front of the car. We are trying to make it behave more like a rocket than a car as per our previous down-force rear wing design which tried to reduce thrust streering by maximizing rear grip. Testing will tell if this configuration will work or not.

The nozzle alignment guide has been lightened but still ensures the nozzle points directly out the back of the car.

Rear Fins
The new rear fins are made of corrugated plastic to reduce weight. A set was made from thin plywood first but they were to heavy and too flexible, the corrugated plastic ones with the corrugations running from the centre to the tip were actually stronger and lighter. A 45 degree piece of wood was glued to the fin using PL Premium. The wood is screwed to the chassis to secure the fins.

Rear 45 degree Fins

Front of the Car
Changes here include a new electronics bay setup with a flip top section that opens up to allow access to the servo and steering rod connections. The on/off switch has also been moved to a better location now protected within the nosecone.

New Electronics Bay & R/C Steering

The nosecone has also been lightened and of course painted green :) A hoel to access the on/off switch


Nose Cone

Chassis Weight Reduction
The new chassis is 1.40m long but a lot lighter than the previous chassis.The jigsaw and hole saw were put to good use to lighten the chassis as much as practical while still retaining its strength. Being painted white, it is easy to see the holes cut out of the chassis. Triangles were used where possible for cross-members to retain strength.

Chassis in white

Front Alignment Guide
The front alignment guide between the first and second bottle was left as is. This is the section where the rocket itself is imparting most of the force to propel the rocket car forward, without it the rocket will shoot off and leave the car where it is. So it was thought to best leave this with a larger surface area rather than reduce it.

More Pics of the Car

View from the front

View from the Rear

Rear Wheels - No rubber

Weight Saving
The car pictured above weighs in at 2.560kg which, while considerably more than a water rocket, is far below the previous version of the car which weighed in at 4.5kg. This weight reduction should improve both the maximum speed of the car as well as the distance traveled .. hopefully.

Additional Work
The new “additional nozzle / air amplifier” will be a second nozzle behind the main nozzle. The idea is to try to push in some of the surrounding air into the exhaust plume using a difference in air pressure between the exhaust plume and the air rushing past the rocket car. This will sit in the area, behind the main nozzle and in between the rear fins. It will be removable so we can test the car with it and without it.

We also need to strap the bottles down to the chassis and do a hydrostatic test to make sure we have allowed enough space for the bottles to expand under pressure with the new alignment guide.

We need to modify the launcher to increase the length of the hose from the launcher to the female gardena connector, this is due to the extra length added to the car and the nozzle now being further away from the rear wheels

Posted by on May 20th, 2010 Comments Off