Archive for January, 2011

 

Howto build a Launch Cage with Guide-rail – Part 3

This is the final part of the launch cage construction posts, it  covers the addition of the mesh, the access for the air hose as well as final adjustments. We learnt a lot about applying mesh and have included tips below which should speed up the time to do this task for others.

Attaching the Mesh
The mesh that we used is a zinc coated welded steel mesh made by Whites Wires here in Australia. Its has a 6.5mm (1/4″) square aperture and a 0.6mm wire diameter. This mesh  is usually used for  snake and mouse protection on aviaries.  The welded mesh provides more rigidity to the mesh than twisted wire mesh such as chicken wire.

Closeup of Mesh

TIP 1 : SAFETY SAFETY SAFETY – Anytime you are working with mesh or wire its very very important to wear wraparound  eye protection and gloves  while handling the wire and mesh.  Wire strands can easily get into your eye and you dont get a second chance with your vision. Also the mesh is very sharp when cut so gloves are needed !!!!!!

The initial plan was to use wire to wrap the mesh to the frame. So first a section of the wire was cut to size for one side. This took quite a while with wire cutters, cutting each wire individually.

TIP 2:  USE A ANGLE GRINDER TO CUT THE MESH – Use an angle grinder to cut the mesh. It cuts through it like butter and also trims off the sharp edges all in one go.

Once the wire was cut to size it was placed against the frame. Initially the mesh was cut right up to the edge of the frame. As the frame is 35mm wide, it doesnt need to go all the way to the frames edge as it will expose the edges. Its safer to cut the mesh about 10mm away from the edge.

TIP 3: CUT THE MESH 10mm SHORT OF THE FRAME EDGE to prevent cutting your leg as you walk past it once its on.

The mesh was trimmed then using wire it was strapped to the frame by wrapping the wire around the frame and through the mesh. Basically sewing it to the frame. While this did work and the mesh was tight against the frame, it took about an hour to do one side and left a lot of the sharp ends of the strapped wire exposed .

There had to be a better way….  We did  some research on how  mesh was added to the frames of aviaries. The answer it turned out was universal and quite simple ….  tek-screws !

Tek Screw with Hex Nut

A tek screw has a self drilling point and the ones we used had a hex bolt head that held the mesh tight against the frame. We also used a magnetic hex Tek bit for the power drill which made installing these very fast.

TIP 4: USE TEK SCREWS TO ATTACH THE MESH TO THE FRAME

Once the wire wrapping was removed, the same side section was attached with Tek screws in about 5 minutes. Here is a closeup of the tek screws holding down a mesh section.

Closeup of tek screws holding down sections of mesh

In all we used about 125 tek screws to attach all of the mesh to the frame. Where the mesh needed to be trimmed it was done with the wire cutters but in most cases it was cut to size with the angle grinder before being put onto the frame.

Securing the Access Door
The access door is covered with mesh from the inside, it uses the two wooden stoppers to stop the door falling into the cage and the  sliding bolt to hold the door in place.

Sliding latch on access door

Air Hose Connection
The air hose connection to the launcher is fed through a small hole cut in the mesh. Access  to connect the airhose to the launcher is via the access door. Here is the airhose in place and the accessdoor open.

Airhose connected to launcher with access door open

Final Adjustments
Finally, here is the water rocket car in place on the rail and attached to the launcher. Some small adjustments on the lugs were made to get the exact height correct. Several manually powered launchers were made to check all was working satisfactorily. Some grease will be applied to the rail before a powered test is made. Here are some pics of the final cage.

Finished Cage - Side View

Finished Cage - Rear View

Water Rocket Car attached to the launcher and guiderail

One tip we found after we had already applied the mesh was to paint the mesh itself black. This virtually makes it dissapear to the eye and is usually performed to make viewing birds easier. With the white frame we have, we probably wont bother trying to paint the mesh black :)

Only thing left to do now is some powered tests of the rail and the cage. Hopefully we will get this done shortly, then head to the launch site to try to set some records :)

Posted by on January 25th, 2011 Comments Off

Howto build a Launch Cage with Guide-rail – Part 2

Guide Rail
As we realized in the design stage a guide-rail is necessary to ensure the water rocket car clears the cage without hitting the sides on launch. We use a split tail design on our water rocket car, so for us the best spot to attach the guide-rail to the car is down the centre.

The guide-rail itself is  a metal curtain rod which we have used previously as a vertical launch rail for our vertical water rockets. It also happened to be about 1.5m in length which was a perfect length.

To attach the guide-rail to the cage we suspended a section of timber from the top of the cage along the centre. It was important to make sure this piece was perfectly horizontally  level, otherwise the car may bind up in the rail on launch.

Guide-rail attachment suspended from the top of the launch cage

there is a bit of clearance between the car  to attach the rail itself as can be seen from this test fit picture.

Test fit and clearance of rocket car to rail

The rail was then attached to the suspension section with some blocks to get the rail closer to the car.

Guide-rail attached to suspension section

Here is the car in place under the rail. The alignment looks pretty straight.

Car in place under the rail

Car Rail Lug Attachments
Next the lugs needed to be made up and attached to the car. As the bottles need to be able to be removed from the car, we made up some U shaped attachments. One is placed over the nozzle and the other over the first and second bottle gap. These are spaced to allow the bottles to expand without pressing too hard against either of  them and possibly rupturing or bending the lug attachment.

Guide-rail lugs and attachments

Large screw heads were the right shape and size to use as lugs to slide down the guide- rail, so appropriate sized screws were secured into the attachments. The attachments are secured into the chassis from underneath. Using screws as lugs allows for the height to be  adjusted by turning the screw in or out to fit in the rail correctly.

The U shaped attachments were painted green to match the rest of the car.

PaintJob
The cage was given a coat (or 2 ) of paint to smarten it up a bit. The launch rail attachment was painted green to keep with the Green Hornet theme :)

A coat of paint :)

The last part of this 3 part posting will cover the attachment of the wire mesh, test fitting the attachment lugs and adding the access to the launchers airhose.

Posted by on January 24th, 2011 Comments Off

Howto build a Launch Cage with Guide-rail – Part 1

We intend on competing in the WRA water rocket dragster class, which is a new water rocket class dedicated to water rocket cars. In order to compete and submit an entry for a record, the cars pressure vessel needs to be enclosed within a wire mesh cage as part of the safety rules. This can either be on the car itself or a separate launch cage. We opted for a separate launch cage. The launch cage ensures any shrapnel from a pressure vessel that ruptures on the launcher stays within the enclosed cage and away from spectators and launchees.

This three part post describes how we designed and built our cage. Whilst of course this is not the only way it can be done, there are some things we learned along the way which may assist others who want to build a similar cage.

The Design
The design had some basic requirements that we started with

  • The entire pressure vessel of the car needed to fit within the cage
  • We needed to be able to transport our cage to our launch sites
  • Not too heavy
  • Comply with the WRA safety rules – mesh size etc
  • Ensure it would be strong and arrest shrapnel

So we started with some basic measurements – the cage would need to be 155cm long to cover the entire car + launcher in the cage. For the width we quickly determined that we would need some leeway either side of the rear wings otherwise the wings could get caught up in the cage on launch. We decided to leave 10cm (4″) either side of the wings to the edge of the cage. For the height we left 20cm (8″) of space as well.

It was fairly obvious at this stage that a launch rail would be required to keep the car straight leaving the cage so it would not get caught up in the cage itself whilst launching.  Also it seemed we needed an access door on top to allow the water rocket car to be mated to the launcher. It was going to be to far to reach in from the front of the cage to do it. We now had our  basic layout for the cage. This is the sketched up plans we used to build the cage.

Basic Design - Launch Cage + Guide Rail

Building the Frame
I tend to like to work with wood as its more forgiving of mistakes and changes. We wanted to keep the weight down but ensure the wood we used was still strong enough not to break or split if we had a rupture. We had some leftover 70mm x 18mm pine from a previous project and decided we would use that for the frame. The 70mm was a bit of an overkill so we decided to split it down the middle to make 35mm x 18mm sections. This also doubled the amount of timber we had available to use. It was a bit tedious splitting all the timber with a jigsaw but the end result was fine. Im guessing we used about 16m of the 35mmx18mm timber all up.

Construction started by making the top section and the two sides separately, the joins are nailed and glued

Basic Frame, top section (left) and one of the sides (centre)

Basic Frame, top section (left) and one of the sides (centre)

The sides were then attached to the top section and glued in place, the clamps held everything in place while the glue dried

Sides and Top section nailed and glued together

Sides and Top section nailed and glued together

The next section was the access door. This is 30cm x 50cm in size and adequate enough to reach into the cage. It is nailed and glued and attached to the frame by 2 hinges. It stops flush with the top section of the cage by two stoppers.

Access Door - Closed position

Access Door - Open position

Next we needed a way to connect the launcher without having to physically connect it to the launcher or  screw it to the cage for a launch. Even with our 20kg water ballast on the launcher, the launcher itself still recoils backwards ~10cm (4″) on launch. We didnt want the launcher ripping the mesh of the cage when it recoiled, so we made a wooden section in the cage that fits over the launcher to connect them without impeding the launchers function. When the launcher recoils on launch it will drag the entire cage with it and not stretch the mesh section of the cage, the cage can also easily be lifted off and separated from the launcher.

Launcher Attachment

Launcher Attached to Cage

Here is the water rocket car in place to check out everything fits and there is enough space for the car to clear the sides of the cage as well as test the access door to the coupling of  the car and the launcher.

Test Fit of Water rocket car in the cage

Test Fit of car / launcher connection through access door

View from behind the launcher

This is the end of the frame build. The next post will cover the guide rail and additions to the water rocket car to connect to the guide rail.

Posted by on January 22nd, 2011 2 Comments

Water Rocket Car Cameras

We are going to try a couple of different cameras to reduce weight on the water rocket car.

We have ordered an MD80 clone camera which is very popular in the  rocket and R/C communities as well as a cigarette lighter camera. Both support SDHC MicroSD memory cards so we purchased a reputable 4GB card which will give us hours of recording time.  The lighter camera arrived first so we will review this one first.

Lighter Camera
The lighter camera looks just like a normal cigarette lighter but it is a hidden video camera with audio inside.  Its main features are:-

  • Its very light at 16 grams
  • Its camera lens is on the end of the lighter, so can be streamlined along bottles
  • Built-in 220mAh rechargeable lithium battery that charges via USB
  • Resolution of taking video is 720*480
  • Resolution of taking photo is 1280*1024
  • Support Micro SD card Max to 8G
  • Lens: 2.0 Mega CMOS
  • The video adopts motion JPEG, records and saves it as AVI files
  • USB interface : USB1.1/2.0

Here are some pictures of the lighter camera

Lighter Camera

This camera is fairly easy to use once you know what the sequence of lights means. As all modes are activated with the one button you need to watch the internal flashing light to know what mode its in and when it is taking video or pictures as well as when it is turning off and charging.

The main test is how good the video is. So far we have tested it in good sunlight and late afternoon sunlight. In very good light the video is acceptable but is still not great. In late afternoon light is very jumpy and almost unusable. The afternoon test was walking with the camera and it was very jerky and didnt seem to record every frame. We will need to do a test on the water rocket car under acceleration to see if this jerking video continues.

… update:  …  Well we did stick the camera to the water rocket car to see how good the video quality was while it was moving. The quality is  ok but not as good as we would like.  It seems the camera is just not up to doing good enough quality if the car is moving about. We may be able to use it as a secondary on-car camera or just a stationary camera for the car leaving the cage or something.

Here is some video from the lighter camera (updated with on car video as well)

We will also try the MD-80 camera when it arrives and post a review.

Posted by on January 16th, 2011 1 Comment