Pressure Switch Part 3

March 3rd, 2009

After a rather large break from building rockets I have started to start design and construction for the competition this summer. Whilst I was buying the parts to make more robinson couplings, I saw some other brass components which I thought could be used to make a working pressure switch.

Brass Components Brass Components

The micro switch is clamped onto the two flat brass circles shown above. A balloon is held in between these two brass circles. In theory when the pressure builds up in the rocket, the balloon should expand through the hole in the brass circles and press the micro switch.

The idea is to use the parts to make a pressure switch that can just screw onto a robinson coupling as shown below.

End of Bottle showing coupling Pressure Switch Attached to bottle

Good news first, it works, the micro switch engages at around 15-20psi. Only problem I am having however is the classic problem of making it airtight. After about 40psi there is a notable hiss of air leaking. I will continue to work on it, using some rubber washers and sealent to try and make it air tight.

Pressure Switch – Part 2

December 20th, 2008

I am having a real hard time getting the pressure switch to be fully air tight. The switch works, but after 20-30 seconds, it stops conducting. I am guessing that there is some tiny air leak which is letting in undetecable amounts of air. I have been unsuccessful in sealing the switch any further.

I will continue to explore ways of making a more sealed switch, but I am also looking into other ways of detecting the end of the booster thrust phase.

  • Pressure – Similar to the current switch I am working on, but with a small switch inside a balloon
  • Temperature – According to Boyle’s law as pressure drops, so should the temperature if the volume of the bottle stays the same. A thermistor should be able to detect this.
  • Water Sensor – Detects when all the water has been expelled from the rocket.

Pressure Switch

December 7th, 2008

I have been working on a pressure switch which will be an essential part of our multi stage rocket next year. The idea came from Air Command Rockets.

The pressure switch is made from a old TV remote control button. The membrane and the circuit of a single button are sandwiched in between to small metal plates. This in theory should seal the air inside the rubber button. This is then placed inside the pressure chamber.

As the pressure chamber is pressurised, the air pressure forces the button to be pressed and hopefully presses the contacts on the circuit board. When the rocket launches, the pressure will fall and the button will depress, disconnecting the circuit. A circuit will look for the switch disconnecting and will then trigger the staging mechanism. I am hoping to test this soon and will report findings.

PIC Chip Programmer

December 1st, 2008
Velleman 8048

Velleman 8048

I’ve gone and bought myself a PIC Chip programmer to play about with. Its the Velleman 8048 kit and comes with a 16F627 PIC.

I am intending to hopefully use a PIC Chip to replace the two chips used in the current Optoelectronic Apogee detector circuit.The supplied PIC has both a onboard comparator and Pulse width modulation on some of the outputs, meaning that only a handful of external components will be needed to construct the circuit from now on.

Once I have that working, I can then hopefully change the code to introduce failsafe features to release the parachute after a certain time period, in case the circuit fails to detect the rotation of the rocket. However I have never used PIC chips before both on the electronic and the programming side so it will be an intresting journey. I will report my findings as I go.

12v Compressor

October 15th, 2008

I have purchased a heavy duty compressor from Maplins. Its rated up to 140psi which should be ample for our launches since we rarely go above 100psi. But more importantly it is rated for 15 minutes continuous use at that pressure and even longer at lower pressures.

This is very important for launching water rockets as most compressors seem to burn out trying to pressurise larger rockets, I’m hoping this heavy duty one will be more suitable.

Once the weather starts to warm up next year I will test it out.

Rocket Nozzle How To

July 17th, 2008

I have created a guide on how to create the rocket nozzles we used on our recent rockets:-

Possible reasons for Louie veering off course

July 12th, 2008

Over the last few days I have been watching the videos from the competition over and over to try an get to the bottom of Louie veering off course at the start of the launch. I have also been discussing the problem at the Yahoo Water Rocket mailing list (see:

One thing is for sure, that the rocket is stable in flight, its centre of gravity is well above its centre of pressure. Also the rocket only seems to be unstable at low velocity’s, this confirms that once sufficient velocity has been achieved and drag is being generated by the fins, the rocket is stable.

Various reasons have been suggested for why the rocket is unstable at low speeds, including cross winds, not enough pressure, a bent rocket or a off centred nozzle.

The low launch pressure means that the rocket will have low take off velocity so the fins won’t generate drag for the first several meters of flight, during this period the rocket will be very susceptible to external forces that may try to steer the rocket off course.

Of the remaining causes I suspect the most likely one might be the off centred nozzle. I can’t confirm since the nozzles have since been removed from the rockets and some unfortunately lost.

One very good suggestion was to angle the fins along the vertical plane by 5 degrees, this should put the rocket into a spin thus canceling out any off centred nozzle or bent rocket. The only thing that remains to be seen is if the rocket will be traveling fast enough for the fins to make the rocket spin. I intend to test this next week and report the results.

Some pictures from the competition

July 6th, 2008

Video from the competition

July 6th, 2008

I know its been a long time since the competition but I have been busy with so many things, I haven’t had a chance to update the site. I should now have a couple of weeks free to start working on the rockets again. First task I have set myself is to start uploading some of the pictures and videos from the competition last month.

Below is the video of Louie taking off and then veering to the right and heading into a load of trees.

I was quite disappointed that it didn’t launch straight, I intend to do some slow motion replay to try and work out what happened.

If anybody has any ideas why it did that, please let me know.

The competiton

June 10th, 2008

I am proud to say that the hard work me and my scouts have put in over the last few months paid off, as we took home the trophy for the water rocket competition. Overall the competition was a great success with 6 teams entering and lasting for just under 2 hours. All the scout groups who took part thoroughly enjoyed themselves and we are looking to repeat next year.

Despite winning the competition, I wasn’t happy with the performance from the rockets. Below is a brief summary of the launches.

Louie, the large 4 bottle rocket struggled to accelerate up to speed and when it did, it veered off to the right, into a tree. The second launch was more vertical but didn’t achieve near the height I was hoping for and the parachute failed to deploy, badly damaging the parachute module on impact. I believe the parachute failed to deploy in this instance due to the string holding the door getting tangled, although the impact shock it so much I can’t be sure. Louie was retired after this, as we needed to try and get a good air time record.

On post calculations after the competition, I believe the cause of Louie’s poor performance to be due to low launch pressure. Louie weighs around 600g and was filled with bout 1600-1800ml’s of water. When I put those numbers into a simulator, at 70 psi the rocket would have struggled to have got off the launcher. The first launch was done at 80 psi and second at 90 psi. Its quite clear to see that the first launch had only marginally more pressure than what was needed to lift the rocket a couple of feet.

Doing some more calculations, 120psi would have gone over 300ft and 130psi was starting to near 400ft. Before this I had given up on 4 bottle rockets thinking the size of the nozzle we use are two small. But on reflection if we can get enough pressure in them, I think they should perform very well.

Huey was used for the third air time record, its first flight ended in disaster as the rocket powered up to a record height and then proceeded to fall with no parachute. I think the parachute may have not opened due to the angle of the light sensors. When the last two circuits were made, they had longer wires on the light sensors meaning that they pressed against the inside wall of the bottle, making them point more vertically. With the low position of the sun in the sky at launch I think it may have caused the circuit to be unable to determine the orientation of the rocket. Anyway the parachute module was destroyed on impact.

The last two flights for Huey were for egg recovery’s. For the first flight I had managed to repair the parachute module from Louie and to my delight it worked, safely bringing the egg back to the ground. However as I pressed the reset button on the parachute module for the next launch, a wire came unsoldered, rendering the module useless. I launched again with no parachute but to no surprise the egg was destroyed. As a comical finish the rocket then got chewed up by a dog shortly after crash landing.

Dewey was the only rocket that consitantly performed. As the horizontal rocket it acheived the top 3 distances every time.

I hope to post some further anaylsis over the next few weeks after I have watched some of the video footage. As well as some videos and pictures and some ideas for what can be improved on for next year.