Archive for June, 2009

 

Water Rocket Car

Its science project time at school and Mark wanted to build an air powered car. After some initial work with a light cardboard car, a balloon and a straw we decided this just wasn’t going to cut it .. science needs to be more fun than that … we needed to bump it up a few notches .. .ok … you can see where this is going.

The water rocket car project started last weekend. We tried using some existing toy cars with a small bottle of about 600ml, but even at 30psi the rocket cars were not stable. They would basically go of fin any direction and not stay on their wheels … basically unpredictable.

This was a problem, because if Mark was to show this at school it had to be somewhat predictable. There were going to be kids around. So we went about building a car that had a long wheelbase and a low centre of gravity. It was a trade off between how heavy we made it and how safe it would be…

Water Rocket Car

Water Rocket Car

We ended up making the car out of 4 bike training wheels, some 12mm ply board, some metal angle brackets (I had lying around), some cable ties, screws washers etc. We also started with a single 1.25L bottle, but upped that a bit to 1.5L bottle for better performance

The first launches were ok and it was basically working but we were getting pretty wet as the release of the wrocket was manual. We made some alterations to the vertical wrocket launcher to turn it into a horizontal launcher.

Horizontal Wrocket Car Launcher

Horizontal Wrocket Car Launcher

Here is the launcher in the horizontal configuration, basically just removed the feet from teh existing launcher and drilled a hole through the base for the launch string and mounted some extra weight. We needed the extra weights as the lauhcer then wasnt stable and was getting blown backwards .. it was more dangerous than the wrocket car itself.

UP Close of Launcher and release string

UP Close of Launcher and release string

Fornt view of the launcher

Fornt view of the launcher

Its not exactly pretty .. but its functional :)

We then had to try to get the car to go somewhat straight. It is a bit hard to tell as there is practically no level land where we live, so we took it up to the local basketball courts to try it. Since it was raining this weekend we had the place to ourselves.

After two runs at 100psi and some quick wheel alignment with a cordless drill with a phillips bit . we had it tracking straight.

We did a few tests with air only, 100% water, 550ml water at 100psi, 120psi 130psi and 140psi. Most of these are on the video. See below

After the 140psi launch there were stress cracks visible on the neck of the bottle, so we will replace the bottle for the demo

Stress Fractures in Bottle after 140psi test

Stress Fractures in Bottle after 140psi test

I think we ended up with a reliable water rocket car that will be safe for the school science expo demonstrations. We will probably only run it at 100psi for the demo’s and will have a well documented launch and safety process. We went through this safety and launch drill many times today …

One fun part we realized was that if you mess up slightly it doesnt matter, so damaged nosecones :) …. just fill it back up and try again.

Posted by on June 21st, 2009 Comments Off