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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Water Rocket Car MkXI - Onboard Camera + 474ft team record

Discussions about water rocket powered cars, sleds or boats.
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thampson
Current WRA2 Dragster Speed & Distance Record Holder
Current WRA2 Dragster Speed & Distance Record Holder
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Water Rocket Car MkXI - Onboard Camera + 474ft team record

Post by thampson » Mon Aug 02, 2010 8:23 am

In quite blustery conditions we had a launch day on the weekend. Lucky for us we can launch in conditions that leave most rocketeers grounded :) Since the last test we have discarded the low friction rear wheels and returned to the standard wheels. We have fitted a camera, an old 3 Mpixel one we had lying around, it didnt matter if it crashed and was wrecked. We also tried out the mist attachment for the first time in the horizontal position.

The video explains most of it, so here it is :)

http://www.youtube.com/watch?v=cWn9FzZQubc

We were quite happy with the distances we achieved and beat our previous record of 110m (330ft) by a long way. The 120psi launch could still have gone further except we ran out of road. There was a bit of wind but Im very confident we could achieve that distance on a still day as well. The road is very flat and mostly smooth except for a few rocks which we hit towards the end of the run.

If you watch the video during the main part of the run its interesting to see that the smallest steering input causes a big move in the cars direction. I think we are getting better at steering it, too many quick corrections tends to make it fishtail. Its better to make a steering input, let it settle, then make another one, let it settle etc, which is what we did on these launches. Also towards the end of the second run you can see two bigger steering corrections, this was to try not to hit the gutter straight on. That was at about 130m away, the r/c worked flawlessly even at that distance.

The mist attachment didnt work as well as we had hoped. It did provide a good mist plume but too much water was left in the bottles (about 500ml left out of 1.5L). We will make a type of pickup for the middle bottle to try to solve this problem. The foam + mist attachment was a little better but still too much was left in the bottles at the end of the run.

The camera even though its heavy, worked well. We will probably replace this with a lighter model in the near future.

All in all a good day, we managed to bring the car home in one piece, we found a new launch site and mark enjoyed chasing the water rocket car in his wheelie shoes to turn the onboard camera off.

There is a little more detail on our website for those interested

cya
-todd-


HHWRSA
Hornsby Heights Water Rocket Space Agency
http://wrocket.hampson.net.au

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RaZias
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Re: Water Rocket Car MkXI - Onboard Camera + 474ft team reco

Post by RaZias » Tue Aug 03, 2010 6:33 am

Nice improvement on the car.
It´s time to increase the speed, by adding more nozzles or increasing the bottles pressure.
I hope you came with a solution for the water remaining.


Do you consider that adding a extra-wheel at the side of each wheel would increase the stability at higher speeds?
(like the that huge trucks with several wheels...altough they use them for weight distribution.)


Research and Development is the soul of WR

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thampson
Current WRA2 Dragster Speed & Distance Record Holder
Current WRA2 Dragster Speed & Distance Record Holder
Posts: 230
Joined: Wed Jul 16, 2008 8:19 am

Re: Water Rocket Car MkXI - Onboard Camera + 474ft team reco

Post by thampson » Wed Aug 04, 2010 11:43 am

Thanks for the suggestion Razius.

I think there is more to be gained from aerodynamic downforce on the back wheels rather than more mechanical grip from an extra set of wheels (more weight).

We have a triple bottle stack of reinforced bottles which we will probably use next to increase the thrust. We have the new high pressure hose working so we can start to increase the pressures now.

I will post an update when we try it out.

cya
-todd-


HHWRSA
Hornsby Heights Water Rocket Space Agency
http://wrocket.hampson.net.au

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U.S. Water Rockets1
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Re: Water Rocket Car MkXI - Onboard Camera + 474ft team reco

Post by U.S. Water Rockets1 » Sat Aug 07, 2010 10:29 pm

Congratulations on the new record, Todd.

Have you considered adding a lever/fulcrum to the steering mechanism so that a very large range of movement of the servo is reduced to a much smaller steering input? You usually have the option to adjust this with a setting on your controller but that just reduces the movement of the servo motor, which is not the optimal way to dampen the steering inputs.


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