6.75L Water Rocket Car + Crash .. Big one !!

[thampson]

This weekend we finished building and got to test our 3 bottle water rocket car.
This is the design we have been working on for a couple of weeks. It uses 3 x
2.25L bottles with robinson couplings. We had a bit of messing around with
leaks, but eventually hydrostatic tested at 140psi with no leaks.

We also greased all the bearings in the wheels and they had less rolling resistance.

We got to put 2 test runs on the car. First impressions were that this car is a
lot faster than the previous one, it also takes a lot longer to bring it up to
pressure .... no need to go to the gym ... I got a good workout just pumping up
the wrocket twice

We have got some work to do on the steering. We did do some unpowered pushes to
get it tracking straight prior to the two launches but the car went both ways
under power. It doesnt look like an aero issue, it was just a gradual turn in
the big crash and a turn while in cruise on the first run.

Have a look at the video to see the results ... the rebuild is pretty straight
forward .. but i do need to come up with a better solution for steering ....

[youtube][/youtube]

I will do a writeup on our website to show some of the construction pics ...

Im pretty confident 100m is easily within reach of this car .... maybe we will
aim for that next week

-todd-

[Spaceman Spiff]

This weekend we finished building and got to test our 3 bottle water rocket car.
This is the design we have been working on for a couple of weeks. It uses 3 x
2.25L bottles with robinson couplings. We had a bit of messing around with
leaks, but eventually hydrostatic tested at 140psi with no leaks.

We also greased all the bearings in the wheels and they had less rolling resistance.

We got to put 2 test runs on the car. First impressions were that this car is a
lot faster than the previous one, it also takes a lot longer to bring it up to
pressure .... no need to go to the gym ... I got a good workout just pumping up
the wrocket twice

We have got some work to do on the steering. We did do some unpowered pushes to
get it tracking straight prior to the two launches but the car went both ways
under power. It doesnt look like an aero issue, it was just a gradual turn in
the big crash and a turn while in cruise on the first run.

Have a look at the video to see the results ... the rebuild is pretty straight
forward .. but i do need to come up with a better solution for steering ....

[youtube][/youtube]

I will do a writeup on our website to show some of the construction pics ...

Im pretty confident 100m is easily within reach of this car .... maybe we will
aim for that next week

-todd-

Hi Todd. So sorry to see your car crashed and broke. Hopefully the damage can be repaired easily.

I did notice that your son seemed pretty enthused that the car crashed, so I guess that it was a success in the sense that it kept him entertained and interested. I bet you're teaching him a lot!

[thampson]

Yes its safe to say we both enjoy working on our water rockets. Its also good science and engineering for him to learn ....

-todd-

[Spaceman Spiff]

Yes its safe to say we both enjoy working on our water rockets. Its also good science and engineering for him to learn ....

-todd-

I think you should try to find lightweight parts for your car. I noticed from your video you have wheels that look pretty hefty. I remember from scouts many years ago we had this contest called "Pinewood Derby" and every scout would build this little car that we would race down a ramp and the fastest car would win. There are all kinds of tips for modifying the stock parts to make the cars go faster. Some of the methods were ruled out as cheating but they could be helpful in your cars. The one I remember was making the wheels lighter because the mass of the wheels has inertia that you need to overcome as the car accelerates, so lighter wheels will make the car accelerate faster because of their weight and the spinning inertia.

[RaZias]

It would be cool to make servo controlled wheels, so in a long distance you could remotly control the car.
Just take a system of a radio controlled car and adapt it, you will also need to increase the signal range.

[Spaceman Spiff]

It would be cool to make servo controlled wheels, so in a long distance you could remotly control the car.
Just take a system of a radio controlled car and adapt it, you will also need to increase the signal range.

What about if you used one of those line following algorithms and some optical sensors and servos to keep the car from going off course by having it follow a painted line on the road? Then you don't need any radio control.

[thampson]

following the painted line sounds like a good idea .. but I dont think the council would like me painting lines all over their road ..... the rc control will be worth a try first I think

-todd-

[Tim Chen]

following the painted line sounds like a good idea .. but I dont think the council would like me painting lines all over their road ..... the rc control will be worth a try first I think

-todd-

What if you used a roll of tape or a ribbon as the line to follow? Then you could just roll it up when you were done and they couldn't complain!

[U.S. Water Rockets1]

Todd,

Have you considered making a frame for your rocket car out of PVC Pipe? It would probably be a lot lighter that way, and you could build it in a modular form that could be pieced together and reconfigured for different bottles and engine configurations. You could only glue the subsections together and use friction fit to join the sections like a giant "LEGO" set.

We made a portable external launch tower that would "snap" together from PVC "trusses" a while back. It was really impressive looking but the launch rail never worked really well for us. The truss idea would be cool for making segmented dragsters.

Plus, the PVC won't soak up water and make the car heavy.

[thampson]

Thanks for the suggestions Tim and US Water Rockets ...

I like the idea of a light snap together body .....but I fear it woudlnt last 1 launch if it hit the gutter at the speeds we are currently doing .. it may not look it on the videos but its hitting with a huge amount of force ... the crashes are breaking pieces out of the plywood chassis and ripping screws clean out ....

If we can manage to sort out the stability and steering then its definately worth a shot with a lightweight body to go for a distance record .. Im going to have to find a new launch site .. .... wheres that airstrip ... LOL

cya
-todd-