Water Rocket Car MkVIII - Launch Day - 96m (315ft) distance

[thampson]

We had a launch day on the weekend to try out the new rear wing and 6mm nozzle. Good news is we did bring the car home in one piece and we did increase our distance record out to 96m (315ft). So all in all pretty good.

The launches were not over dramatic but thats ok ... We did have an issue with the launcher which we need to fix and the 6mm nozzle was probably a little undersized as there was still some water in the bottle after the launch.

The video is here



The write up is on our website

http://wrocket.hampson.net.au/?p=971


Some more development is in the works

We are trying out different sized nozzle inserts on the test stand and will report results on these soon. We are trying out some interesting configurations like multiple small holes to see if this will induce more expansion of the water air / mix after leaving the nozzle ...

We have a radar gun ordered which should be delivered this week .. This will give us some real measurements on the speed of the car. Its a Hot Wheels unit, but it is a real 10.525Ghz radar gun which will clock up to 160km/hr (so it says). This is not my video, but shows the radar gun in action.



Cant go too far wrong for $20 off ebay

Also we have on the way a Futaba 2PH 2 Channel R/C Transmitter, receiver and servos, again from ebay.

http://www.gpdealera.com/cgi-bin/wgainf100p.pgm?I=FUTJ12**

We will be attempting to rebuild the front steering and fit the R/C receiver and servo to the car. We looked at using an existing R/C car for parts but most of the cheaper ones have plastic components, and the ones that look to be up to the job are very expensive, so we will give it a go first

-todd-

[RaZias]

I am preparing a launcher for a WR-car and I am having in mind to set a speed record instead of a distance record.

The problem for a distance record is to have space for it, if someone wants a 300 meters record I think it will have a problem. That´s why I am working in a speed record.

The launcher is made for high-pressures and I will use a small bottle, so it will have more thrusth and less impulse.
I would like to see someday a 140km/h WRC in a short distance!

The problem to use a bicycle velocity device is that is configurated for the size of the wheels bike and not for the one of the WR-car.
So the radar gun is a good thing.

[WRA2]

This looks like a good place to bring up discussing competitions for water rocket cars. What would everyone want in a water rocket car competition. Distance, maximum speed, accuracy (driving it through some kind of course, delivering a payload safely (egg maybe) or driving it to a target (closest). Most of the flight rules which we already use could be applied (safety rules, launcher rules, etc.) The question arises though on how to record the record as having fellow competitors or administrators at every record attempt would be impractical and silly since competitors here are from all over the world. For our flight records we use electronic measurements such as the video from the onboard camera and the altimeter data. Videotaped evidence showing the scale of the course/track might be a good starting point. Another thing is that the measurement devices would have to be comparable cost wise to the cost of the devices required in the other competitions (no military radar systems, police radar, etc.). Another issue may be how do we tell if the competitor launched their water rocket car downhill.

Here is a summary of the key points to discuss.

1. Electronically verifiable. (measure speed course length and distance traveled)

2. Type of competition (distance, speed, accuracy, payload delivery)

3. Water rocket car specific rules (weight limit, track layout, construction materials)

[RaZias]

There are devices for bycicles that measure the inclination of the road.

[thampson]

Here are my thoughts for discussion.

1. Types of Records - I think distance and speed records are the two things that would be of interest and could continue to be increased. The driving a course once its done is done really. Maybe also a class system like you have for the rockets ie: Single bottle 1.5L and an open class ie: unlimited capacity. There would probably need to be some rules for not allowing super heated steam powered rocket cars as this is a different class altogether.

2. Electronically verifiable - I have tried a bike computer to get speed reading and distance but they are unreliable on both counts. The speed reading has a maximum limit of the reed switch as it will only record so many rpm's, anything beyond that it just cant handle, for bikes with 22" wheels its fine because it would mean the bike is traveling at 100km/hr doing that many rpm's, but for our rocket car with smaller wheels it max's out at 21km/hr at this same rpm. It also doesn't record the distance traveled for the times when its actually traveling over 21km/hr, which gives incorrect distance readings.

We are going to try the low cost radar guns to see if these give a reliable speed reading. We will report back on the success of these.

For distance we currently just step it out. I use this method a lot for work (for wireless surveys to dimension buildings ) and know my step is 1.05m but this is not really verifiable. I looked at the option of using a GPS reading from my Nokia N95 at both ends of the run, then using Google earth to calculate the distance. The gps co-ordinates themselves (even with 13 decimal places of accuracy) we not accurate enough as when I put these on Google earth they didnt correspond exactly to where i was when I took the readings. The measured distance was at least 10m out. I may try some further tests with this method to see if my initial tests had induced human errors .. ie: me Although maybe not everyone has access to an accurate GPS device.

I checked a launch distance using the ruler feature on Google earth and its pretty accurate, within 2m, so this method may be able to be used with video evidence and a Google earth kml file of the location to verify a claim. I have looked at lower priced laser distance devices but most of the cheaper ones max out at 30 or 50m which is not good enough for distance records. I think the simplest way will be to use a tape measure and record the measurement on videotape. You can buy a 100m tape measure for A$45 (or 50m for A$39) on eBay. As long as the entire measuring process was on tape this should be sufficient for accurate measurement, the Google earth file and video evidence could be used as an additional method to check the claimed distance.

3. Ground Slope - I know from experience of looking for flat areas to launch the car, that its virtually impossible to get a long stretch of perfectly flat surface without some slope. Usually there is some slope for drainage, the flattest areas we have found are basketball courts, but we have outgrown them now and need to use roads / carparks. A couple of options available here are possibly

a) require a run in both directions and take the average distance
b) Only allow up to a certain percentage of gradient on the road. I know my N95 has an app that uses the accelerometer to measure the gradient of the road, but this technology may not be available to everybody.

I think option a) is probably the fairest as it cancels out the issue of surface gradient

Interested to see what other people think as well. Ive attached a pic of a 100m tape measure ... measures in feet too

thanks
-todd-

[WRA2]

Thanks for the well thought out reply Todd,

The two runs in opposite directions is a great idea. That would be the same as all other land speed records and is similar to our two flight rule we have for the altitude competitions. We should develop the distance competition rules first since it will offer the least expensive ways of measuring.

Maybe the competitor could measure out and mark the "track" in 100 meter divisions and videotape the measurement from the car "post run" to the last measured mark as part of the submission. The competitor would then turn the car around and run the opposite way from the closest 100 meter mark and repeat the process. distance would then be averaged for the two runs.

We will need to all decide how to limit the size of the "car" to something reasonable otherwise it will turn into a "who has the biggest budget" and can afford to build the largest car competition. With altitude competitions there is a 1500 gram weight limit for rockets to be considered "hobby" which need no special air traffic clearance or "high power" license to fly. We choose this limit so that everyone could compete anywhere and not be restricted to pyro meets. We should come up with something similar for the cars.

Another thing we may need to look at is the use of commercial parts like old RC cars etc. The competitor should make the car from discreet components.

Anyone else have some suggestions?

[Tim Chen]

I like the idea of doing 2 runs in opposite directions on the same course to cancel out gradients or wind direction. Maybe you could use google earth to insure that the area is relatively flat as well. If you did a run on a course with a steep hill in the center, the car may actually go farther because it would be rolling downhill during the coast phase on each run. I think the topographical maps in google earth are probably accurate enough to tell how flat the area is.

So, a fairly flat surface and 2 runs averaged would make for a pretty fair contest.

It would be cool if one of those "hot wheels" radar guns could be made to work with this speed contest. I wonder how accurate they really are.

[RaZias]

I do montain bike and there is a category named free-style. It´s about jumps and acrobacys.

I was wondering if a jump contest would be fun, like in those shows where motor-bikers jump over a set of cars.