Archive for the ‘Launch Days’ Category


Launch Day – WRA Speed Record Attempt

Launch Day Preparation

After our latest car updates, camera and marker developments we were  finally ready to have a shot at a WRA Dragster record. We decided to try for the speed record first.

For a submission to qualify we need to meet the rules as layed out at

We prepared the car with two onboard cameras, one looking forward and one looking sideways. We also prepared our coloured cups to place on the 10m road markers so that it will be easier see the car pass the road markers.

MD80 Camera mount behind the front wheel

MD80 Rear Mounted Camera

We also decided for this launch day to use twitter to provide live updates from the launch day. We setup and tested a twitter client on our iphone and it worked well. Twitter updates are appearing on

Launch Day

We arrived at the launch site at approx 2:30pm and setup the launcher and the cage, at this point we realized we had forgotten our two normal camera to capture the run, so we decided just to use the iphone video camera and ty to hold it as smooth as possible.

We then measured out the course with our 50m tape measure and marked every 10 metres with a solid chalk line across the road. From the northern end we then marked the 45.7m mark with a dashed line. We then put the red cups every 10m, the blue cups every 50m and the green cup at the 45.7m mark.

We did some twitter updates, then turned on the two car cameras, turned on the electronics for steering, filled the car with water and bubble bath and locked it in on the launch rail inside the cage. Heres how our launch went



We were happy that all of the videos were ok. We used VirtualDub to calculate the time it took for the car to reach the 150ft marker. To do this we used the side looking camera and went through the video file until we found the first frame where the car launched, this woudl be  our starting time. Virtualdub works out what type of file it is and how many frames per second the camera captured. For the MD80’s  each frame was 0.032 seconds.

We then went through the video file frame by frame until we could see the coloured cups in the frame. We then took the used the time from virtualdub for that marker when we saw the white line and the cup one frame past the centre of the frame of the camera. We listed the time to pass each marker then calculated the following

– Relative time to pass each marker putting the first frame as 0 seconds
– Time to move from one marker to the next
– Time to reach the 150ft marker
– Average Velocity at each marker
– Instantaneous Velocity at each marker

This information is available in a spreadsheet for each run   Dragster Speed Record Attempt

The results were

Speed record
First Run 4.94
Second Run 5.32
Average 5.13
First Run 122m
Second Run 100.5m
Average 111.25m


Here are some graphs of the cars velocity as it made its way down the course

Run 1 - Velocity Graph

Run 2 - Velocity Graph

We think we have done enough to get the Dragster Speed Record with these runs. We  will submit the video and spreadsheet to WRA for peer review and hope that we get it accepted :)

Posted by on April 9th, 2011 Comments Off

Tweeting our Next Launch Day

This Sunday the 3rd April at approx 2:30pm Sydney time (GMT+10 or 04:30am 3/4/2011 UTC time) we will have a launch day to try the new updates on the water rocket car. We may even have a shot at the Dragster Speed Record if things go well.

We will try out something new for the hobby and use twitter to provide updates, commentary and photos in real time during the event.

Updates will be via our Twitter Page

If your a regular tweeter then you can go to our twitter page and follow us now then get our updates as we post them.

We will use the hashtag #waterrocketcar for all posts

If you are not a regular twitter user thats ok too, just go to our twitter page above about that time in your local area, or check out our HHWRSA web site (this site) and look in the sidebar to the right —-> under the Twitter heading and updates will be there too.

Here is a good time converter, remember our time is Sydney Australia Time, and no daylight savings tomorrow :)

Posted by on April 2nd, 2011 Comments Off

Launch Cage Test Day

We were fairly keen to try out the new launch cage so even though it was 33 degrees C (50 degrees C on the asphalt) last Sunday, we ventured out to our local launch  site to test the water rocket car with the new launch cage at launch pressures.

The water rocket car had the reinforced triple stack of bottles attached, which have been tested to 180psi. We also had the upgraded launcher using the high pressure hose, both of which hadn’t been run on the car before.

We were also trying out the new MD80 Camera which is a light camera mounted to the water rocket car.

The aim of the test day was to see how the car would launch out of the cage, if it was sticking in the guide rail or not launching straight. Here is the video of the launch day.

Its not shown on the videos, but we did do a 60pis test and an 80 psi test before doing the 120 psi & 125psi tests. The 60psi and 80psi tests worked fine so we increased the pressure up to launch pressures. We didn’t include the video of these launches as they were not really all that  spectacular :)

We were pretty happy with the results of the cage test. The car on both high pressure launches is leaving the cage straight and there doesn’t appear to be any major loss of speed due to friction using the guide rail. There doesn’t appear to be any recoil of the cage and launcher and the cage held together well on launch. Getting the cage to the launch site also worked well, only issue was some strangle looks we got on the way there ;)

The MD80 camera worked ok, but we still have a few teething issues to work through as the first run didn’t record, or most likely, the second video recorded over the first one. We will work on that and possibly download videos from the camera between runs using a laptop, just to be sure.

The car once it left the cage was turning left, this was most likely just a slightly sticking front wheel, the wheel bearings were not greased before this test as we were not going for distance, which would account for the minimal rolling distance as well as the left turn. This should be easily fixed.

Here are a couple of video images showing the water rocket car launching. One of these is now posted on the dragstrer competition page on , the page is here

Launch 2 - 125psi, very clean exit form the launch cage

Launch 1 - 120psi, nice exhaust plume when leaving the cage

Posted by on February 2nd, 2011 Comments Off

Water Rocket Car – Demonstration Day

We were very fortunate this month to be invited along to Killara High School here in NSW to give a demonstration of our Water Rocket Car.

Murray Arnison contacted us through the HHWRSA website explaining he would  be  teaching his engineering class about water rocket cars this term and if we would be interested in coming along to do a demo. We were more than happy to oblige :) We organised for Mark to get the morning off school for this special science excursion.

We spent about an hour with the class showing the Green Hornet Water Rocket Car as well as the launcher and pump and how it all worked.

We used 100psi and 1L of water to ensure the car wasn’t travelling too fast across the quadrangle and several volunteers from the class waited on the other side of the quadrangle to stop the car plowing into surrounding  brick walls. Here is the short video of the launches.

A big thanks to Murray and the students, we had a great morning.  Good luck with your water rocket car designs and testing this term !!

Mark did a powerpoint presentation to his class the following week explaining about  water rocket cars and how we had developed it from a 1 bottle car to what it is now. He  even took the Green Hornet  in to show the class. Everyone including his science teacher was very impressed.

Posted by on August 18th, 2010 Comments Off