Water Bottle Rocket

The task

During the second semester, we were assigned a group project to design a water bottle rocket, that would land in a designated landing zone, the scenario was to provide aid to a flooded area. We would be delivering a random payload of between 20g-150g & to random distance between 60-90m that was to only be revealed on launch day.

We also gave three stage gate presentations to show our progress & justify our design choices.

I refined my teamwork, CAD, programming & manufacturing skills throughout this project.

Pressure rig

During workshop sessions I built this pressurising rig following a standard design & manufactured it to tight tolerances needed. A variety of processes were used, from lathing stocks of aluminum & steel, but also milling, 3D printing & centripetal casting. The above picture shows the rig without the locking pin in.

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This picture shows the locking pin fitted which deforms the two arms keeping the bottle in place until the desired pressure is reached.

The angle adjustment rig CAD

Angle adjustment rig

Of course, to launch in the manner needed, we would need some sort of rig to adjust the angle.

I designed the angle adjustment rig from scratch in CAD.

I also created the .dxf files to be laser cut & assembled the launch rig.

Although here I encountered some difficulties with the laser cutter as it did not do all the way through the plywood due to the mirror being slightly dirty.

Assessing for fit during the design phase on CAD first before cutting helped to prevent any mistakes.

Manufacture

Design was laser cut out of 9 & 6mm birch ply. I made small test pieces first to check the tolerances of the slots before committing large amounts of material

Logistics

A key benefit to this design is that it can be flat packed so that it does not take up an unnecessary amount of space while in transport & can easily be assembled when needed. An important consideration given the humanitarian nature of the project. I was inspired by IKEA furniture

Protractor Markings

I added some laser engraved protractor markings to make finding precise launch angles a breeze.

Tolerancing T-slots

I toleranced the T-slots to be 0.2 mm smaller than the bolts in the .dxf file. This was so that with some light taps with a mallet would lead to an interference fit between the two components.

Close up of the nut, bolt & washer

This configuration supplied a uprising amount of force & kept the angle firmly fixed.

The finished rig.

All in all, with some sanding, I was quite happy with how it turned out.

Rocket V1

I tried to be resourceful & got quite a few 2L bottles from asking on an online forum for Sheffield, so that I could repurpose old bottles into rockets. This one here was the first prototype, using corflute & electrical tape for fins. As well as a bottle top for a nose cone topped with a table tennis ball.

MATLAB & Simulations

MATLAB was also used to create plots to show how values of pressure, volume & angle could vary the thrust & distance the rocket would cover.

I modelled the prototype in the open rocket software to check that the centre of pressure (in red) is behind the the centre of mass (in blue).

Testing Protocol

Tasks were delegated to different members of our group to efficiently & safely run the tests, in cadence with a rigorous risk assessment.

We followed the flowchart & ran tasks concurrently when ever possible, e.g. entering launch parameters & filling the rocket so that the tests could take place quickly.

As we would need to ensure that we launched over a 3m obstacle.

This easy to transport, collapsible 3m+ tall marker was made out of recycled wooden pallets by one of our group members to help verify our tests validity.

It was placed at 60m measured precisely with the aid of a golf rangefinder, which was recommended by a golf enthusiast in our group. We also used it to find the distance that the rocket landed.

Full rig

This is roughly what the full rig looked like at the end, with a bike pump attached, as well as the locking pin secured.

Testing

The image to the left shows the 3 meter marker made out of old pallets by a member of our group, I also attached my action camera to the top to record the launch.

The video below shows a test launch with 150g & the rocket clearing the marker handily.

IMG_9108.MOV

Test results & MATLAB comparisons

We split testing over two days, the first day reveled that my design for the rocket had some flaws, there wasn't enough padding & it had cracked the payload container & table tennis ball. So for day 2 a padded vacuum molded nose cone was constructed & attached more securely. Which held up much better, this design can be seen under the final launch day section.

Given real world conditions the MATLAB's wasn't too far off, the systematic error could be adjusted for.

Final launch day

When the day came, the distance was 75 m. To make sure the masses were consistent with our testing, we added some bolts inside the nose cone (of a known mass) to make a consistent 150g.

Out of our 3 rockets, 2 landed in the zone & 1 just over shot, this scored joint second in the cohort out of 50 groups.

To summarise, I worked in a group to design, test, manufacture & launch a water bottle rocket with a humanitarian goal.

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