Initial Prototypes 

We made out initial prototypes during the first couple of week of the project and they were mostly for us to gain a better understanding of what the rockets will look like and how different aspects will work. These prototypes were very simplistic and were comprised of two bottles, one cut and stuck on top of the other (acting as a basic nosecone), and cardboard fins. We made two prototypes, one with three fins and one with four fins and used them to observe their flight and determine by observation which flight looked more balanced and stable. Before testing, we put electrical tape and stones in the gap made between the main rocket body and the nosecone end  to add weight, bringing the centre of mass towards the front of the rocket and creating a more stable and balanced flight.

 

 

 

 

 

 

 

 

 

 

 

 

Final Prototype

Our final prototype was significantly more put together than the previous ones as we made them at a much later date with designing all complete. There were flaws and mistakes made, but the point of prototypes is to make improvements so the final rocket doesn’t process these problems. We 3D printed three nosecones, however we assume they were taken because we could not find them when it came to collect them. This was a bit of a setback, however we went about making a foam nosecone by hand.

The Nosecone

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As shown in the photos above, we took a block of solid foam and cut it until it was a near enough shape that we could grate it down into a smooth curve, then sand it to have an even smoother surface. In retrospect, we should have found some less dense foam as this was tough to work with and heavier than we expected. It took especially long to hollow it out:

We first had to use a crafts knife to give a circular boarder to work around. Initially we used a tool to chip away at the inside, but this was taking too long so instead we used a drill. Conveniently, the drill was a similar size to the bottle cap, so we made a hole to fit it in the centre so we could glue in the bottle cap and essentially have a screw-on nosecone. After, we smoothed it over with a filing tool to get rid of ragged edges.

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After we made this foam nosecone, we found someone who would 3D print our CAD nosecone so we managed to receive two hollow, 3D printed nosecones for our final rocket.

 

The Fins

We made our fins out of fairly thick cardboard. We chose a sturdy type of cardboard that wouldn’t easily bend as we put it on or transported it. We chose cardboard over other materials, laser cut plastic for example, because of how easy it is to get hold of and how cheap it is. Everybody has access to cardboard and using it also promotes recycling and reusing packaging

These fins, due to being cardboard, got wet during launch and were made useless by this. For this reason, for our final rocket we layered the cardboard fins with electrical tap as a waterproofing layer.

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When attaching the fins, we had to ensure they were evenly spaced. This was hard, however, due to the fact that the bottle is circular. In order to manage to put them on evenly, we took a piece of tape and wrapped it around the bottle, removed it, and then measured it. We could then divide the length of the tape by four and put markings separated by a distance of the value just found. We could then wrap the tape back around the bottle and simply attach the fins in line with the markings so they were approximately 90° around the bottle from each other.

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Attaching and Making the Parachute

In keeping with our materials being easily sourced and cheap, our parachute is made from a plastic bin bag. This bag is cut and attached with string to the main body of our rocket and is then tucked up in the nosecone. When the rocket descends, the nosecone falls off and the parachute is released. For our prototype, this didn’t quite work due to a few issues.

The first problem was with how we attached the parachute’s strings to the main body. When doing this with our prototype, we made holes in the main bottle to insert the string. Of course, we soon realised this was an issue for keeping in the pressure and we found during launch attempts that the air would escape even with the holes taped up so we couldn’t get the maximum pressure we wanted to launch the rocket as high as possible.

The second problem was with the release mechanism itself. The string we used to attach the parachute ended up being too thick and so the nosecone wouldn’t go on easily and would subsequently get stuck and not fall off during descent as it was supposed to.

These mistakes made during the prototyping process meant we didn’t make them during the main assembly. We used wool, as it was all we could find available, which was much thinner and much more suitable, and then we taped it on rather than making holes in the rocket. During our test launches, we also tried a different method of parachute release and, rather than having it hidden in the nosecone where it may not get deployed, we had it on top of the nosecone during launch so there was no way it would get stuck inside.

Our final Prototype:

Below are three of our prototypes. One has the foam nosecone which we made and the other two have 3D printed nosecones.

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We reused certain parts of the prototypes for our actual rocket, for example the pink nosecone is the same that is attached to our final design.
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Our Final Rocket:

Below is shown our final rocket for the launch day. The fins are waterproofed by tape, as seen, and the nosecone is attached, with a weight at the top for stability, so that it will come off to release the parachute which is tucked inside. The micro:bit is attached to the rocket inside the nosecone too and is attached in a way that it will be accessible on the day. 

 

 

A look into our prototyping and fabrication process in greater detail can be seen below, with details on tools and dimensions we used: