The water rocket is required to perform to a certain level. It is required to fly vertically up at a minimum of 10 meters and reach no more than 8G
2
Environment
All materials used are mostly recycled such as the cork, bottle, wooden forks, or are made from spare household items.
3
Life Expectancy
The life expectancy depends on level of damage on impacts however, the rocket can usually be fixed with simple equipment but in the testing done a suggested 10-20 uses would be suggested.
4
Maintenance
No maintenance is necessary on this product however, if maintenance is needed it will not be difficult. If the rocket becomes dented or damaged, it should be easily repaired.
5
Target product cost
The cost of this product will be cheap. Most materials used are recycled or household items so cost will be to a minimum, a guide is provided and can be altered to fit the client’s needs.
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Availability of components
All components are easy to get hold of, we recommend using second-hand bottles and corks. This makes it easy to get and cheap to make.
7
Transportation
No transportation is needed, as the products manual can be found online.
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Quantity
The quantity is up to the client as there are simple instructions to create and recreate the product.
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Size
The size of the rocket will be approximately: Height – 500mm x 80mm
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Weight
Without water 160g, with water 660g.
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Aesthetics and finish
The aesthetics and finish are up to the client. Each customer can customize their rocket as they please.
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Materials
The materials advised to be used within the instructions are: Plastic bottles, wooden forks, tape and a cork. The bike valve can be purchased or recycled by cutting the valve out of an old innertube. All the materials we advised to be used are recyclable, and easy and cheap to get hold off.
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Testing
Extensive testing was done and is proven to be safe and reliable.
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Safety
We have carried out testing and found this is safe to use. Additionally, we will put safety warnings on all our products, ensuring everyone uses the product correctly and safely, there has also been a risk assessment carried out.
15
Shelf life
This has an unlimited shell life due to the step-by-step guide being available.
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Disposal
We advise the client to dispose of the water rocket by recycling. This is to be more eco-friendly and to encourage recycling.
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Customer
The customer we are aiming our product at are teachers of secondary schools that will create and demonstrate its engineering relevance.
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Quality
The instructions will be on the website giving a step-by-step guide on how it was made, but this can be used as a guideline instead and create a personalised rocket.
After following the tutorial on how to build you own water rocket, you’re now going to want to go ahead and test it. To do this you will need to attach a cork or bung onto an air pump needed to apply pressure to the rocket.
Next you will need to fill up the bottle roughly 1/3 of the way with water. We have tested the rocket with about 1/6 of water and the rocket was only able to reach about 1 meter high due to there not being enough propellant force to drive the rocket upwards. However, fill the bottle too much (2/3) and the bottle won’t expel all of the water as it will be too heavy, and you won’t be able to apply enough pressure.
The water in the rocket is what propels the rocket upwards due to Newtons third law of motion, that every action has an equal but opposite reaction. Therefore, as the water is pushed downwards the rocket is pushed upwards. However, you are not compressing the water, but the air inside it. The compressed air is what produces the force and the water acts as the mass, combining these two gives the acceleration of the rocket.
Now with this information you can figure out that not enough air means not enough force to drive the mass of water out. And too much air means wasted force as it will run out of mass to push out. That is why the golden ratio is about 1/3 water and 2/3 air.
Centre of mass and centre of pressure.
Now the relationship between the centre of mass and centre of pressure is that the further apart they are the more stable to rocket will be. On a bottle rocket the centre of pressure is roughly where the water will exit out of the rocket. Therefore, you need to apply different weights in the nose of the cone to increases the distance between the centre of mass and centre of pressure. However, there is that golden ratio again, between the rocket being too heavy so its max altitude will decrease, or it will be more unstable. Therefore, a double bottle rocket is more stable due to the large distance between the centre of pressure and centre of mass.
Nozzle diameters.
You can also play about with different diameter nozzles for the water to exit through. Due to Bernoulli’s Principle.
Due to the initial velocity and initial area inside the bottle being constant.
So as you decrease the area of the nozzle opening the water will exit at a higher velocity increasing thrust.
Due to the bove equation there is multiple ways to increase thrust, which are:
– Increase mass flow rate.
– Increase exit Velocity.
– Increase exit pressure.
– Decrease nozzle area if Pe>Pa and increase if Pe<Pa.
Aim.
I aim to test and calculate the acceleration of the water rocket as its released and to calculate the G force experienced during flight.
Methods.
A Microbit will be used to send and receive data that can then be stored and processed to give relevant data in the form of charts. There are two sets of JavaScript, one is “Z-RECIEVER” and the other is “Z-SENDER” The step-by-step guide on how to program the Microbits will be on the website.
Theory.
I started by using a water rocket simulator by Sciencebits.com to get a predicted flight as I can compare it to later tests and see if this initial simulator is accurate, the chart below shows its simulation that would peak at 17m/s and travel a max height of 12.5m.
this is the chart the simulator generated that calculates the flight height and distancethis is the calculations that the simulator ran
These are the calculations and methods used by the simulator to create the chart.
The next charts show the acceleration of the water rocket during actual testing, it was tested on a day that had minimal wind and was pressurized to 40PSI, the charts below shows the acceleration in G hits up to 8G at 40PSI holding 500ml of water, to test the calculations of the simulator I then added more weight by adding more water and lowered the pressure to 20PSI.
First chart shows acceleration of rocket at 8G with a pressure of 40PSI and 500ml of watersecond chart shows the acceleration of the rocket
The added weight and less pressure shows the effect on acceleration by it not reaching the same level of G compared to the first test, this is because added weight and less pressure results
This chart is when the water rocket is at its east efficient with 20PSI and a increased amount of waterthis is the calculation that proves why the rocket is less effective with more weight and less pressure.
2 Microbits are used to send and receive data from the water rocket to measure acceleration in G force, 1 microbit acts as a sender that will be attached to the water rocket and send data to the 2nd microbit that will receive and measure the data.
The Microbit website has a user friendly interface that is simple to use for all ages so is easy to follow and create code as it can be a simple click and drag process or gives you the option to write JavaScript that does the same process.
Sender
The first step is to go to (https://makecode.microbit.org/#editor) and create a new file, the first microbit needs to be plugged into a PC and labelled “Z-SENDER” the code below should then be recreated exactly, once the code is loaded onto the microbit it can be attached to the rocket but its vital the battery pack that came with the microbit is attached and charged otherwise the sender cannot send code, make sure the radio set group number matches between the sender and receiver or it won’t connect.
Receiver
The second Microbit acts as a receiver that will be plugged into a PC while the other microbit is on the rocket, a new file should be created for the Microbit on the website and called “Z-RECIEVER” after entering the code the microbit should be measuring the acceleration in G and will measure it up to 8G, the receiver uses radio signals to receive the data and can be viewed live by clicking the “show console device” this will show the stream of data that can then be copied or downloaded and put into Excel to plot graphs showing the data’s findings.
“Z-RECIEVER” JavaScript“Z-RECIEVER” Simple code“Z-SENDER” JavaScript codeThis is the “Z-SENDER”
Original predicted Gantt chart at the start of the assignmentThis is the actual outcome of the Gantt Chart at the end of the process
The Main difference between the 2 Gantt charts are the alterations to the time scale, the reason these changed are the development and testing took longer than anticipated as originally I had no microbit for testing. Development took longer than planned as it was a continuous process of trying new ideas and seeing if they are a benefit.
as there are many bottles with different shapes and dimensions, I had to select the best bottle shape for a rocket design, this needs to be streamlined and aerodynamically efficient, The second aspect of picking the correct bottle is the capacity of water it can carry because this will affect size an stability as if it‘s too short or too long it will alter the balance and weight distribution. I wanted a bottle that is cylindrical and not square as its easier for air to flow past it.
I chose a 1.5L bottle as I thought this would be a good compromise between length and weight, the length of the bottle on its own is 30cm and weighs 40g, it is cylindrical in chape for the best aero start point.
Step 2: Nose cone
For a nose cone I had a choice between 3 different types of cones, I require some space between the bottle and the cone as I need space for the microbit and a weight for stability.
Type 1: (Green cone)
The green cone would be the most aerodynamic as it’s a cone shape and is shaped around the base of the bottle so no excess would overlap the bottle and effect the aerodynamic efficiency, it is the lightest of the 3 cones at 5 grams as its made from card, because its made from card it will be the weakest and will get damaged after several launches.
Type 2: (Blue cone)
The blue cone would be the second most aerodynamically efficient as it fits the bottle well and has smooth body for air to flow but hasn’t got a tapered nose so it can cause air to hit the cone instead of flowing over it smoothly, as its originally a cup it has 400ml of space for the microbit and nose weight to be stored, its made from a transparent blue plastic and is strong enough to take impacts from launches, but with this strength the blue cone is the heaviest of the 3 at 40 grams.
Type 3: (Orange cone)
The orange cone is the least efficient aerodynamically as it fits the bottle the worse out of the 3 and has a hole in the top so air would be trapped as it is travelling through the air, it is the second heaviest at 20 grams and can hold 200ml so it can’t fit the microbit and the weight.
Step 3: Propulsion
I researched simple water rocket designs and most used PVC pipes and a bike pump for the base and propulsion, but as I didn’t have any adequate piping, I searched for other ideas that can be simple to make using basic equipment.
In the end I had some spare bike valves that would be suitable to use as it can easily be used with any normal bike pump. I first tired using the original cap from the bottle and cut a hole for the valve to go through but ended up using a cork to plug the lid as the original lid couldn’t hold consistent pressure, I attempted to seal the lid with some rubber gloves but still didn’t seal properly, I trimmed down the excess cork with a blade so the bike pump can fully attach to the valve without it being too small and leaking air.
Step 4: Release mechanism
As it states in the assignment brief “There needs to be a mechanism to hold the rocket in place while it is being pressurised and for a period of time after” this mechanism that I used is a pin mechanism that goes through the cork and the bottle to hold in place, I started by drilling a hole off centre of the cork so the valve and the hole drilled for the release mechanism don’t merge as that would cause problems such as the pin catching and not releasing smoothly, I tried some different pins to test which is the better option and found a Allen key fitted the best as it was the right diameter and length, another benefit of the Allen key was its 90 degree bend that I could attach some string to make pulling the pin out safer and easier as I can distance myself when the rocket launches.
The pin material was integral as weaker materials such as a wooden skewer flexed too much and caused air to escape gradually as the pressure exceeded 25Psi in the bottle, I decided stronger materials such as metal would be more suitable as it won’t flex as much as wood and tested different objects such as nails and screwdrivers but found the Allen key suited the criteria best.
I decided the pin would need a length of string attached to it so it can be pulled out from a distance as originally, I needed to pull it out by hand and I found this unsafe.
Step 5: Base
The base consists of 3 different components: the extension on the rocket, rocket legs and base.
The extension on the rocket was used so I could attach legs to the rocket, without this the legs were too short and couldn’t fit the bike pump attachment without falling over, the extension provided a good structure to attach the legs, before the extension the legs needed to be over extended causing them to flex and fail at time as there wasn’t sufficient connection between the bottle and the legs. The extension was made from a thin cardboard and connected to the bottle with duct tape, cardboard was used as it is light and flexible so I could shape it to the bottle, the downside with cardboard on a water rocket is that cardboard doesn’t want to get wet as it can start to damage and deform it as it goes soggy.
The rocket legs are used to create a gap between the floor and the cork so the bike pump can attach fully without hinderance, different types of legs and configurations were tested and found the wooden fork legs was the best choice as they arch out slightly for better stability while not interfering with its aerodynamics, wooden forks were used as they are light (3 grams each) and can withstand getting wet. A triangle was made to support the forks and maximize stability, but the design didn’t work as when the rocket took off after being pressurised the cork would strike the triangle and cause it to come away. I tried using spoons instead of forks and cut slits in the spoons for it to hold each end of the triangle but failed as the wooden material was too fragile and would split.
A base had to be used because there still wasn’t enough room between the floor and the rocket when the bike pump is attached and fully extended, a hole was drilled in the base so the pump can fit without hinderance
Hole drilled for Release mechanism
Original bottle cap with valves
first design
first design (rear)
bottle extension
Release mechanism
Rocket legs with stability triangle
rocket legs
Base with bike attachment
cork design and valve
microbit location
These are the three different types of nose cones that was tested
Water Bottle: I used a 1.5L water bottle costing £1.75, I chose the bottom as it was a smooth cylinder shape with no obscurities so its aerodynamically streamlined.
Nose cone: I used the cup part of a plastic wine glass as the nose cone and cut off the base as I found it fitted the bottle well and was itself a smooth design, which is important to the stability of the rocket and is aerodynamically efficient, it can also hold weights in the nose which helps with balance and stability while in the air, the plastic wine glass set cost £2.00 with 4 in the pack.
Bungs: I was able to find some wine corks that I was able to adapt to work as a bung for the rocket, I driller holes and trimmed down the cork so it will fit in the bottle top without it catching, as I already had the cork, I didn’t need to buy them but I would estimate that it would cost £0.75p each.
Valve: The valve I used was originally used for tubeless tyres on mountain and road bikes, I thought this would be a logical thing to use as I had spares and is designed to work with most pumps, I figured it will be perfect for holding pressure in the bottle without leaking as its designed to keep pressure in with rubber seals. The valves themselves are quite expensive at £5-£6 each.
Platform: I used wooden plates for the base as it is sturdy and also economically friendly as it is made from recyclable materials, I cut a circular hole in the middle of the plate so the pump can fit without causing disruptions to the rocket itself as it made it unbalanced at the base. The paper plates came in a pack of 100 with packs of wooden cutlery as well costing £30, these were purchased and used for another matter but a single plate would cost £0.10p
Rocket Legs: The rocket legs was made from Wooden forks from the same package as the platform, I altered the forks design to create 2 prongs for stability, I used 3 forks as legs and picked the forks as they are light, thin, economically friendly and strong, wooden forks from places like fish and chip shops can be used as legs as an alternative, for costing, the forks came in the same package as the platform for the rocket, and would cost £0.15p-£0.20p each.
Tape: For tape I used Duct tape as it is light, cheap and is very useful to hold the rocket parts together, it holds the nose cone to the rocket and cardboard extension to the bottle. The cost of the tape would be £3.75 per 50m roll.
Release mechanism: The release mechanism I used was a Allen key that was used to hold the cork in place and hold pressure, I drilled a hole through the lid of the bottle and the cork to create a hole for a pin mechanism that would be able to be pulled out to release the rocket, I connected some string to the end of the Allen key so I can pull the pin from a safe distance, the cost of this is low as I used scrap parts and pieces from around the house, the Allen key can be swapped out for any other material if it fits and is appropriate.
Extension material: I extended the rocket length by 6 Inches so I could be able to make the rocket level, it also made it so I can add reinforcements to the base of my rocket legs, I used some cardboard from a package but other materials can be used, ideally something that can get wet, costings for this will be low at £0.10p worth of materials.
