Rocketry is one of the most fun and engaging pastimes a person can undertake. In terms of educational benefits, there are few tools out there that can as effectively be used to teach an entire STEM (Science Technology Engineering Mathematics) curriculum. Rocketry can easily be used to teach forces & motion, algebra, trigonometry, aerodynamics, and a host of other essential subjects.

The drawback is that it can be somewhat costly to get started, and costly to maintain if you must depend on purchasing materials. I am a Technology Education teacher in a small New England public school district, and I needed a way to be self-sustaining (very inexpensive) for my rocketry lessons. For the hobbyist, or parent, being able to create a rocket and launch it is an immensely gratifying experience, and keeping that experience inexpensive is always a plus. This article depends on access to a 3D printer, but they are becoming both more common and less expensive every day.

Step 1: Materials

You will need:

-Access to a 3D Printer (I used a Makerbot Replicator 5th Gen with standard settings)

-A Free TinkerCad Account

-A LOW temp hot glue gun (It MUST be a low temp glue gun)

-Low temp glue sticks

-An empty PLASTIC soda bottle (16oz, 20oz, 1 Liter, or 2 Liter)

-A tailor or seamstress measuring tape (or a strip of paper you can mark)

-A Black Sharpie

-A small piece of sand paper (I used 100 grain)

-A Ping Pong Ball

-15cm or 6 Inches of kite string

Step 2: Collect Design Data

Here you will need to collect your data in order to figure out the dimensions of your nose cone and fins.

Note 1: If you are just going to use my .stl files, and have a 20 oz bottle you can skip this step and the next step after downloading and printing the attached file.

Note 2: Your life will be easier with this project if you use Metric measurement.

Throughout this step and the next we will be working with specific measurements, usually in Millimeters. Don't feel like your measurements need to be incredibly exacting here. The more exact you are the better your rocket will fly, but the forces involved with bottle rockets of this type are fairly minimal in comparison to even to lowest power model rockets. With the lower force in mind, feel free to fudge the numbers a bit.

Steps:

Take the empty soda bottle you have chosen and measure the Diameter (D) at the bottom of the bottle, when you move on to design your nose cone and recovery device this measurement will be your base measurement. Write it down.
Take the empty soda bottle and measure it's total current height. This measurement will be used to determine the length of your nose cone. Write it down.
Use your Tailor tape or strip of paper to measure the circumference of the bottle at the area where the label once was. (If you want to be super cool you can figure out the circumference mathematically using the formula: circumference is equal to twice pi multiplied by radius or C=2Pi*r). This measurement will be used when you attach your fins. Write the circumference down.

*Safety Note-The below specifications apply ONLY to bottle rockets. Solid fuel model rockets have much tighter tolerances, and work with much greater force.

Most design elements of any rocket are functions of the rocket's Diameter, this is also true with bottle rockets, but the Diameter used is much larger than model rockets due using the soda bottle. As such we need to adjust our thinking a bit.

Determine the range of height your rocket can have. This measurement will take into account everything from your nozzle to the top of your recovery device. Your rocket can be between 5 times your Diameter and 10 times your Diameter (D5 to D10)
Determine the dimensions of your fins. This is where things seem tricky, but really aren't. First you need to know what the parts of a fin are called.
- The portion of the fin that attaches to the rocket is called the Root.
- The portion of the fin that is parallel to the ground is the Span.
- The Chord is the portion of the fin that is parallel to the rocket body but not attached to it.
Root Dimension (R)- The Root for this type of rocket should be at least half the diameter, but can be as much as equal to the diameter (R=D*.5 to R=D)
Span (S)- The Span should about twice the Root (S=R*2)
Chord (Ch)- The Chord can be anything from zero (meaning pointed), up to equal to the half the Diameter (Ch=D*0 to Ch=D*.5) if you decide to use a "Clipped" or "Trapezoidal" design (You can find info about common model rocket fin shapes by doing a quick web search)

bottle_rocket_lower_body_mount_and_fins.stl
Download View in 3D

Step 3: Design & Print Your Nose Cone and Fins

I used a conical design and a ping pong ball recovery system for a 20oz Soda Bottle here, and that is what the below instructions will generate for you. That said, there is no reason for you to do the same. There are a wide variety of rocket nose cone shapes available, and this aspect of your design will have a significant effect on your acceleration due to drag. Do a little online research, and use your own creativity to come up with alternatives.

*Note-These instructions assume some familiarity with TinkerCad. If you are unfamiliar with it, set up a free account and run through the tutorials available. It won't take much time, and you will learn a lot.

Log on to TinkerCad and open a new design.
Select the Wedge Shape from the Geometric Menu and drag it to the work plane.
- Refer to your data for Root and Span
- Change the Height of the wedge to your Root measurement
- Change the Length of the wedge to your Span measurement
- Change the Width of the wedge to 1mm
- Select the wedge shape you have just modified and copy it two times
- Congrats! You have just made your fins.
Go to the shape generators menu
Select Community
Browse until you find the shape called "Hi-Res Tube Funnel by Anthony Graglia"
Click the Star to add it to your Favorites
Browse a second time until you find the shape called "Tube by Elkniwt2"
Click the Star to add it to your favorites
Go to your favorites menu, and drag the Funnel shape to your work plane
- Using the slider, change your Diameter Bottom option to a little greater than the Diameter of your bottle in Millimeters
- Using the slider, change your Diameter Top option to about 20mm
- Using the slider, change the Wall Thickness option to about 1mm
- For a 20oz Soda Bottle your Height will be about 50mm (For other bottles you will have other heights, you will have to see what looks right to you. Starting with your Height being Equal to your Diameter is a good way to begin.)
Go to your favorites menu and drag the Tube shape to your work plane
- Using the slider, change the inner Diameter option to within about 1mm of the outer Diameter, which should be 20mm
- For a 20oz Soda Bottle I use a Height of 20mm, but you can use whatever height you want as long as the total height it fits within your height specification determined in Step 3.
Place the Tube on top of the Funnel (make sure the tube is connected to the tunnel)
Using the Align tool (in the Adjust menu) center the Tube with the Funnel
Select both shapes and group them
Go to your favorites menu, and drag another Funnel shape to your work plane
- Using the slider, change the Wall Thickness option to about 1mm
- Using the slider, change the Height option to about 5mm
- Your Top Diameter should be about 30mm, and the Bottom Diameter should be about 20mm
- Place the new Funnel shape on top of your already grouped shape
- Use the Align Tool to center the new funnel shape on your already grouped shape.
Select both shapes and group them.
Congrats you have now designed your fins, nose cone, and recovery system.
Click on the Design Menu
Click Download for 3D Printing
Select .stl
Open in your 3D Printer Software
Print

Step 4: Prep Your Bottle

Make sure you have removed the label and rinsed the bottle out with water.
Plug in the low temp hot glue gun, and load it with a low temp hot glue stick.
Divide your Circumference measurement by 3 (using metric you will end up with a decimal value, round the value down to the nearest whole number, it will be close enough).
At points 1/3 of the way around the bottle where the label was make small black marks with your sharpie.
Using a straight edge, extend your black marks so they reach from the top of where the label once was to the bottom of where the label once was.
Using sandpaper, roughen the area covered by the lines while being careful not to erase them.
Using sandpaper, roughen the sides of the humps at the bottom of the bottle.
Using sandpaper, roughen one of the valleys at the bottom of the bottle (which one doesn't matter).
Roughening these ares will allow greater adhesion of the low temp hot glue.
Lay one end of your kite string in the valley you roughened.
Put a glob of low temp hot glue over the end of your string that is in the valley.
Wait for the glue to harden (30 seconds to 1 minute)

Step 5: Attach Nose Cone Assembly

Pull the other (not glued) end of your kite string through your Nose Cone assembly. The string will run through the Nose Cone assembly from the larger end (bottom) through the smaller end (top). Pull the string tight.
Place globs of low temp hot glue on all of the humps you roughened.
Slide your Nose Cone Assembly onto the bottom of your bottle, making certain it is as straight as possible.
Wait for the low temp hot glue to cool.
Using a pocket knife trim any excess glue from the outside of your bottle.

Step 6: Recovery Device Assembly

Using a pocket knife or awl, poke a small hole (just larger than your kite string) in the ping pong ball.
Slid the unglued end of your kite string into the hole.
Put a glob of low temp hot glue over the hole and string.
Wait for the low temp hot glue to cool.

Step 7: Fin Assembly

(Repeat the following steps once for each fin)

Make a line of low temp hot glue on the Root of a fin.
Place the root of the fin on one of the black sharpie lines on your bottle making certain to keep the fin as straight and level as possible (extra points if you can create some manner of jig or device that assures your fins are mounted both straight and level).
Hold the fin in place while the low temp hot glue cools
Make a line of hot glue along each side of each fin.
Hold the fin in place while the low temp hot glue cools.

Step 8: Launch, Launch, Launch!!!!

These are the basic instructions for preparing to launch and launching a bottle rocket. I do not provide instructions for launcher construction as I already have a launcher, and several DIY and inexpensive versions are available online. Below is generally, how to launch a Water Bottle Rocket. Your specific launcher may be different.

Unscrew the cap and fill the bottle about 1/3 of the way up with water
Attach your Bottle Rocket to your launcher
Tuck the kite string inside the nose cone, and place the ping pong ball on top of the rocket.
Inflate to 50 PSI (this is the number I use, and I have not had a structural failure after 20 launches. I have used 80 PSI once with a 2 Liter bottle without failure. Go higher at your own risk)
Give a countdown from 5
Launch
Watch

Thank you for using my Instructable. I hope you enjoy launching your new bottle rocket!