Introduction: Bouncy Rockets
This is part of a series of Instructables intended for teachers about educating students in the classroom around making and tinkering. For more about the details of this project, check out our blog.
There are multiple variants of safe in-class rockets out there, but this one favors quick iteration, can be performed indoors and uses simple, readily available materials. As some background, I saw a video with someone testing out a toy which used a bouncy ball to launch a nerf-gun style foam rocket. It seemed really cool, incorporates some aspects of transference of energy, the physics of flight and gravity. The toys are rather expensive for what they are, so I thought it would be easier and more fun to make your own. It is!
These rockets fly pretty high depending on your design, up to 12 or 15 feet (4-5 meters) if dropped from just a standing position. Dropped off of a chair, staircase, or higher they will travel even higher!
Step 1: Materials and Tools Needed
The materials required for this are pretty easy to scare up. You'll need:
- A bouncy ball. Cheap, hard ones are not as good. I tried a few variants and settled on some high quality ones from Toysmith.
- Straws. Typical 1/4" diameter drinking straws. Make sure they aren't jumbo or coffee stirrers, and it doesn't matter if you get the straight or flexible variety. Grab them from the grocery store - usually less than $2 for 100 of them, which is more than enough.
- 5/16" x 18 tpi hex nuts. I grabbed these from McMaster Carr, don't go crazy though because your local hardware store will have them for relatively cheap. Other thread varieties will work (24 tpi) so don't worry too much about the specific on these. A box of 100 will be $5-$7, enough to make about 100 rockets.
- 3/16" dowel. I got these from JoAnn fabrics that were 12" long and cut them in half. Your hardware store should have them as well in 36" or 48" long varieties.
- Hot glue gun and hot glue sticks
- Drill bit and drill - I used a drill press because I had to do about 600 of these, but your standard drill will be fine with a 3/16" bit. If you have anything between a 3/16" to 1/4" drill bit, it should work well.
- Paper, craft foam, cardboard, etc. for fin materials
Optional: If you are doing this with a large class of kids, I highly recommend safety glasses for the launch phase, as these rockets fly around like crazy and would be bad to get caught in your eye.
Optional: Tape is also a good way to attach all the components to the rocket, it's just not as durable as hot glue and trickier to make work.
Step 2: Make the Launcher
Making the launcher for the bouncy rockets is relatively simple. You only need one of these to launch as many rockets as you can build. First, take your bouncy ball and remove any stickers, packaging, etc. Get your drill bit secured in your drill or drill press. You will want to hold the ball securely, so maybe put it in a vise (but not squeezed so hard that it will break when you drill into it). Use common sense with this part, as it is really easy to drill a hole in your hand when trying to drill a spherical object that wants to roll away!
Fire up your drill and find a spot on the bouncy ball that is as far away from any molding seam as possible. Don't drill into the seam, as that may split the ball. Drill about 1/2 way through the ball. For instance, mine were 1-1/4" in diameter, I drilled about 3/4" into the ball. A little more or less is okay, just don't go all the way through or more than 3/4 of the diameter of your ball or putting the stick into it will blow through the other side and ruin the bouncy ball. This is easier if your bouncy ball is clear. If not, measure the distance you want to drill and put a piece of tape on your drill bit to mark the depth.
Once your hole is drilled, get your dowel. It's helpful to have a dowel that is less than 10" long, since that is the length of a typical drinking straw (some might be 8" - it just depends on your source). Cut the dowel to length - I recommend 6" but you can fudge this measurement without sweating anything. Once you have a length you like, simply stick the dowel in the hole of the bouncy ball you just made. For extra refinement, bevel the edges of the dowel with a sander, but this step can be skipped.
If you drilled a bigger hole (1/4") or your ball is really hard rubber, you may want to add some glue like hot glue or E6000 to the hole. Softer rubber or tight clearance here will hold the stick just fine. You're go for launcher!
Step 3: Make a Straw Rocket
Now for the fun part. Get one of your drinking straws and cut it to a length you like. I recommend making it shorter than the launcher stick just enough so you can pinch the stick for the launch drop, as shown above. You are welcome to make them way shorter or longer, but longer will make it harder to launch. 5" or so is about right for a full-size rocket. Mini rockets that are about 1" high with tiny fins can really fly far, too!
Once you have a rocket body you are happy with, it's time to cut out some fins. Add 3 or 4 or 10. I like craft foam for these because it is stiff and also durable for multiple launches, but cardboard, card stock, plain paper, cereal boxes, etc. will work just as well. Make them whatever shape you want - try making a moustache, heart, octagon, or anything else crazy!
IMPORTANT: DO NOT allow hot glue to get inside of the straw during this part or any other. If you do, it will make it so your rocket does not easily slide off the launcher and you'll be grounded on the launch pad!
After you've decided on your fin shape and cut it out of your desired material, it's time to glue them to the rocket body. If you've used a thick, firm material simply add glue to the end of the fin that you want to glue to the rocket body and allow it to cool before removing your finger. If you have a thin material like construction paper, make a fold as shown above and add glue to the flat side of the fold. Press this against the straw and allow it to cool. I recommend doing it this way instead of gluing directly to the straw, as the heat from the hot glue gun may deform the plastic of the straw.
Once you have your fins attached, you can optionally add some weight to the rocket with the hex nuts. They will fly fine without the weight, but it does make them fly further and with more stability (dependent on fin material, size, etc). Put some glue on the outside part of the straw that you would like to add the weight to. Push the hex nut onto the glue you just added and allow it to cool.
Alternatively, if you want to adjust where the weight is, grab some tape of any kind and build it up around the straw so the hex nut has a friction fit onto that part of the straw. Try experimenting with sliding the hex nut up and down the rocket body to see what effect this will have with flight.
Step 4: Ready for Launch!
Once you have crafted your launcher and a rocket (or 50 rockets - they're cheap so make a bunch of different designs!), it is time to launch. Simply slide your rocket over the stick in the bouncy ball, and drop it with the bouncy ball facing the ground. Try dropping it from different heights like a chair, or safely out of a 2nd story window, etc. If you are doing this with a large class of kids, I highly recommend safety glasses for the launch phase, as these rockets fly around like crazy and would be bad to get caught in your eye.
Step 5: Further Questions and Standards Addressed
- Where does adding the weight make the rocket most stable?
- Where will adding the weight make it tumble the most, or land on its bottom every time?
- How does the number of fins affect the flight of the rocket?
- How does the shape of the fins change the flight of the rocket?
- What can you do to make the rocket tumble more? Less?
- What will happen if you make a really long rocket (glue two straws together, for example)?
- What happens if you make a really short, tiny rocket?
- What other items might you add to the rocket to make it more stable?
- How could you make the rocket more aerodynamic?
NGSS 5th Grade Standards addressed:
Largely engineering design, 3-5-ETS1.
Influence of Engineering,Technology, and Science on Society and the Natural World
3-5-ETS1-2. Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
3-5-ETS1-3. Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved.