Introduction: Zipline Racers - Detailed Instructable Remix

About: We're the spectrUM Discovery Area, a hands-on science museum in Missoula, MT. We have a physical museum located within the Missoula Public Library, but also create science kits, lead teacher professional devel…

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 this video on YouTube.

This is a remix of another Instructable by LanceMakes from which I got this idea. Check out that Instructable for a great video about these amazing devices, and much thanks to LanceMakes for this creative, original idea.

Propeller-powered ziplines are a great entry point into flight and propulsion using simple, cheap materials. Participants will make a propeller-powered device that zooms down a string at a relatively high speed. Ideas and outcomes addressed are the physics of flight and propulsion, kinetic/potential energy storage, and the challenges of engineering structurally robust components.

Step 1: Materials Needed

To build these ziplines you need some variation on the following supplies:

  • Craft sticks/popsicle sticks. They are available at most craft stores, or online. Get the regular ones, not jumbo. I used these.
  • Rubber bands. You can buy hobby-grade 8" rubber bands at hobby stores, but I found that office supply stores have 7" bands that are way cheaper and work just as well. #117B is what you'll need to look for.
  • Hot glue and glue guns. Like, a lot of hot glue if you're doing this with a class, you'll burn through the stuff real fast.
  • Large paper clips. I found that vinyl coated paperclips have the least friction when placed on the zipline.
  • 5" or 6" hook-nosed propellers. You can find variations at most hobby stores, I found this supplier that was great for bulk purchases. It is important to get the hook-nosed variety so they fit over the craft sticks.
  • Fishing line or kite string. I tried multiple types of line/string, mason's line worked okay but fishing line had the least friction. As a bonus, I used an old fishing reel mounted to a stand as the zipline.
  • Paper or craft foam.
  • Masking tape

Optional Additional Supplies:

  • To measure the speed/distance traveled of the racers you will need timers, 30-foot measuring tapes, a helper, and paper/pencil and a calculator.

Step 2: Quick Introduction to Ziplines and Flight

Building of the ziplines with a full class of 25-30 5th graders (10 years old, roughly) took about 1.5-2 hours. This included having them each build a zipline from scratch, individually, and having them test, modify, and measure the speed.

My spiel for introduction is to ask what the kids know about ziplines already. Have one or two describe what a recreational zipline is if they are familiar (a person gets in a harness, attaches to a cable, and moves along this zipline). What is powering the person in this instance? Gravity, typically. We are going to use propellers that are spun by rubber bands for our propulsion. Define propulsion for the kids, or have them make guesses and interpret this word. How does a propeller work? It spins, pulling the object through the air, or forces air over a wing that provides lift. Talk about lift if you are comfortable explaining this concept accurately.

Step 3: Step 1: Building the Base

I made a few of these models for the kids to duplicate so they could have initial success with their models. Variations are possible, this is just what worked best.

  • Starting from the front, there are two craft sticks glued and taped together. These are then wrapped somewhat thickly with masking tape at one end for the propeller to fit over. If you're only making one, feel free to glue the propellor on but I wanted the kids to reuse the propellers for multiple ziplines if possible.
  • Glue one more stick halfway onto the two you just glued together for the nose, opposite where the propeller will be mounted.
  • Glue another stick onto the other side of the stick you just glued onto the two wrapped together. This will make the base of your zipline two craft sticks end-to-end long, which is about 8".
  • Bend a paperclip into an "L" shape, and put a bunch of glue on the very end of the craft stick opposite the propeller. Mush the larger part of the paper clip into the glue. Allow the glue to cool and harden, then wrap this part with tape for extra strength.
  • Hook the rubber band into the hook of the propeller, then onto the small part of the paper clip that is protruding from the other end. You can bend the paper clip part closed to keep the rubber band in place, but it's not necessary.
  • That's it! Your base is complete.

Step 4: Step 2: Build the Top

There is no right way to do this step. As with most making and tinkering, your imagination and individual designs should guide this part. A few tips:

  • You need to build the top high enough so that the propeller doesn't catch the zipline. At least one craft stick tall (4" or so) will work well.
  • There need to be at least two attachment points for your paper clips to hang the device from the zipline. Only one will make the whole thing spin around on the zipline and will just make a mess. 3 is fine, but the more you add, the more friction you will induce on the zipline.
  • Triangles are stronger than squares!

Step 5: Step 3: Test and Improve

Now that you've built your zipline, it's time to give it a test. Lash a piece of string between two solid structures above the ground by at least 3 feet. The string should be fairly taught like a guitar string. You will probably need at least a 20-30 foot run, maybe more.

Wind the propeller CLOCKWISE for a fairly long time. Your rubber band should double up on itself like in the photo above.

Hold your propeller in place - don't let it go or it will smack your fingers, and that will hurt. Ensure that the zipline is clear all the way down and hang it on the line by the two hooks.

Stand aside and release the zipline - whoa! Try adding paper or foam to the middle. How does this change the flight?

Step 6: Step 4: Measure the Distance, Flight Time and Speed

So, you want to know just how amazingly zippy your zipline racer is? Follow these simple steps to measure and calculate its speed.

  • You'll need a helper to time the duration of the flight for this step. Have them stand somewhere alongside the zipline string so that they can see the zipline start and stop.
  • Get your zipline all wound up and hold it on the string ready to launch. Have your timer ready.
  • Do a countdown to launch so that your timer knows when to start.
  • The second you let go of the zipline, have your timer start their stopwatch.
  • Your timer needs to stop the stopwatch the instant the zipline comes to rest.
  • Take your measuring tape, and measure the distance that the zipline flew from start to finish. It is more accurate to measure from the back of the zipline body at the start to the back of the zipline body at the end (i.e. ensure you're measuring from the same point of the zipline's body with this step so you aren't adding distance that was not actually traveled).
  • Speed is just time divided by distance. Miles per hour or kilometers per hour are measurements of speed, for example. We're doing feet or meters per second in this measurement. If you want to translate your distance into miles per hour, divide the seconds that it took the zipline to fly by the feet it flew to get feet per second and multiply by 0.681818. If your measuring tape only does number of inches, it's a bit easier in that you don't have to convert feet/inches to decimal. The conversion is different for this: see the example handout below or the .pdf in this step for a way to record the data and convert using inches. For kilometers per hour from meters per second, multiply by 3.6.

1. How far did your racer travel? ____________Inches
2. How long was the flight of your racer? _________Seconds

3. Divide the distance of your flight by the number of seconds.

(For example, 100 inches / 2.3 seconds).

Write that number here:__________Inches per Second

4. Multiply the number in step 3 by 0.05681.

5. Write that number here: __________Miles per Hour Whoa, that’s fast!

Step 7: Final Step: Questions for Reflection

Here are a few questions to explore while doing this activity:

  • How does changing the weight, amount of rubber band windings, etc. change the speed of the zipline?
  • What does adding paper to the body of the zipline do to its aerodynamics?
  • How can you build a faster zipline? A slower one that carries weight?
  • How do different designs fly? For instance, some will fly very fast but not as far, others travel slower but further. What is going on in these designs to induce these different outcomes?

Reflect on the following:

  • What things did you learn while creating these devices?
  • Knowing what you do now, how would you modify your design or create a new design to achieve a different metric (faster, prettier, smaller, etc. zipline)?
  • What problems did you encounter when making the zipline? How did you overcome those challenges?
  • What different materials might you use to make your zipline behave differently?