Wave Viewer - a Mechanical Oscilloscope





Introduction: Wave Viewer - a Mechanical Oscilloscope

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What It Is:  This "wave viewer" creates a zoetrope-style effect that lets students see a snapshot of the waves on a vibrating string.

Learning Objectives:  A kid-powered, mechanical oscilloscope helps students explore wave phenomena.  Younger students can get a feel for the concepts of waveforms, frequency, and amplitude.  Older students can gain a greater understanding of the functions of an electronic oscilloscope (such as sample rate and amplification).

Grades:  Kindergarten through high school

Sources:  This project was begun as part of a university's science outreach program to an elementary school.  Inspired by the concept of "The Exploratorium Science Snackbook," which offers instructions on how to create classroom-sized versions of science museum exhibits, and by the amazing artwork of Norman Tuck, we created this project. 

Cost:  $20 - $30

Step 1: Parts and Supplies

For the main assembly:

   - A plastic bucket, 5-gallon size or similar
   - A lid to match that bucket
   - Black spray paint, suitable for use on plastics
   - Black elastic cord, about 24" long, and the thicker the better.  (This is available at most craft stores.)
   - A "lazy Susan" turntable bearing.  (I used a 6" version.)
   - White paint
   - A wide board to use as a base, about 12" x 18"
   - Two small eye hooks
   - A small cleat, such as the kind used for window blinds' sash cords
   - Three lengths of 1" x 2" wood, each about 16" long (or about the same height as your bucket)
   - Two triangles of scrap lumber, or two store-bought angle braces (see step 6)
   - Wood screws, 1" length or similar
   - Various nuts and bolts.  (I heartily recommend grabbing a $2 assortment of machine screws, rather than tracking down each part individually)

For the handle:

     Either Version One:  - One bearing from a skateboard wheel (see step 8)
                                        - One half-inch PVC pipe coupling
     Or, Version Two:  - A length of half-inch dowel (about 4" to 5")
                                  - A length of half-inch PVC pipe (of the same length as the dowel) 

Tools and other equipment:

     - An electric drill
     - Screwdriver
     - Pliers
     - Sandpaper
     - Paintbrush
     - Oven

Extra supplies for lessons:

     - Black electrical tape
     - Scissors
     - A black Slinky (the small kind sold as party favors by dollar stores)

Step 2: Painting the Bucket

The oscilloscope illusion results from watching a vibrating, black string against a background of alternating light and dark lines.  We'll need to create a black cylinder with white, vertical "pinstripes."

Paint the Bucket:  Flip the bucket upside-down and paint the outside completely black with spray paint.  (Make sure that you use a paint that's recommended for use on plastics.)

Add the Stripes:  Once the black coat is dry, paint twelve evenly-spaced, white "pinstripes" around the sides of the bucket.  Masking tape makes for super-straight lines;  aim to make them about 1/8" thick.

To help place the lines, I first made twelve white dots in a clock-face arrangement on the "bottom" (now "top") of the bucket, then used these marks as a guide when adding the tape and paint.

While the white stripes dry, move on the to next steps.

Step 3: Align the Bearing and Lid

The bucket needs to be able to spin freely on the base board.  We'll use the turntable bearing to attach the bucket's lid to the baseboard, and then install the bucket on the lid. 

1.)  Center the turntable bearing on the "inside" surface of the bucket's lid.  Mark where the bearing's holes go.  (A white correction-fluid pen is great for making marks on a black surface!)

2.)  Drill four holes in the bucket's lid in the places you just marked.

3.)  Find four machine screws that will match the holes in your turntable.  (For mine, 1/8" x 1" screws were a good fit.)  Test-fit the screws through the turntable and bucket lid to make sure that everything fits.  Then, remove the lid from the turntable, but leave the four screws in the turntable's holes.  (See the photos.)

Step 4: Attach the Bearing to the Base Board

1.)  With the four machine screws still protruding from the turntable bearing, place the bearing near the center of your base board.  (It's essential to leave those four screws in the bearing during this step, since there'll be no way to re-insert them once you've screwed the bearing down to the base board.) 

2.)  Mark where the four remaining holes in the bearing will be attached to the base board.

3.)  Attach the bearing to the baseboard with wood screws.

(Did you remember to leave those four machine screws protruding from the bearing?) 

Step 5: Attach the Lid to the Bearing

1.)  Hold the lid over the bearing so that the "inside" surface of the lid faces upward.  (This is so that you can attach the bucket to the lid.) 

2.)  Align the four holes in the lid with the four machine screws, and pull the screws up through the holes in the bucket.  (This part takes a bit of fiddling -- it helps to have a second pair of hands!)

3.)  Use the appropriate-sized nuts to attach the lid to the turntable bearing.  Use pliers to tighten the nuts as far as possible.

Step 6: Install the Frame

For this next step, we'll install a U-shaped frame of wood to the base board.  The height and width of the U-shape should more or less match the height and width of your bucket.  For me, this meant three 16" lengths of 1" x 2" wood.

1.)  If necessary, cut the three 16" lengths from a longer board.  (Hardware stores usually sell 6' lengths of 1" x 2" board.)

2.)  Use wood screws to attach the three pieces together into a U-shape.

3.)  Attach this U-shape to the front edge of your base board.  (Whichever edge you attach this frame to will become the "front" edge, so you might want to choose the edge that looks nicest.  Or not.) 

4.)  To add kid-resistant strength, you'll need to reinforce the corners of the frame.  You can either do this (as I did) with two triangles of scrap wood;  or, if you don't have any scrap wood (or would like a more-polished appearance), you could use some store-bought corner braces. 

Step 7: Attach Eye Hooks, Cleat, and String

To support the vibrating string, we'll attach two eye hooks and a cleat to the frame we just installed.

1.)  Attach a small eye hook to the inside edge of each tip of the U-shaped frame.  (The string will eventually be attached between these two eye hooks, so it's important that they be placed at about half the height of the bucket.  I found that 6" from the top on each side was a good height.)

2.)  Attach the cleat to one side of the U-shaped frame, near the bottom.  (I positioned mine on the right, since I'm right-handed.  The cleat will be used for winding up any extra elastic cord once the string is attached.)

3.)  Tie the length of elastic cord to one of the eye hooks, thread it through the other eye hook, and then wind any excess around the cleat.

Step 8: Make a Handle for the Bucket

The students will need a handle to spin the bucket, and it's important that the handle both turns freely, and is attached securely.  In this step, we'll go over how to build a sturdy handle from a PVC fitting and a skateboard-wheel bearing.  However, in case you can't easily find these parts, the next step will cover an alternate, simpler (albeit flimsier) handle.

1.)  Use a screwdriver to pry one of the bearings out of a skateboard wheel.  (Every skateboard wheel contains two bearings, and packs of cheap skateboard wheels are sold in the sporting-goods aisles of most Mart-style department stores.  If you have access to a hardware store that will sell you individual bearings, you might just go ahead and purchase one bearing with an internal diameter of about 5/16" or 8mm, and an outside diameter of about 7/8" or 22mm.)

2.)  Slide a 1/4" by 1" machine screw through the center hole of the bearing, and tighten it down with a nut.

3.)  To make a tight "press-fit" between the half-inch PVC coupling and the bearing, you'll need to heat the coupling in an oven.  I recommend about 10 minutes at 200 degrees F in order to soften the plastic.

4.)  Once the plastic is soft, you can press the PVC coupling onto the bearing until the bearing is flush with the end of the coupling.  (Be sure to use heat-safe gloves!)

5.)  Drill a 1/4" hole in the bottom of the bucket near the outside edge.  Slide the handle's screw through the hole, and attach it with a nut.

Step 9: Alternate Handle

In case you couldn't get a skateboard bearing, here's a simpler handle you can whip up from a piece of dowel and some plastic pipe.  However, this is much more prone to getting snapped off when twirled by young hands.

1.)  Cut an approximately 5" length of half-inch dowel. 

2.)  Cut a matching length of half-inch PVC pipe

3.)  Sand down the dowel until it will just barely fit into the pipe.

4.)  Rub all sides of the dowel thoroughly with a pencil to cut down on friction, then slide it into the pipe.

5.)  Similarly to the previous step, use a wood screw to attach your handle to the outside edge of the bottom of the bucket.

Step 10: Finish It Up!

Next, just press the bucket into the lid on the base board, and your construction phase is complete! 

For a few tips on how to use this oscilloscope as part of your lesson, see the next step.

Step 11: Lesson Tips

The Basics:  To use your wave viewer, have one student spin the bucket with the handle while another plucks the string.  

Cranking a bucket at high speed is a lot of fun for little hands, so you may want to encourage the "cranking" student to start slow, and gradually build up speed.

Most students' first impulse is to draw the string back like a crossbow, and snap it against the bucket.  While this does make a very satisfying "thwack!" sound, it doesn't let us see much about waves.  Be sure to ask the "plucking" student to pluck the string vertically, so that it oscillates up and down.

Once the kids have gotten over the initial "oohs" and "aaahs" of seeing their waveforms frozen in time, challenge them to see what changes will result from a few variations:  Can they make a small wiggle appear on the string?  How about a large one?  What changes if they spin the bucket slower and faster?  What's the slowest speed that will still make the illusion work?  What happens if they adjust the tension in the elastic string?

After that, it's assessment time!  Have the students identify which wave-related vocabulary terms apply to the oscilloscope.  Can they demonstrate a wave with a different amplitude?  A different frequency?  A shorter or longer wavelength?

Once they've explored the basics, you can have the students introduce a few new variations by tinkering with the oscilloscope:  if they replace the elastic string with a dark-colored slinky, can they demonstrate the difference between transverse (or "wiggle") waves and longitudinal (or "squish") waves? 

Challenges for Older Students:  Older students can use black electrical tape to obscure some of the white stripes on the bucket.  This is why we made twelve stripes;  it allows students to reduce the number of visible stripes while preserving even spacing. 

Have the students use the tape to leave, say, six evenly-spaced stripes, and crank the bucket at a certain speed.  Then, have them create three evenly-spaced stripes, and crank the bucket at the same speed as before.  How has their view changed? 

What happens if they use the tape to leave stripes that aren't evenly-spaced?  How does their waveform look when viewed against, say, three stripes in a row, with the other nine blacked out?

If the students (at high-school or college-level) are beginning to learn how to operate an electronic oscilloscope, have them identify which concepts/controls have analogs in the mechanical oscilloscope.  What is this scopes "trigger"?  Sample rate?  Gain? 

I hope you enjoy playing with your own oscilloscopes!  If you have any new lessons and experiences to share, please post them here!



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    Sounded like fun.

    Thanks so much for posting this! I saw an oscylinderscope at a science museum and have wanted to build something like it ever since. Voila, your project - affordable and simple to build. A few design changes I made: for the stripes, I bought white electrical tape and used a knife to cut the roll to a narrower width, then I taped the stripes on. Much simpler, and I can adjust them if I want. I made mine with three different plucking strings so that people can compare the wavelengths of strings with different pitches. I also purchased a small rotating caster wheel to use for the handle on top, but in the end I found that just pushing it with my finger works well. I think not having the handle will reduce wear and tear by avoiding rocking the bucket back and forth. (It's for kids to use!) Thanks! I am looking forward to using this in my classroom!

    very nice project, indeed!

    two years ago i've seen something similar but bigger - called "oscylinderscope" and built by norman tuck - and being very expensive - on an education show.

    we tried to build our own with a few girls during a day for musical projects at school using an ikea sideboard, some scrappy plywood and a broken guitar. the ball bearings we've used for the drum came from a pair of inline skaters, very close to your solution ;-)

    hopefully you can see the images attached here. one is as seen on the show while the other shows our nearly finished product. the girls painted it nicely afterwards and for two years now it's bringing fun to pupils walking along or waiting in front of it while physics teachers can use it for educational purposes with the wave theory.

    Musikschulfest 2010 693.jpgOszylinderskop Didacta K��ln 2.JPGOszylinderskop Didacta K��ln 3.JPG

    Wow! Your guitar-based oscilloscope looks great!

    I think that you should consider posting an Instructable on how to make your creation. I'm especially curious about how you attached the large drum to the skate bearings.

    How easily does the drum turn? Have you tried varying the width and spacing of the lines on the drum?

    Thanks for your pictures, and "Viel Erfolg!"

    hey chris,

    after painting a large circle on the plywood we cut the circled shape with a milling cutter. with the same tool we cut a bigger hole in the center - up to half of the plywood's thickness. that's where the bearings found their new home.
    close to the outer circle, around 5 cm away, the milling cutter cut out a notch, circa 6 mm deep. that's where later on a thin plywood will form the cylinder drum's bent tube wall.

    we put a threaded rod into the center of the bearings and fixed both sides with big washers and  screw-nuts. the rod was inserted through the big drum into the other side's bearings. the fixing procedure was the same here.

    between all that it was tricky putting the thin, white-striped and spray-painted plywood (as we use it in the back side of some cupboards) into the small notch and putting the whole thing into the ikea shelf type "ivar, 50 cm". during this process we had to fix all the screw nuts on the threaded bolt - also the ones inside the drum that should later fix the bearings from the inside. the strings are more or less tuned in major thirds.

    you can now easily turn the drum with one hand while the other is pulling the strings. the "oscylinderscope" has three nylon strings of different lengths and a foot pedal (where the strings are fixed) to enlarge the string length while enhancing the string tension. pulling the strings while pressing down the pedal makes you easily play the intro of deep purple's "smoke on the water" (as i heard it once when a girl played it on the oscylinderscope).

    unfortunately i don't now a lot about american and international copyright and related rights. so i wouldn't like to violate the owner's rights. as written above tuck norman has built the version i had seen first. but if you like i could send you some more detailed pictures of our finished product.

    please excuse my bad english - being an english learning pupil for me is a long time ago now!
    best wishes,

    Hi, Schaude:

    This sounds like it would be a lot of fun to build! I'd love to see more photos and hear more about how you built it.

    Have you considered making an Instructable for your creation?

    Thanks again!

    Very nice project. We did a smaller version using a soda bottle. You can see it here http://pontociencia.org.br/experimentos-interna.php?experimento=38 (instructions are in Portuguese only, but there are lots of images) or just look at the video (http://www.youtube.com/watch?v=XQQFP2Eq3Rc).

    Obrigado, almateus!

    Maravilhoso! I love the soda bottle version! The wide stripes and ease with which it can be rotated look to be real improvements. I'll try to make one of these this weekend.

    Now I'm hooked on this cool ("legal"?) Pontociencia website -- it's going to take me a long time to learn all of these projects.

    (P.S. -- "Ghost Riders" was an outstanding choice of muical accompaniment.)

    I am really glad you liked it! Pontociencia has the same idea as Instructables, even though it is just about experiments. Step by step instructions, videos, images. I should post some of our projects here, to get more american visitors (at least those that don´t mind the portuguese, like you!)

    Hey, almateus:

    Pontociencia is a great site! I've already found a bunch of experiments I'd like to try. It'd be appreciated if you made some posts to help English-speakers find more experiments.

    And thankfully, all the handy photographs make the experiments easy to understand for those of us who can't read Portuguese.

    (I mean, the only Portuguese I know is... um... "moqueca de peixe," and... "Anderson Varejao.")