Musical Marble Run
What Will You Learn?
See how many different kinds of sounds you can create by letting marbles roll and drop through your marble run!
Marble runs are fun to watch—and when you add your own bells and shakers, they’re also fun to listen to! This barebones marble run may seem simple, but it’s got what robotics scientists call a “programmable body.” That means you control the sounds it plays by how you place the ramps and noisemakers. Use the power of gravity and the concepts you learned about how instruments such as idiophones work to make it play faster or slower, softer or louder, and higher and lower. That’s how you turn a basic toy into a real Musical Invention!
Musical Inventors: Wintergatan
Martin Molin of the Swedish band Wintergatan (www.wintergatan.net) is known for the gigantic hand-powered marble music machine he designed and built out of wood, LEGO pieces, plastic tubes, funnels, rice, and drink coasters. When Molin cranks the machine up, 2,000 marbles are pulled to the top on little elevators. He programs the machine using belts made of LEGO Technic pieces. The pins open gates that allow marbles to drop onto the machine’s built-in vibraphone (a xylophone with a wavering sound), drums, cymbal, or bass guitar in time with the music. Wintergatan’s wildly popular music video featuring the Marble Machine has racked up more than 40 million views on YouTube (youtu.be/IvUU8joBb1Q).
Be careful when cutting the bamboo skewers—sharp bits of wood can go flying off in unexpected directions. Protect your eyes by wearing safety glasses.
Children who are not experienced with hot glue guns should get adult assistance. The heated tips and the melted glue can cause minor burns. Always use a piece of heavy scrap paper or a silicone pad under the hot glue gun to avoid damaging your work surface.
Cut the Skewers
The bamboo skewers you are using for your building material have sharp points. Use the wire cutters to snip the points off. Wear eye protection and point the skewer point away from yourself and other people before you snip.
Also cut several skewers into pieces 1½ inches (4 cm) long. Set these aside where you can grab them as you need them.
Create a Sample Set of Tracks
The marble run consists of two towers that hold up rows of slanted tracks. The tracks have a narrow end and a wide end. At the narrow end, the two tracks are just far enough apart to allow the marble to roll along them. At the wide end, the marble is able to slip through to the next level down. To help you figure out the measurements of your system, create a sample set of tracks.
Take two skewers. Lay a marble on the work surface. Line up the skewers on either side of the marble. This is the widest point between the tracks. You should be able to lift the skewers up easily, without rubbing the marble.
Take one of the short pieces of skewer you cut and glue it across the two tracks to hold them in place, about ¼ inch (6 mm) from the ends of the tracks. The other end of the skewers should be almost touching. You can use the thin edge of a tongue depressor as a spacer while you glue another short piece across the other end.
Make Tower Supports
Take a skewer and poke the pointed end into a small bead (preferably a bead with a flat bottom).
Secure it with a little hot glue. (Use a piece of scrap wood to wipe off any excess glue that leaks out.) Let it cool.
Repeat with three more skewers, for a total of four.
Assemble the Side Towers
Now it’s time to assemble the side towers. They are made up of two of the sticks with the beads, with a tongue depressor as a base.
To figure out the proper width of the tower, take two of the tower skewers with the beads on the end and lay them down side by side. Fit the wide end of your sample track around them. Spread the tower skewers apart until they touch the inside of the track skewers.
Glue a crossbar (short piece of skewer) across the two tower skewers to hold them in place, right above the beads. Check to see that the narrow end of the sample track fits inside the tower. If it does, then glue the bottoms of the beads onto a tongue depressor. If not, adjust everything by carefully peeling apart the glued sticks and regluing them in the proper positions.
Repeat with the other tower—but the crossbar for the second tower should be about 1 inch (2.5 cm) higher than on the first tower. Measure the position of the higher end of the track and mark it on the tower in pencil before gluing.
Make the Bottom Set of Tracks
To make the bottom set of tracks that will help support the frame, set two skewers inside the tower sticks, resting on the crossbars. Leave about ½ inch (12 mm) of the skewers hanging off either end. Attach the skewers to the crossbars with hot glue. Before going on, roll a marble down the tracks to make sure they’re tilted enough— if not, carefully remove the higher crossbar, raise or lower that end of the tracks, then reglue.
Next, glue crossbars onto the tops of the tower sticks, making sure that the width of the towers stays the same at the top and the bottom.
Connect the tops of the towers by gluing two skewers on the outside of the towers, just below the top crossbars.
Test again to make sure a marble can fit between the skewers at the top of the frame.
Add Tracks Inside the Frame
You already have the bottommost tracks in place. To build the next level up, take your sample set of tracks and insert it between the towers. Follow the guidelines below to position it correctly, then mark the position of the ends on each tower.
Remove the sample and glue crossbars onto the towers at the marks.
When they are dry, rest two skewers on the crossbars. At the lower crossbar, glue the skewers to the outside of the tower. At the higher crossbar, glue the skewers on the inside of the tower.
Test the new level with a marble. Then continue adding on levels the same way until you reach the top of the frame.
Now you can add tracks inside the frame to make the different levels. You can control the speed of the marbles by altering the slope of the tracks. The steeper the angle of the tracks, the faster the marbles will roll. The slant will also determine how many sets of tracks you can fit into the framework of the marble run. The sample system in the photos has six sets of tracks. Here are some tips to keep in mind:
- Like the sample track that you made, every set of tracks has a narrower end, where the skewers are glued to the inside of the towers and a wider end where the tracks are glued to the outside of the towers.
- The narrower end of the tracks is always higher than the wider end.
- The tracks will zigzag—on one level the tracks tilt down to the left, the next set tilts down to the right.
- The wide ends and the narrow ends of the tracks alternate— the wide end of one level sits above the narrow end of the level below it. The marble will drop from the wide end of one level to the narrow end of the level below it.
- Use your sample set of tracks to figure out where the high and low ends of your track will be connected to the towers. You can vary the slope of each level, or just make them all the same. If you want your marble to bang into or bounce over noisemakers, tilt the track so it is a little steeper. That will give your marble more speed and keep it from getting stuck.
- You can also add speed by increasing the distance the marble has to drop between one level and the next. The drop should be at least ½ inch (12 mm), but you can make it as much as 2 inches (5 cm).
- Be sure to leave enough room between levels so you can hang noisemakers like keys and washers.
Add Guard Rails
To keep the marbles from falling off the sides of the tracks, make “guard railings” by gluing skewers on the outside of the towers, a little above each track. (They should be about half as high above the tracks as the marbles are tall.)
Once your marble run is operating smoothly, you can start to add noisemakers. These can be attached to crossbars glued to the underside of the tracks where needed. Be sure to test them before you attach them permanently to make sure they don’t slow or stop the marble along the track. Here are some ideas:
- Hang a bell over the track. If needed, make the clapper longer so the marble hits it as it rolls underneath.
- Hang keys, metal washers, or recycled mini wind chimes from above.
- Make a clackity “raft” with mini craft sticks. Line up the sticks, attach two sticks across the raft on both sides, above and below, and tie these sticks together with string. Hold the whole raft in place by tying another craft stick to a crossbar loosely fastened across the tracks.
- Attach a string of beads between the tracks just high enough for the marble to bump along as it rolls downhill.
- Save large bumpy noisemakers— such as large wooden beads or metal bottle caps— for the spot right below the drop from one level to another. That will give marbles enough extra momentum to get over the rough spots.
- Use a small spoon to make a seesaw on a crossbar below the track that lowers the marble to the next level. Hold a loop of stretchy string or a rubber band under the crossbar and hook it over the ends from underneath. Then take the handle of the spoon and thread it between the stretchy string and the crossbar, with the string on top. Balance the spoon so that a marble can roll over the handle and drop into the bowl of the spoon, where the weight will tip it downward until the marble rolls out onto the next level. The elastic makes the spoon return to its starting position, ready for the next marble.
- Be sure to end the marble run with some kind of noisemaker, such as a wind chime laid crossways across the railings.
Making Music out of Noise
Part of the challenge of building a Musical Marble Run is getting everything to work right. The other part is getting it to create clacks, bangs, and bongs that sound musical! Remember that you can “program” your marble run as you design it. First, you can control the tempo, or speed, of the music by controlling how fast marbles roll along. You can also control when sounds occur and in what order by the way you arrange the various noisemakers. As you experiment with different placements, keep in mind what kind of notes and rhythm you want your marble run to play. That’s how you turn a toy into a musical invention!
Getting the Best Sound from your Marble Maze
When adding noisemakers of various kinds to your marble run, remember what you learned about standing waves on an idiophone: in order to get the best sound, you should fasten the vibrating piece where the nodes—the points that stay still—occur. For wooden and metal bars, the nodes for the fundamental frequency (the main pitch you hear) are a little less than one quarter of the way in from either end. If it’s not easy to fasten the bar at that point, attach it as loosely as possible so it can vibrate freely.
About the Book
Explore the physics of sound with hands-on projects that anyone can make! From simple flutes to cutting-edge electronic musical gloves, such fun kits as littleBits and Makey Makey, to the sonic opportunities found in ordinary household items, Musical Inventions will get you making your own music using your own instruments.