Marble Drop

This is a crazy machine project for my Cub Scout Pack. This week we are making marble drops out of rolled up paper tubes, rubber bands, a tongue depressor and a paper clip. There is spring loaded release at the to of the first marble. The marble rolls down the first run and jumps across an open space to the catch of the second run. You can see it in slow motion in the video.

To build this project you will need:

11 sheets of paper

1 glue stick

1/4" dowel 12-15" long

pvc electrical conduit 1/2" id, 13" long (approx. 3/4-7/8" od)

a bunch of rubber bands (I'm using 2-1/2" x 1/16")

The dowel and conduit are used to form the paper tubes.

You will need 11 sheets of paper.

The supports are formed using the 1/4 dowel. I had mine from previous Cub Scout projects: we bought them at Lowes.

For supports you will need 4 @ 11" long, 5 @ 7-1/2" long, and 5 @ 3-1/2" .

Cut 5 sheets of paper into 2 pieces each to get the 7-1/2 and 3-1/2" lengths: each sheet will give you 1 @ 7-1/2"x8-1/2 , 1 @ 3-1/2" x 8-1/2".

To form the tubes I start by rolling the paper all the way up on the dowel. Start with edge of the paper the same length as the tube you are making.

If the edges do not line up nicely once you have rolled the paper all the way up, you can slide the tube off of the dowel and tap it on the table to even out the edges. Then put it back on the dowel.

Once the paper is rolled all the way up, keep rolling. It will tighten the paper around the form. Keep rolling until the paper is tight around the form, then un-roll it a little more than 3/4 of the way. Be careful to keep tension on the paper so as not to loose the tightness around the form.

Re-roll the paper tube gluing as you go. Start by place a line of glue (using the glue stick) along the whole length of the form for a couple of inches up the roll. Make sure to keep the tension on the form so the paper does not un-roll before you glue it. Once you get to the end of the paper, keep rolling to make sure it's tight.

The marble runs are formed using the conduit.

You need 2 marble runes @ 8-1/2" (1 sheet each).

Each joint is made by "lashing" two tubes together using a rubber band.

Start by looping the rubber band over one of the tubes.

Cross the tubes at right angles.

Pull it under the other support and back over the first.

Take up the slack on the rubber band and give it a twist.

Loop the rubber band back under the other support and to the side of the first support.

Pull it over the end of the support to lock it in place.

The rear supports are made from 2 @ 11" tubes for the uprights and 3 @ 3-1/2" tubes for bracing.

The top 2 cross braces form the rear top support for the first marble run. They should be spaced about 1"-1-1/4" apart. Since everything is held together with rubber bands its easy to adjust things as you go.

The front supports are made from 2 @ 7-1/2" tubes and 2 @ 3-1/2" tubes fro bracing.

Use 2 @ 7-1/2" tubes for the bottom braces.

Use the last 7-1/2" tube for one side of the top brace.

The other side uses the remaining 2 11" tubes. These are placed about 1-1/4" apart to provide support for the second marble run.

Depending on which side you place the long (11") lateral supports will determine which way the final marble run faces.

The first marble run is held in place by the 2 top cross braces on the rear support, and a rubber band on the front support.

The second marble run needs a catch cut into it. Cut an opening in the 2nd tube about 1-1/2" long 1" from an end of the tube. The opening should be no more than 1/2 the diameter of the tube.

To find the right placement for the second run slide the 1/4" dowel down the first marble run and line the second run up to it.

To attach the second run in place, loop a rubber band between the two lateral supports. Twist the rubber band 2 times and separate the center twist with your fingers. Slide the end of the tube with the catch into the opening.

Attach the tongue depressor just below the marble run on the rear support. Start by lashing one side of the tongue depressor to the left side of the rear support.

Loop a rubber band around the top of the right support and around the bottom of the tongue depressor.

This will provide the counter pressure to the rubber band pulling on the release pin (next step).

Mark the underside of the marble run where the tongue depressor cross is it. This will be where the paper clip release pin will go into the marble run.

Remove the marble run and poke a small hole for the release pin along the line your just marked. Be careful not to crush the tube.

The release pin is made from a paper clip.

Start by unfolding the long edge of the paper clip.

Take the short edge and rotate it out 90 deg. This will leave 2 loops in the paper clip. One will hold the rubber band providing tension, the other will rest on the tongue depressor (next step).

Start by sliding the release pin into the hole made in the marble run.

Loop a rubber band over the bottom of the release pin.

Slide the release pin over the tongue depressor so that it sits on top of it.

Loop the rubber band over the 2 lateral braces below it.

Add a marble and your done!

To make it work pull down on the tongue depressor.