2021 SECC Division A Project: Marble Machine

Tournament Rules:

You must follow all of these building rules. Entries that do not follow these rules will be disqualified.

  1. Your machine can only be built from items listed in the Materials and Equipment section. No other materials are allowed.
  2. Your machine must be entirely gravity-powered. This means that you cannot touch the machine during operation and the machine cannot have any electrical or motorized parts.
  3. Your machine must fit on a 2 ft by 2 ft piece of cardboard. This piece of cardboard can only serve as a base and must remain flat. You cannot fold the cardboard or cut off smaller pieces and use them as parts of your machine. You are allowed to tape your machine to the cardboard.
  4. The machine must collect the plastic spheres in two separate 16 oz cups. These cups must be removable so you can easily count the spheres. They cannot act as structural supports for your machine or otherwise be permanently attached to the machine.
  5. You must start the test with a single 16 oz cup containing a mixture of 25 each of 6 mm and 10 mm spheres. While you can pour the spheres into the machine as slowly or as quickly as you would like, you must pour them in one continuous motion. You cannot pause during pouring.


When building your machine, you can test it and modify your design as many times as you would like. You can always re-test to try and get a higher score. There is no limit on the number of tests you can do, but you can only execute the procedure one time for the contest during the competition to calculate your score. Follow these steps to execute the procedure:

  1. Use a permanent marker to label three 16 oz cups A, B, and C. Cup C will contain the starting mix of spheres. Cup A will collect the 6 mm spheres, and cup B will collect the 10 mm spheres.
  2. Put a mixture of 25 each of 6 mm and 10 mm spheres into cup C.
  3. Have a judge get ready with a stopwatch, and count down “3, 2, 1, GO!” As soon as the judge says “GO!,” you can start pouring the spheres into your machine.
  4. Do not touch the machine during the run. For example, do not reach in to dislodge a sphere that got stuck, or to re-tape part of the machine that broke.
  5. The judge should stop the stopwatch as soon as the last sphere either falls into a cup or falls out of the machine. You do not need to keep the stopwatch going until spheres that fall out of the machine stop moving. For example, if the last sphere falls out of the machine, bounces off the table, then rolls across the floor, you can stop the stopwatch as soon as it falls out of the machine, you do not need to keep the watch running until the sphere stops moving on the floor.
  6. Remove cups A and B so you can count the number of each type of sphere in each cup. See the scoring section for more details.


The score for your test run is calculated using this equation:

Total score = 200 × (Correctly sorted spheres − incorrectly sorted spheres) − (50 × Time in seconds) + (100 × Judges’ Score)


  1. “Correctly sorted spheres” means spheres that were sorted into the correct cups (6 mm spheres into cup A, and 10 mm spheres into cup B). These spheres increase your score.
  2. “Incorrectly sorted spheres” means spheres that were sorted into the incorrect cups (10 mm spheres into cup A, and 6 mm spheres into cup B) or not falling into the cups. These spheres decrease your score.
  3. If your stopwatch displays time in hundredths or thousandths of a second, round your time up to the nearest tenth of a second (e.g. 10.43 seconds becomes 10.5 seconds).

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