Clear the Table

This video shows a game strategy using QTI sensors mounted on a 3-D printed scoop (Thingiverse thing #56016)


The Game

Name: Clear the Table

Objective: Find and push objects off of a low platform. The robot that pushes off the most objects in the least amount of time (up to 2 minutes) wins.

Challenges: Sensing the edge of the ring; using sensors to detect different kinds of objects; switching the robot between find-push-retreat modes; making a plow for the front of the robot; making the objects to push off the table; making the playing field platform.

The Rules

About the Robots

  1. Use a Parallax Boe-Bot, ActivityBot, Shield-Bot or SumoBot chassis-based robot.
  2. Contestants in each match must use the same servos to keep top-speed-capability similar:
    1. Parallax Continuous Rotation servos powered with regulated 5 VDC
    2. Parallax High Speed servos powered with 7.5 VDC
  3. This challenge is for autonomous robots — no remote control devices!
  4. You can use any combination of sensors to your robot that you want, such as:
    1. IR emitter/receiver object detectors (included in the Boe-Bot style kits)
    2. Whisker sensors (included in the Boe-Bot style kits)
    3. QTI Line Follower kit (QTI sensors included in SumoBot kits)
    4. Ping))) Ultrasonic Distance Sensor and Mounting Bracket Kit
    5. Sharp IR Sensor kit
    6. 2-axis or 3-axis accelerometer
    7. Vibra-tab sensors
    8. Color sensors
  5. You can make a custom plow attachment for the front of your robot:
    1. It can be made of any material that does not damage the table or the objects.
    2. It can be up to 12 cm wide, 12 cm tall, and can stick out in front of the robot up to 6 cm.
    3. It can be incorporated into the robot’s sensor system.
    4. It cannot be motorized.

About the Playing Field

  1. The playing field is table is 77 cm round and at least 5 cm tall.   The surface is hard and smooth with a black finish that does not reflect infrared light (such as matte paint, rubber, or vinyl). There is a white IR-reflective band around the edge of the top of the table, 2.5 cm wide.
  2. Eight objects are placed on the table for the robot to push off.  A timekeeper places the objects on the table in a random arrangement before each round.  See Game Variation Ideas below for object ideas.

About the Game

  1. The  timekeeper marks the start and end of each round, recording how long each one lasts (up to 2 minutes).
  2. A player puts a robot anywhere on the table, and when the timekeeper says “Go” the player starts the robot and cannot touch it again until the round is over.
  3. The round ends when one of these three things happens:
    1. The robot pushes all of the objects off of the table.
    2. The robot falls off of the table and touches the surface below.
    3. The timekeeper indicates 2 minutes are up.


  1. 1 point given for each object pushed off of the table.
  2. In the case of a tie, the robot with the shorter round time wins.
  3. In the case of a tie of both score and time, hold a rematch until there is a clear winner.


Game Variation Ideas

  • Easy game: Make the objects easy to detect — identical, white, smooth round cylinders with closed tops and bottoms, about 4 cm wide and 10 cm tall.  If using empty bottles or cans wrapped in copier paper, try putting a few pebbles in them so there is a little weight to them.
  • Hard game: Use a variety of objects with different physical properties that make them harder to detect — different shapes, sizes, materials, textures, colors, and weights.  Try dark, fuzzy stuffed animals and open-ended tubes lying on their sides, for example.
  • Second-chance game: Make the table very low,  about 1 cm.  Deduct 1 point from the score each time a robot goes over the edge of the table and touches the surface below, but do not stop the round — if it can get back on the table the round will continue. In this scenario, it might be useful to consider the color of the surface under the table.
  • Table variations: Consider using a white table with a black edge. Or, consider a square table and the challenges presented by placing objects in the corners.