Task: Each team of three students (one mechanical engineer, one electrical engineer, and one computer scientist) were given the task of designing and building a completely autonomous robot to collect balls from a contained playing area 3' by 3' and deposit only the metal balls to a designated 'goal' in the corner of the playing area. The balls ranged in size from ½" to 1" diameter, and could be made of any material (glass, plastic, brass, steel). Complicating the project was the restriction that the robot's maximum dimensions be 12" x 12" x 12", and that the robot had to enter the enclosed playing area on its own, which required getting over a 3" wall surrounding the playing area. Each team was provided with two motors and two servos, and had a $200 budget for all other materials.
Solution: My group built a wheeled robot with skid steering controlled
by a single PIC processor. A four-bladed paddle wheel continuously scooped balls
into the robot, where they fed into an Archimedes screw. The screw was capable
of lifting any size ball in the given diameter range. After exiting the top
of the screw, the balls rolled down to rest on the metal detector, which triggered
a servo to either store the metal balls or discard the non-metal balls by allowing
them to roll off the robot back onto the playing field. After a sweep of the
playing area, the robot drove to the goal and a second servo opened to allow
the balls to drop into the goal.
Two motor controller boards controlled the two drive motors and two smaller motors that powered the paddle-wheel ball collector in front and the Archimedes screw. The robot also had eight bump sensors mounted on the exterior to help with navigating the enclosed playing area. The robot was powered by two batteries. It entered the playing area from a static platform with a spring-loaded ramp that retracted once the robot had entered the playing area.
I did all of the detailed mechanical design, based on ideas for each subassembly that we came up with as a group. These designs included detailed CAD models using Pro/E. I machined and fabricated 95% of the robot. I helped fabricate the circuit boards and also did some of the programming for the drive motors and metal detector.
Results: Our group's robot was the only robot, of six groups, that successfully
delivered metal balls to the goal area.
Images
click on images for a larger view
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Figure 1. An overall view of the robot, with the PIC processor and electronics in the upper right corner. The aluminum disk at the top of the image is the cap for the screw. The black disk to the left is the ball-sorting servo. On the right are the drive wheels with digital encoders mounted on top of the wheels. |
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Figure 2. The front of the robot, showing the paddle wheel, bump sensors (with paper clips) and the ball storage area at the top with the black servo controlling the door to the storage area. |
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Figure 3. This image shows the bottom of the robot. The motor and gear train for the paddle wheel is on the left side, while the screw is at the bottom of the image. The large white section at the top is the scoop for the paddle wheel. |
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Figure 4. A close up of the interior of the robot. Balls can be seen feeding into the base of the screw at the center of the picture. The motor for the paddle wheel is in the lower right. |