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Blind robots on the hunt! More news at 11.

Practical Exam

Christopher Merrill - Red Cohort

Concept

In order to capture the balls for the egg hunt project, the robot will resort to the use of a brute force method. The Create, mounted with a "funnel," will drive randomly around until it finds a ball. It will then cover that ball with its arm and turn towards an angle of zero (replaced with bright light source in the real egg hunt) and lauch the ball forwards.

Procedure

A "funnel" system was created using pieces of plywood and some 2x4s, and this was mounted to the front of the robot. A distance sensor was placed in the direct sensor of this funnel, and using the cricket display the reading for a distance just barely inside of the funnel was recored (250). Luckily enough, this value was close to the value obtained when the ball was very close to the sensor as well. The robot drives around in circles of a randomly varying radius at a speed of 150mm/s. If the distance sensor ever reads 250 or more, the robot will move foward slightly and drop the arm, trapping the ball underneath. It will then wait for user input (not in the actual egg hunt, but for this demo), and it will then open the arm and accelerate rapidly to 500mm/s and suddenly stop, leaving the ball traveling forward into the "goal." Once that is finished, the user must press the advance button to cause it to begin its search again (again, not in the real egg hunt). This whole procedure in enclosed in a safety system that avoids pushing into walls and drops, and allows the user to manually stop the system if required. A timer of two minutes controls the maximum time the demo can run.

Sensors, Actuators & Usage

Distance sensor, 120X (3-40 mm)
Used to determine if there is a ball within reach.
SPST Switch
Emergency stop button that is easier to press than any of the Create's buttons.
Bumpers
Detect if it hits a wall and turn away.
Cliff Sensors
Detect if there's a cliff and avoid it.
Create Buttons
Used for user control of the system.
LEDs
Used to indicate status of system. A red power LED indicates an error condition, a green one indicates a good condition. The other lights indicate which button to press to resume the program.
Cricket Display
Shows the value of the distance sensor.
Servo Motor
Controls the robotic arm used to capture the balls.

Resources

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Page last modified on January 19, 2008, at 06:13 PM