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Step 6Code Overview
Obstacle avoidance:
For obstacle avoidance the eyeRobot uses a method where objects near the robot exert a virtual force on the robot moving it away from the object. In other words, objects push the robot away from themselves. In my implementation, the virtual force exerted by an object is inversely proportional to distance squared, so the strength of the push increases as the object gets closer and creates a nonlinear response curve:
PushForce = ResponseMagnitudeConstant/Distance2
The pushes coming from each sensor are added together; sensors on the left side push right, and vice versa, to get a vector for the robot's travel. Wheel speeds are then changed so the robot turns toward this vector. To ensure that objects dead in front of the robot do not exhibit a "no response" (because the forces on both sides balance), objects to the dead front push the robot to the more open side. When the robot has passed the object it then uses the Roomba's encoders to correct for the change and get back onto the original vector.
Wall Following:
The principle of wall following is to maintain a desired distance and parallel angle to a wall. Issues arise when the robot is turned relative to the wall because the single sensor yields useless range readings. Range readings are effected as much by the robots angle to the wall as by the actual distance to the wall. In order to determine angle and thus eliminate this variable, the robot must have two points of reference that can be compared to get the robots angle. Because the eyeRobot only has one side facing IR rangefinder, in order to achieve these two points it must compare the distance from the rangefinder over time as the robot moves. It then determines its angle from the difference between the two readings as the robot moves along the wall. It then uses this information to correct for improper positioning. The robot goes into wall following mode whenever it has a wall alongside it for a certain amount of time and exits it whenever there is an obstacle in its path, which pushes it off its course, or if the user uses the twist handle to bring the robot away from the wall.
For obstacle avoidance the eyeRobot uses a method where objects near the robot exert a virtual force on the robot moving it away from the object. In other words, objects push the robot away from themselves. In my implementation, the virtual force exerted by an object is inversely proportional to distance squared, so the strength of the push increases as the object gets closer and creates a nonlinear response curve:
PushForce = ResponseMagnitudeConstant/Distance2
The pushes coming from each sensor are added together; sensors on the left side push right, and vice versa, to get a vector for the robot's travel. Wheel speeds are then changed so the robot turns toward this vector. To ensure that objects dead in front of the robot do not exhibit a "no response" (because the forces on both sides balance), objects to the dead front push the robot to the more open side. When the robot has passed the object it then uses the Roomba's encoders to correct for the change and get back onto the original vector.
Wall Following:
The principle of wall following is to maintain a desired distance and parallel angle to a wall. Issues arise when the robot is turned relative to the wall because the single sensor yields useless range readings. Range readings are effected as much by the robots angle to the wall as by the actual distance to the wall. In order to determine angle and thus eliminate this variable, the robot must have two points of reference that can be compared to get the robots angle. Because the eyeRobot only has one side facing IR rangefinder, in order to achieve these two points it must compare the distance from the rangefinder over time as the robot moves. It then determines its angle from the difference between the two readings as the robot moves along the wall. It then uses this information to correct for improper positioning. The robot goes into wall following mode whenever it has a wall alongside it for a certain amount of time and exits it whenever there is an obstacle in its path, which pushes it off its course, or if the user uses the twist handle to bring the robot away from the wall.
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