Day 4 (14.08.08)

Wednesday, August 13th, 2008

Can Robots Mindstorm? - Day 4


Today we were working on the competition assignments. Our robot ( on the picture below) should be able to complete the following tasks:

• Find and measure distance to the box
• Open door and go into the garage
• The pushbox obstacle (push the box and drive through the gates)
• The golf course (Detect whether a ball is red or blue, then push red ones to one ditection and the blue ones to the opposite).
• The odometry test (drive the square-shaped track first clockwise, then counter-clockwise, while measuring the driven distances and detect the difference between them)

We tried very hard to do the tasks but we had several problems to solve. So, let´s keep our fingers crossed that our little robot will do fine at the competition tomorrow. =)

Here are the descriptions of how we solved the tasks:


TASK I.: Find and measure distance to the box


The robot starts going straight ahead, passes the black line, then turns 90 degrees to the right. Then it contunues going straight on until the ultrasonic sensor (mounted on the right side of the robot) detects the box. So the robot stops when the sensor is parallel with the box. The distance is shown on the display.

Problems:

• Since the sensor is not mounted above the wheels (but the distance is being measured by detecting rotations of wheels), we had to adjust the displayed distance.
  
• At first we tried to make the robot to follow the black line. This turned out to be very difficult because the light sensor was not accurate and reliable enough. Also the measured distance was not accurate.

TASK II.: Open the door and go into the garage.



Using the ultrasonic sensor and given distances we programmed the vehicle to move around the door. Then it pushes the door open, goes inside and stops.

Problems:

• The vehicle does not always turn as it should.
  
• The bumper sometimes missed the door because it was to small, so we had to rebuild it.

TASK III.: The pushbox obstacle

Our solution was to make an aggressive attack =) It simply touches the box and moves past it through the gates. If it touches the box then the movement is quite simple and effective.



No problems here =)


TASK IV.: The golf course



We attached arms and a light sensor to the robot. We had to do the task with blue and red balls, which was not very useful. The light sensor we used detects colors in greyscale, and there is very little difference between blue and red. If the sensor is pre-calibrated, it would not be able to recognize the correct color if the ambient light changes.
Therefore our robot initializes the values for blue and red ball every time before the program starts. Then it moves ahead. When the ultrasonic sensor detects a ball, it slows down. Then it stops, grabs the ball with arms, reads the value with light sensor and pushes the ball to the appropriate direction, depending on the ball`s color. Then it moves back and continues until it finds the next ball.

Problems:

• Small intensity difference between the used colours
  
• Sometimes the vehicle does not turn around in exact angels.
• Ball can bounce away if it is not caught accurately.

TASK V.: The odometry test



We calculated number of rotations of the motor needed for the given distance on each side of the square. Then we made the vehicle move around the cylinders. After one round it turns and goes counterclockwise. At the end it shows the length.

Problems:

• Vehicle does not always turn accurately, but turns for a larger or smaller angel.
  
• The latter problem was partly caused by low batteries. We replaced them, but the vehicle still does not always go the way it should.