Mindstorm developers usually take consideration on lifting mechanism as part of their project. Lifting is one of the ability for a robot to do certain tasks such as moving and relocating an object. This mechanism uses motor or robot arm as movement mediator in providing the ability to functioning. In this week activity, our group had decided to reinforce the movement accuracy and power by attaching gears in-between the motor and lifters. We called this robot as... CLAW-TASTROPHE.
How the Claw-tastrophe works?
Command instructed to the NXT through programming. This robot will distinguish objects colour (in this case a ball) to complete the task. First, it will move forward searching for any available objects. When a blue ball encountered, Claw-tastrophe will pick the ball with gigantic claws. Inside the claws, a light sensor was attached to ‘see’ the colour of the balls. It had been programmed that if the object is a blue ball, Claw-tastrophe will release it back by moving backward, opens the claws and throw it far away with a powerful motor speed. this will happens only if the touch sensor activated after hitting with any obstacle.
Claw-tastrophe was programmed to only picking the red ball. When a red ball picked, Claw-tastrophe will turn back in 180⁰ and set forth to put the ball into a container provided at the starting line. Then, it will continue searching until the battery exhausted.
Problems and Solutions
Several malfunctions were occurring while completing assigned tasks. We manage to solve the malfunctions abruptly through redesigning, reconstructing and reprogramming the robot.
Firstly, Claw-tastrophe often failed to grab the ball successfully and make the light sensor unable to determine the colour of the ball. The problem caused by inaccuracy of ultrasonic sensor to detect the tower that hold the ball. So, the distance between the claws and the ball is too far or too close and resulting to claws unable to grab successfully. As the solution, we reconstruct the tower to be at even level with ultrasonic sensor eye so it can detect the tower accurately. The program also rechecks for appropriate value of ultrasonic sensor to react when ‘see’ an obstacle.
Claw-trastophe colour detector often 'confuse' with the colour of the balls. It used to identify every grabbed balls as blue and perform blue-assigned task only. The value of blue and red was added inapt with actual value that the light sensor can read. We realized that it was hard to set actual value that can differentiate between blue and red since the accuracy also depends on ambient light and the distance between the stimulus with the sensor. As the solution, we tried to calibrate the light sensor by put the ball close to the sensor and took the distinctive values displayed in the Mindstorm program. The distance between the ball and the sensor also reduced that allowed no other light to interfere the reading.
The third glitch is during the movement phase. Sometimes, Claw-tastrophy cannot complete the tasks cycle, in which stopped while still not delivered the ball in a container. After an hour inspection, we found that the programming was incomplete. So, we replace the linear Mindstorm block with switch, value and data to complete the task.
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