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# coding=utf-8
import server
mod = server.problems.load_language('python', 'en')
id = 207
name = 'Line following'
slug = 'Line following'
description = '''\
Write the program for line following. The robot should use the color sensor to follow the black line on white background.
'''
hint = {
'mW_init':mod.hint['init'],
'connectMotorLeft':mod.hint['connectMotorLeft'],
'connectMotorRight':mod.hint['connectMotorRight'],
'moveSteeringOn':mod.hint['moveSteering']+['''<p>Use move_steering method with 'on' as the first parameter <code>robot.move_steering( 'on',... )</code>.</p>'''],
'moveSteeringOff':mod.hint['moveSteeringOff'],
'connectColorSensor':mod.hint['connectColorSensor'],
'colorSensorMeasureRLI':mod.hint['colorSensorMeasureRLI'],
'while':['''<p>Use the loop, inside which the robot would follow the line.</p>''',
'''<p>The loop should be time constrained, e.g. <code>time.time()</code>.</p>''',
'''<p><code>start = time.time()\nwhile time.time()-start < 10:</code>.</p>'''],
'moveTankOn':mod.hint['moveTankOn'],
'lrPower': mod.hint['lrPower'],
'moveTankOff': mod.hint['moveTankOff'],
'time': ['''Use time() to measure time.''',
'''<p><code>start = time.time()\nwhile time.time()-start < 10:</code></p>'''],
'if': ['''<p>Use conditional statement inside the loop...</p>''',
'''<p>If the robot sees the line, it should turn slightly to go off the line; if the robot sees the background, it should turn towards the line.</p>''']
}
plan = ['''\
<p>The program should do the following:</p>
<ol>
<li>create a mindstorms_widgets() object, which represents the robot in your code.</li>
<li>connect the driving motors.</li>
<li>connect the color sensor.</li>
<li>in a loop, the robot should read the color sensor to check whether it is on or off line.</li>
<li>if it sees black, it should turn right/left; if it sees white, it should turn left/right.</li>
<li>break the loop after specified time, 10 seconds.</li>
<li>stop the motors.</li>
</ol>
<p>Note: you may need to calibrate the color sensor before running the program on the robot.</p>
'''
]
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