Subject:
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Re: September 18th 2004 SMART Meeting Notes
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Newsgroups:
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lugnet.org.us.smart
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Date:
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Tue, 21 Sep 2004 06:18:32 GMT
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Viewed:
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2086 times
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Oh, for the BrickHeap Wars competition, I also provided a small snippet of
line-tracking code that teams could use if they wanted. The code isn't
guaranteed to work, and depends on the geometry of your robot, but it's a good
starting point if you're in a real hurry, like the teams were during the
competition, or if you've never written a line tracking robot before, and need a
place to start.
Here's the code:
Two-threshold Line Tracking
Sensor_1 is a light sensor, left and right motors are on A and C respectively.
The robot either starts with the light sensor on, or to the left of the line.
‘lightThreshold’ is a value close to the sensor’s reading for light, and
‘darkThreshold’ is a value close to the sensor’s reading for dark. Both motors
are off before entering the loop.
while( true ) // UNTESTED CODE!!!
{
On( OUT_A + OUT_B );
While( SENSOR_1 < darkThreshold && SENSOR_1 > lightThreshold )
;
Off( OUT_A + OUT_B );
On( OUT_A ); // Start turning right
while( SENSOR_1 > darkThreshold ) // ...keep turning while on the line
;
Off( OUT_A ); // ...stop turning once off the line
On( OUT_C ); // Start turning left
while( SENSOR_1 < lightThreshold ) // ...keep turning while off the line
;
Off( OUT_C ); // ...stop turning once on the line
}
Note that when calibrating your robot, the thresholds should be moved 'towards'
each other; say 10% of the distance. Some calibration code might look like this:
int darkest = SENSOR_1;
int lightest = SENSOR_1;
int curr;
while( true )
{
curr = SENSOR_1;
if( curr < lightest ) // assuming *raw* values
lightest = curr;
if( curr > darkest ) // assuming *raw* values
darkest = curr;
lightThreshold = lightest + (darkest-lightest) * 1 / 5;
darkThreshold = darkest - (darkest-lightest) * 1 / 5;
}
Hope those are useful! Don't be surprised if they'll need a bit of massaging
before they'll work for your robot. And don't forget to define your sensor
before using it. Something like:
SetSensorType (SENSOR_1, SENSOR_TYPE_LIGHT);
SetSensorMode (SENSOR_1, SENSOR_MODE_RAW);
should work.
--
David Schilling
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Message is in Reply To:
 | | September 18th 2004 SMART Meeting Notes
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| Our annual BrickHeap Wars competition this year was not as strongly attended as previous years, but the people who did attend had a ton of fun. The challenge given at the start of the meeting was to build a robot that would track a line and be able (...) (20 years ago, 21-Sep-04, to lugnet.org.us.smart)
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