Does anyone know how to get the compass sensor to work during the autonomous portion of the program? Everything else works fine: the ultrasonic, the motors, servos, etc.

use the motor and sensor setup and make sure you named the compass sensor something ex: compass
then just saying SensorValue[compass] will return the compass reading
note that the compass increases in value clockwise not counter-clockwise like the unit circle
that caused quite a few problems until I figured that out....

how else should the compass heading increase if NOT clockwise?

i had just assumed it would be like a unit circle where counter-clockwise is increasing values...
just didnt want him to make the same dumb mistake as I did

you've probably been thinking of sth like this

Declare the Compass Sensor

Then use something like this:


That will have the robot turn till it faces north.

0 = North
90 = East
180 = South
270 = West

You'll only get 'absolute heading' from the compass sensor in ROBOTC. I believe a few people on the forum have written code about getting a "relative heading" from the compass sensor, so look around.

We came to the conclusion that trying to use absolute headings during the competition would be problematic, because we have no idea what orientation the field will be in relative to anything else. Therefore we wrote a function to take the current heading and some angle, and add them accounting for the wrap around that occurs with 0 and 360. It looks something like this:

This doesn't do anything with the motors it simply returns a new compass heading based on an angle that you want to turn. You can then write something to turn to a new heading, or maintain a heading, or something else that is based on compass values.

What exactly does the "+=" and the "-=" mean? We thought it was "greater than or equal to" or "less than or equal to".... and it'd be helpful if you perhaps could clarify.

The code:

x += 3;

is shorthand for this:

x = x + 3;

Likewise, x -= 3 is the same as x = x - 3;

Similarly, x++ is the same as x = x + 1 and so on.

Welcome to C.

And Java, as well!

Theo

we had a quick question about the compass sensor... does this sensor always begin facing north i.e. on power up... position 0 is automatically north??? or is it that it will go towards the magnetic north??? if the second, does that mean the courses always are pointing in a certain direction???????

it uses magnetic north so you will have to make some code that will give you a relative direction if you want to navigate using relative directions ie:left & right
hint for the code: think about what you said about it starting at 0 and how you would achieve that with math given a reading
also if you don't know what global variables are you might want to look them up if you want to use a relative heading in more than one function