View source for Regbot calibration

=== Crossing detect ===

The crossing detect (Crossing det.) value basically based on the measured width of the tape.

If the robot is centered on the one edge, and the tape is more than 3cm wide, then the measured width is 3cm. If the crossing detect threshold is 3 (cm), then it is likely that it will detect it as a crossing line. If the threshold is 5, then a crossing threshold should not be detected.

There is 2 modifiers to this scheme.

* 1. If the width increases with movement, then the increase over the last 2mm of movement will be added to the sensed width. 
This means that when approaching a crossing line at an angle, then the triggering of crossing line will be faster. This feature is especially important as there otherwise would be a tendency for the robot to follow the crossing line, or turn a bit in that direction.

 Code is like this, with kd = 10 and edgePos2mm is the edge position 2mm ago: 
 vl = lsLeftSide + (lsLeftSide - edgePos2mm[0]) * kd;
 vr = lsRightSide + (lsRightSide - edgePos2mm[1]) * kd;

* 2. If the robot turns (rotates), then the effect in modifier 1 could easily trigger a crossing. To eliminate that the gyro signal around the vertical axis is used to counteract (z axis on REGBOT and x axis on ROBOBOT (on default mounting)).

 Code is like this (findCrossingLineVal is the total width before applying the threshold):
 const float kg = 0.0005;
 // on ROBOBOT z-axis is gyro x, on REGBOT it is z, so add the two
 findCrossingLineVal = vr - vl - fabsf(imuGyro[2] + imuGyro[0]) * kg;

If crossing is detected the crossing count increases up to 20, and decreases down to 0 if not.

On figure 4, the threshold is 6.5, i.e. larger than the sensor width, it will then be triggered on fast approach to a line only.
A crossing value of 4.5 is often a good value.

==== Crossing effect on line edge following ====

When the crossing line count is > 0 (i.e. at least one crossing detected), then the line follow control will be disabled (the robot will go straight).