Remember the side where the line was last seen, and slow down in turns.
What the message means
A fast robot leaves the line between sensor readings. With no sensor on the line it does not know which way to turn.
Fix it in this order
- Store the last direction in which the line was detected.
- When all sensors see white, turn towards that side.
- Lower the speed when the error is large.
- Check that sensor spacing fits the line width.
- Mount the sensors closer to the front wheels or the line.
- Calibrate the black and white values on the actual surface.
Why it happens
At high speed the robot reaches a sharp turn or junction before the code can react, so it overshoots and loses the line. The sensors only see the line when they are over it, so the robot needs time and distance to turn.
Lower the base speed, slow down when the outer sensors see the line, and move the sensor bar further forward or widen it so the turn is detected earlier.
If you see this, do this
| You see | Do this |
|---|---|
| Leaves the line on curves | Too fast. |
| Spins in place when it loses the line | No memory of last side. |
Related
line sensor calibration, line follower wobbles.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.