A robot mower that leaves uncut patches is usually cutting with worn blades, running a coverage pattern that misses corners and narrow passages, steering around obstacles or wet spots, or simply not getting enough run time to reach the whole lawn.
The usual causes
- Worn or damaged blades. Dull, chipped, or bent blades tear rather than cut and drag through thicker growth, leaving standing grass in denser areas.
- Coverage pattern gaps. Corners, narrow strips between beds, and areas past a tight passage are common misses because the mower cannot maneuver fully into them.
- Obstacles and no-go zones. Furniture, toys, low branches, and mapped exclusion zones make the mower steer away, leaving a ring of uncut grass around each object.
- Slopes and slippery ground. On inclines or wet grass the wheels can slip, so the mower covers less ground than its pattern intends.
- Run time too short for the area. If the schedule or battery runtime does not match the lawn size, the mower charges before it finishes, and the same far corners get skipped each cycle.
- Boundary or position drift. A boundary wire placed too far inside the edge, or an RTK mower with a weak fix near tree cover, can keep the mower off the true perimeter.
Fixes to try in order
- Inspect and replace the blades. Power down the mower, turn it over, and check each blade for dullness, chips, and free movement. Replace a worn set rather than sharpening if the design uses small pivoting blades.
- Raise the cutting height, then lower gradually. If grass is tall or dense, set a higher deck first and step it down over several sessions so the mower is not forced to muscle through heavy growth in one pass.
- Increase run time or frequency. Lengthen the schedule or add sessions so the mower has time to reach every zone, especially far corners and areas behind passages.
- Clear and re-check obstacles. Remove movable items before each run and trim low branches. Review any mapped no-go zones and confirm they are not larger than intended.
- Adjust the boundary or mapping. For wire systems, reposition the perimeter wire so the mower reaches the true edge. For RTK systems, confirm a strong satellite fix and remap corners that sit under tree cover or beside buildings.
- Check the wheels and tires. Clean caked grass from the drive wheels so they grip and track the pattern accurately on slopes and damp ground.
When it is the mower, not the lawn
If the blades are sharp, the schedule is generous, and the yard is clear but patches still appear in the same places, suspect an internal fault. A worn wheel motor that slips under load, a failing tilt or position sensor that cuts a pass short, a cutting motor that bogs down in normal grass, or a firmware regression that changed the coverage pattern after an update can each leave repeatable missed spots. Note whether the skips started right after a firmware update, since that points to software. Track model-specific reports and update notes on the Tracker, and see our overview of robot mower autonomy.