Photograph: Simon Hill
Light Detection and Ranging (Lidar): This system, also used by self-driving cars, fires out rapid laser pulses to map the terrain in 3D. It enables mowers to cut grass under thick tree canopies or near tall buildings where GPS signals usually fail.
AI Vision: Some mowers now employ cameras to recognize lawn areas, borders, and obstacles. Robot mowers with AI vision can potentially avoid stray footballs, cats, other critters, and maybe even pet mess. But they can also be too sensitive, stopping for fallen branches, leaves, or overhanging plants.
Some of the top mowers, like the Mammotion I’m currently testing, employ a combination of the last three technologies to map and cut areas accurately, navigate reliably to and from the charging base, and avoid unexpected obstacles. None of them is foolproof. My top pick chewed up a deflated paddling pool, but if you set the sensitivity too high, they leave areas uncut.
In addition to finding their way, many of the latest robot mowers are built to handle rough terrain. Not too rough, but fine for a bumpy garden or a yard with steep inclines. Some models even come with interchangeable tires, so you can throw on grippier wheels when you need them. But it’s important to check what terrain and inclines your mower can handle upfront. Four-wheel-drive or all-wheel-drive mowers are best at handling steep or uneven ground.
The Cutting Edge
Traditionally, robot mowers have been terrible at cutting all the way to the edge of your lawn. Most of the early robot mowers I tested left a thick border of uncut grass, up to 1-foot wide. I don’t think this issue is entirely solved, but some newer models have offset blades that sit closer to the edge of the machine, or they have an overhanging section that extends past the wheels, so it can cut right to the edge when the robot mower turns. There are even robot mowers with built-in trimmers and other garden tools, though I’ve yet to test one.
While edge cutting is getting better, I still find that most robot mowers need some adjustment to reliably cut the entire lawn. I often have to edit the map or tweak sensitivity to ensure they cut all the way to the edge, yet there are still areas that they seem to miss. Plants, shrubs, and trees that overhang the lawn cause issues, as robot mowers, understandably, err on the cautious side when it comes to potential obstacles. There’s still room for improvement here.
Smart Finish
Husqvarna app via Simon Hill
While the first robot mower I tested churned my lawn into a muddy mess, most robot mowers now have some form of rain detection, so you can set them not to cut if the grass is wet. The latest models are also far better at handling wet grass and turning without skidding or churning up a big chunk of your lawn.
Some robot mowers offer customization in terms of the lawn finish you want. You may find an option in the app for Wimbledon Stripes (dark and light stripes), achieved by mowing rows in opposite directions. Some mowers can even do spirals, checkerboards, and other patterns.