Photograph: Simon Hill
Light Detection and Ranging (Lidar): This system, also used by self-driving cars, fires rapid laser pulses to map terrain in 3D. This enables mowers to mow under dense tree canopies or near tall buildings where GPS signals typically fail.
AI vision: Some mowers now use cameras to recognize lawn areas, boundaries and obstacles. Robot mowers with AI vision could potentially avoid stray footballs, cats, other animals, and perhaps even pet messes. But they can also be very sensitive, stopping for fallen branches, leaves, or hanging plants.
Some top mowers, like the Mamotion I’m currently testing, use a combination of the previous three technologies to accurately map and mow areas, navigate reliably to and from the charging base, and avoid unexpected obstacles. None of them are foolproof. My top picks chewed up pitted paddling pools, but if you set the sensitivity too high, they left areas untrimmed.
In addition to finding your way, many of the latest robot mowers are built to handle rough terrain. Not too rugged, but fine for a rough garden or a yard with a steep slope. Some models also come with interchangeable tires, so you can fit more grippy wheels if needed. But it’s important to check what terrain and slopes your mower can handle beforehand. 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 right to the edge of your lawn. Most of the early robot mowers I tested had a thick border of uncut grass, up to 1 foot wide. I don’t think this problem has been completely 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 behind the wheels, so when the robot mower turns it can cut straight to the edge. There are even robotic mowers with built-in trimmers and other garden tools, although I haven’t tested one yet.
While edging is getting better, I still think most robot mowers need some adjustment to reliably cut the entire lawn. I often have to edit the map or change the sensitivity to make sure they cut all the way to the edge, yet there are still areas that they miss. Plants, bushes and trees overhanging the lawn pose problems, as robotic mowers understandably err on the side of caution when it comes to potential obstacles. There is still scope for improvement here.
smart finish
Husqvarna App via Simon Hill
While the first robot mower I tested made my lawn muddy, most robot mowers now have some form of rain detection feature, so you can set them not to cut if the grass is wet. The latest models are also far better at handling mulch and turning a large section of your lawn without slipping or moving.
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), which are obtained by cutting lines in opposite directions. Some mowers can also create spirals, checkerboard and other patterns.
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