Battery-powered robotic mowers mow the lawn on their own, covering an area within perimeter wires that work much like an electronic dog fence. Such mowers replenish their batteries with a charger that stays plugged into an outlet. Although they're clearly an expensive niche product, a robotic mower can pay for itself, some reviews say, compared with hiring a lawn-mowing service. Robotic mowers are the safest type of lawn mower available because you don't even have to be near them. They run quietly without polluting the air. But perhaps their main appeal is as a gee-whiz gadget. Many reviewers say they enjoy watching their lawnmower robot glide around in the yard.
The prices of the most popular brand of robotic mower sold in the U.S., Friendly Robotics' Robomowers, have dropped quite substantially over the past couple of years. Prices for the Italian-made LawnBott models sold here, however, have risen. Meanwhile, Husqvarna introduced a solar hybrid model, the Solar Hybrid Automower (*Est. $3,000) at the 2009 Consumer Electronics Show (CES), but Husqvarna still sells far more of its Automowers in Europe than it does here in the U.S. And any way you cut it, lawn-mowing robots are still really expensive. Gas-powered mowers, electric mowers and manual mowers, which cost far less, are covered in our main report on lawn mowers. Riding lawn mowers are covered in our report on lawn tractors.
We found no testing-based reviews comparing multiple robotic mowers. The best reviews we did find are on retail sites Probotics.com and Bamabots.com, though the Bamabots reviews are out of date. RobotAdvice.com reviews a couple of models based on having used them, and users at Amazon.com and Epinions.com offer first-person perspectives on Friendly Robotics Robomowers. ConsumerReports.org has a blog post and an article about robotic mowers and a review of a Husqvarna model, while The New York Times has a couple of articles that discuss robotic mowers along with other types.
Robotic mowers are much safer than other lawn mowers. They are designed to back away from an obstacle when they encounter one, and the blades don't send objects flying out the way most lawn mowers do. In addition, most robotic mowers shut off their blades within a second or two when the mower is picked up or tilted.
Though robotic mowers are advertised as freeing the homeowner from the chore of mowing the lawn, they do take some time to set up properly. Except for the LawnBott 1200 Spyder (*Est. $1,400), which doesn't need any peripheral wires, robotic mowers require extensive initial setup -- laying wire around the areas to be mowed. This can take several hours or up to a full day. Reviews suggest placing the perimeter wires somewhat tentatively at first, taking some time to experiment and find optimal placement. Several reviews note that the initial kits seldom include enough wire and pegs, but that you can substitute regular 14-gauge THHN wire and use large bobby pins as inexpensive pegs.
Reviews say that all the robotic mowers on the market do a pretty good job of mowing the lawn (though as with all mowers, you'll still need to trim the edges). Because wheels can get stuck in ditches or potholes, robotic mowers perform best on lawns with relatively few obstructions and irregularities. Keep in mind that some models perform better on sloping lawns than others, so the main factors to consider in choosing a model are your lawn's size and its maximum slope -- as well as how much you're willing to pay for extra convenience. It's important to note that the maximum lawn area specified for each robotic lawn mower is the total area it can maintain all season, not just the area it can cut in one session or day.
Another consideration is your type of grass and how short you can cut it without exposing it to heat damage from the sun. The maximum cutting height varies among robotic mower models from as high as 3.25 inches for the Friendly Robotics Robomower RL850 (*Est. $1,600) and RL1000 (*Est. $2,100) -- fine for most grass -- to as low as 2.36 inches for the Husqvarna Automower series -- suitable only for fine grass in cool, moist areas. Sound level can also be an important factor. LawnBott's robotic mowers are quietest; reviews say they won't bother neighbors even if they're mowing in the evening or at night. Friendly Robotics Robomowers are still not nearly as loud as a gas mower. But if noise level is a specific concern, reviews say, they're not your best choice.