How Do Robot Lawn Mowers Work?

Mowing can be a hassle, especially if you have a massive lawn. You’ve seen those sporty little mowers happily munching away at the neighbor’s grass, cutting each blade to a specific length and stowing itself away at the end of the mow. 

Is a robot mower the right choice for your lawn? This new technology is catching on, with one 2019 market report forecasting a 15% annual growth rate in mow-bot sales. But today’s models, while smart, aren’t all smart enough to deal with big ruts, steep hills or lawns consisting of disconnected islands of grass. And according to one mowing test, they just don’t cut as well as a big-engined push mower.

Not every lawn is cut out for a robot lawn mower, says Newman Aguiar of Mowbot of the Triangle in South Carolina, but he believes the concept is certainly catching on. His company offers residential and commercial robot lawn mowing services as well as traditional lawn care service. 

“When consumers actually see one of these robots and observe the technology and quality of the cut, they begin to realize that it’s a no-brainer. Their grass always looks great. It is really changing the industry — not just for consumers who do their own mowing, but also for landscape companies.

“They can offer these services and focus their labor on other elements of landscaping, and doing the other things that sometimes they don’t have time to do,” Aguiar explains.

“They can put a robotic lawnmower on their properties and have good environmental impact while keeping their customers happy,” he adds. “Rain or shine, the robotic mower is out there working.”

How Robot Lawn Mowers Work

So what are they? How do robot lawn mowers work? 

They look and act much like your Roomba robot vacuum cleaner. But they use an “Edward Scissorhands” style of clipping grass blades instead of brushing up dog hair and lint.

They hustle around your lawn on a battery charge, quietly mowing on a predetermined schedule within a predetermined area of lawn. The smaller blades are lightweight, and most brands of robo mowers have safety features that include a reverse movement if they bump into something as well as a stop feature if the mower if lifted off the ground. 

Most are programmed with a PIN code, a theft protection measure that assures thieves get no use from them. Many also include a rain sensor that stops the mower in its random-pattern tracks if bad weather hits.

You can program a robot lawn mower from the control panel installed in the unit. Many come with apps so you can control your cordless wonder from a smartphone. 

The mowers mow in different directions instead of straight lines, preventing grass “lean.” The lighter clipping of blades prevents the lawn from going into shock from a scalping mow.

Smart Mows, Within Guide Wires

However, robot mowers need to have boundaries — remember, they are only as smart as the software installed in their little 2-foot bodies.

Robot mowers have an electric mower that runs using rechargeable batteries, similar to the Roomba vacuum. The charging station is connected to a regular power outlet on the outside of the house.

“The robot charges, and then goes out and mows, and then it comes back and charges again, and then goes out and mows again,” Aguiar says. “It is an autonomous machine that manages itself and decides when to mow, how frequently it needs to mow, whether the grass actually needs to be cut.”

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But mowing schedules and other decisions are based on you and on the program installed in the mower.

To set up a mowing pattern, most robot mowers require you to install a boundary wire that runs around the perimeter of the area you want to have mowed — much like an invisible fence for dogs. 

Robot lawn mowers vary in price, beginning around $1,000 and running up to around $4,000.

Aguiar’s company uses Husqvarna robots, shifting the way his company schedules and manages a client’s property.

“Instead of using a traditional cutting blade like a traditional mower, it actually uses three razor blades, and these razor blades just make a very clean cut so they don’t damage the plant body,” he explains.

Eco-Friendly Benefits

Aguiar believes the reduction in environmental damage is the greatest benefit to using a robot mower. The battery-operated unit uses less power for recharging, eliminates pollution from gasoline, and reduces noise pollution.

“They’re quiet. You know, when most people think about mowing they think about the lawn care companies who are out there at eight in the morning on a Saturday,” he says.

“Over 5 percent of pollution in the U.S. comes from those small engines, from lawn mowing. We don’t think about how huge that impact is,” he says. “Switching to the cleaner technology of the robotic mowers, or just electric mowing in general, can have a very significant environmental benefit.”

The robot lawn mower cuts continuously, clipping small portions of the leaf blade more often than the typical homeowner who might cut grass on the weekend.

The rotating mower blades snip the blade at a different cutting height than a manual lawn mower, and allow the tiny cuttings to fall back onto the soil as mulch, where they quickly break down and add nutrients back into the soil.

The robo mower doesn’t care whether it is raining or dark outside, or whether there is a football game to be watched. It dutifully follows the installed program and cuts the grass.

Because the robot lawn mower is programmed for continuous mowing and mulching, you can’t plan for striping or bagging of grass clippings.

Not All Lawns Fit for Robot Mowers

Not every lawn is ideal for a robot lawn mower.

“An ideal lawn would be a lawn that is contiguous,” says Aguiar. “We need to install the perimeter wire that keeps the robot on the yard and also keeps it from going into things like flower beds or around trees or areas that we want to avoid.

“That wire has to be contiguous because it connects to the charging station where the robot lives, and where it recharges,” he explains.

Many traditional lawns are blocked into front and back areas, with flower beds, driveways, and other areas that don’t allow a continuous path for a robot lawn mower.

“You don’t want to put five or 10 robots on a little property. I always actually end up saying “no” to more customers than I end up saying “yes” to, and part of the reason is that most lawns are not designed for our robotic lawn mowers,” he says.

“We often have to make adjustments, or create modifications to the property that make it ideal.”

Robot mowers may not be able to perform well in areas that have steep hills or ditches, so the homeowner or lawn care company would have to mow and trim those areas manually.

Small lawn areas with short mowing patterns are also difficult to mow with robot mowers.

The Actual Mowing Gets a Mixed Review

Consumer Reports gave robo-mowers a spin, and gave them a mixed review.

Peter Sawchuck, chief lawn mower tester for Consumer Reports, put it this way in the video below:

“First, they’re expensive. Second, they take more time than you might expect to install, monitor and maintain. It’s not a matter of ‘set it and forget it,’ but it certainly does relieve you of the burden of mowing the lawn yourself, and it does give an adequate quality of cut.”

Compared to a gas-powered Honda mower, Consumer Reports and its partners from Cornell University found the robot mowers tended to rip, rather than cut, grass blades.

“What we’re looking for is for the grass to look like it has been cut with a pair of scissors — a nice, sharp, clean edge,” said Brett Welch, a technician in Cornell’s turfgrass program.

Holding a handful of grass blades cut by a robot mower, he said, “What we see going on is a bit of tearing, there’s some fraying going on, a little bit of brown tip. When it’s cut rough, it adds to stress, it’s going to dry your grass out, it’s more susceptible to disease.”

The gas-powered mower gave a cleaner, more scissor-like cut, he said.

Another shortcoming the Consumer Reports testers found: The robots need a level lawn. If there are ruts or holes, the mowers can get stuck and just spin their wheels. 

Modifying Your Lawn for a Robot Mower

Ah, but the convenience. Homebuilders are beginning to pay attention to new and improved technology — and even altering their lawns to suit their robot lawn mowers.

Aguiar is working with a local homebuilder to design a property that is ideal for robot lawn mowing.

For instance, if grass grows up to the bottom of a fence or against the wall of a home, the robot mower will leave a strip of uncut grass because of the distance between the blade and the edge of the mowing box.

But if the homebuilder installs a surface such as brick or gravel in that area, the robot mower can ride across the surface and reach the line of grass. That eliminates the need to manually trim or edge the grassy area.

Homebuilders can also install power outlets in convenient locations for charging stations, create lawns that have a continuous path to and from the charging station, and offer fewer obstacles in a mowing pattern.

“As designers and homebuilders begin to see the value of this technology, you will start to see it getting adopted more and more over the years, and it will change how consumers look at landscaping,” Aguiar says.

“If you think about it, we can see a future where a person can have a lawn that they’re never going to have to mow, right?”

Rosie Wolf Williams

Rosie Wolf Williams

Rosie Wolf Williams has kept bees, grown vegetables and flowers for farmers markets, and never misses an opportunity to have a conversation with an interesting tree.