How on Earth do Robot Mowers Work?

You wouldn’t necessarily expect the field of lawnmower design to be a place where major technological strides are being made. You’d assume that robotics would be focusing on driverless cars, military drones or household servants before moving into gardening – but you’d be wrong.

Autonomous and semiautonomous robotic lawnmowers have been in the market for more than two decades. The first fully solar-powered robotic mower (the Husqvarna Automower) became available in 1995, and the second generation versions of these machines from 2004 were able to cut a wide area by following a boundary or guide wire, and even locate their charging stations by radio transponders and automatically return to charge when they were done.

A modern Husqvarna Automower.
A modern Husqvarna Automower.


Husqvarna remains at the forefront of the metal mower revolution, although other companies have joined them. Lawn mowing giants like Honda, Bosch and Flymo have all stepped up to the plate and built a surprisingly large cottage industry.

A robot lawnmower’s number one advantage is convenience. They’re resistant to the elements, many are able to self-recharge, and they’re designed to get your garden tasks done quickly and efficiently. All modern electric lawnmowers are battery powered and run on electric motors, so they aren’t too loud or disruptive, and they’re getting quite good at dealing with tall grass or obstacles, and oddly shaped lawns. Innovations like pivoting blades that bounce rather than cut when the mower runs over a solid object, terrain mapping to generate increased power as the mower climbs steep slopes and more rugged designs to better cope with long grass. They can also cover surprisingly large areas – most of the best designs are rated to autonomously cover as much as 2,200m-3,000m. Some can cut as much as 6000m.

Robot mowers cut little and often, depending on their settings cutting 2-3mm per pass. This is the most gentle way to cut grass, reducing moss and fertilising the lawn with the short, unobtrusive clippings left behind.


How do they work?

Autonomous mowers use a simple mapping system. The user sets out a boundary wire laid into the edge of the area they want cut, which can also be extended to cover obstacles in the middle of the lawn. When the robot detects that it’s heading for the wire it changes course in a random direction to avoid it, also ensuring that it doesn’t leave unsightly track marks in the lawn through repeated crossings.

More advanced versions have 360-degree laser or radar sensors to spot obstacles in their path or incoming hazards. While almost no robot mower design is big enough to harm a person or animal they run into (bar a possible mild bruise as the confused machine bumps gently against your ankles) this system (plus integrated automatic shutdown and alarm feature if the mower hits something) makes these machines safer. Even cheaper designs have a collision sensor in their front bumper that turns them around if they hit something.

Robot mowers leave you more time to enjoy the sunshine.


Random mow systems

Most automowers have a random-mow system. They’ll drive in a straight line until they hit something, then turn around and drive off in a different direction, eventually covering the entire lawn before returning to their charging station when their batteries run dry. Robot mowers will mow continuously to get the lawn down to a healthy length, so they don’t usually mow the entire lawn in one sitting.

Some models have more planned systems, incorporating the random-walk systems into a more planned grid-mow pattern that leaves your lawn neatly lined while still allowing the mower to navigate all the obstacles and reach all the corners of the mowable area. Some even come with GPS systems that can be used to set specific paths and patterns. Husqvarna’s automower comes with an app that lets you monitor the mower and schedule cutting times, while most others have on-board control panels at the very least.

Modern mowers are also protected from theft with PIN codes and alarm systems that activate if the mower is interfered with without the PIN. More advanced models (Husqvarna in particular, although other brands have the feature too) even include a geo-fence. If taken outside a specific GPS area, the alarms will sound continuously, the machine will lock itself down and the mower will send tracking data back to the app, allowing you to locate it.

Most robot lawnmowers are designed for domestic use, but the technology is advancing and larger models are slowly getting there, offering 24-hour cutting over huge areas in all conditions. Some people won’t ever want to give up the simple pleasure of mowing the lawn, and there will always been a market for human-operated machines, but for those looking for something more convenient, robot lawnmowers are now competitive enough that while expensive, in terms of savings in labour, fuel costs and quality of cut they’re on a par with a regular petrol lawnmower, suitable for the same medium-sized gardens.

Summer’s almost here, along with the busiest time for mowing the lawn. Why not make life easier and have a robot do it for you? Lawnmowers Direct has a wide selection of robot lawnmowers