Robot Mower for Beginners

Robot Mowers  · 

What a robot mower actually cuts

A robot mower is a mulching mower that runs often instead of a mower that removes grass. It takes a few millimetres off the top of the sward several times a week and drops the clippings back into the turf, where they break down and return nutrients. Because each cut is short, the clippings are small enough to disappear into the canopy rather than forming clumps on the surface. The cutting deck carries a spinning disc fitted with small pivoting razor blades; those blades are wear items that get replaced rather than sharpened.

What it does not do is the rest of the lawn calendar. There is no grass box to empty, but there is also no scarifying to pull out thatch, no aerating, no top dressing, no rolling and no weed control. A robot mows turf; it does not renovate it. It also cannot cut the strip that the boundary wire holds it away from a wall, fence or bed, so a string trimmer stays in the shed. Long wet grass, tall weeds, fallen leaves and pruned branches are beyond it, and a badly overgrown lawn usually needs one conventional cut before the robot can take over.

Boundary wire, RTK and camera navigation

The cheapest and most common navigation scheme is a boundary wire: a single insulated loop run around the lawn carrying a low-voltage signal. The mower senses that field and treats the loop as a wall, slowing and turning away when it reaches it. A guide wire branching off the loop lets the machine leave the dock in a chosen direction and return straight home instead of hunting along the perimeter.

RTK machines replace the wire with satellite positioning. A base station fixed somewhere on the property acts as a reference point; it and the mower both track satellite signals, and the base broadcasts correction data over a radio link or the mobile network, which resolves the mower’s position to within a few centimetres. The boundary becomes a shape drawn in the app. That works under an open sky and badly under a dense tree canopy or between tall buildings, so the base station needs a clear horizon and a stable mounting.

Camera and sensor machines build a visual map from onboard cameras plus wheel odometry, recognising edges, landmarks and texture to stay inside the lawn. No wire and no base station, but the machine needs contrast and a recognisable boundary; a lawn that opens straight onto a gravel drive or a bare soil bed is the awkward case, and some sites need physical markers or an app-drawn keep-out zone.

Coverage figures versus the lawn you have

A coverage rating assumes an open, roughly rectangular lawn that the machine can reach continuously. Real lawns are not that. Obstacles make the mower slow down and detour, narrow passages force it to crawl through a gap, and a separate front garden may need either a second zone with its own guide wire or a human carrying the machine there. Slopes eat traction and time, and a wet lawn can stop work altogether.

Charging also shapes the day. The mower cuts for a stretch, returns to the dock, recharges through its contacts and resumes, so the useful coverage is the working time left after obstacle handling and dock trips. On a lawn that sits at the top of a machine’s rating, the mower may simply never finish the circuit before the grass grows again. Buying one size up, or mowing in zones on alternate days, is the usual fix.

Obstacles, islands and keep-out areas

Anything the mower should not cut through is handled either by an island or by exclusion. An island is made by running the boundary wire around a tree, a flower bed or a pond and bringing it back alongside the outgoing run; the machine reads the enclosed patch as outside the lawn and circles it. The legs of that loop need to be kept apart, because two wires running side by side cancel each other’s signal and leave a gap the mower can drive through.

Loose objects are a different problem. Toys, hoses, footballs, garden furniture legs and low shrubs get found by the bumper, lift sensor or camera only after contact, so the first season involves picking the lawn up before each run. Ponds, steep banks, the road side of a hedge and any drop to a driveway need to be excluded by the loop layout or by a keep-out zone, not left to the machine’s judgement.

Power at the dock, cutting height and season length

The dock needs level, firm ground and mains power within reach of its low-voltage adapter. The adapter should sit indoors or in a weatherproof enclosure on an outlet protected by a residual-current device, and the dock itself must be positioned so the mower can approach squarely and land on the charging contacts every time. A dock on soft ground sinks and tilts; a dock in a hollow fills with water.

Cutting height is set at the deck, usually across a range of a couple of centimetres. Start high and come down gradually: taking too much off at once scalps the crowns, exposes soil, and invites moss and weeds into the gaps. Mowing frequency should follow growth rate rather than the calendar. A spring flush means more runs, a dry summer means the machine barely needs to leave the dock, and the first hard frost ends the season for cool-season grass.

Edges, pets, children and theft

A robot cannot reach the last few centimetres against a wall, fence or flower bed, because the wire offset that keeps it from scraping also keeps it from cutting. That perimeter strip is trimmer work, and the alternative is to set the offset tighter and accept more bumping and scuffing on the mower’s shell.

Pets and children both need a rule rather than a promise. Dog waste wrapped around a spinning blade gets smeared through the deck and the wheels, so pick it up before a scheduled run. Hedgehogs, frogs and ground-nesting birds shelter in long grass and are badly served by a machine mowing at night, so run it in daylight and check the schedule when the grass grows long. Pivoting razor blades are sharp even when the disc has stopped, so a child should never be sent to retrieve a stalled mower; the PIN lock and a raised start command exist for that reason.

Robot mowers are light, portable and recognisable, which makes them a target. The dock and the wire advertise the machine’s routine, so an unpredictable start time helps. Units with a GPS tracker, an alarm or a PIN-protected start are harder to resell, and the practical step after purchase is to record the serial number and check whether an all-risk or outdoor-equipment clause in the household policy actually covers a machine left in the yard.

FAQ

Do I still need a normal mower and a trimmer after buying a robot mower?

Keep a string trimmer for the perimeter strip the wire holds the robot away from, and keep access to a conventional mower for the first cut of the season or after a long absence. A robot cannot recover an overgrown lawn, clear leaves or handle long wet grass.

Is a boundary wire still necessary, or is satellite navigation enough?

RTK and camera machines can run without wire, and they are the right answer where the lawn is open to the sky and the boundary is well defined. Under heavy tree cover, between buildings, or where the grass runs straight into gravel, a boundary wire remains the more predictable option.

Will a robot mower cope with a sloped lawn?

It copes with a gentle slope and struggles on a steep one, especially when the grass is wet and traction drops. Check the machine’s rated slope against your worst section rather than your average, and route the wire to exclude banks that the mower would slide down.

Is a robot mower safe around dogs, cats and small wildlife?

The blades stop when the machine is lifted or tilted, but they are sharp whenever the disc is turning, and a resting machine can still cut a curious nose. Schedule mowing for daylight, clear waste and toys first, and give pets a few days to get used to the machine before trusting it unsupervised.

Does household insurance cover a robot mower that is stolen from the garden?

It depends on the policy and on how the machine was secured. Outdoor equipment is sometimes excluded or sub-limited, and a machine on an open lawn may be treated differently from one in a locked shed. Record the serial number, keep the receipt, and confirm the wording before assuming the mower is covered.