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How to buy the best robot lawnmower

We explain how robot mowers work and list the features worth looking out for.

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For those of us that find mowing a chore each season, a robot lawnmower promises to theoretically end that task and give you back hours of free time. However, there's a fair bit of set-up to get this autonomous robot up to speed, so don't believe the hype without some decent research, as these can be more expensive than even the most expensive conventional push lawnmower.

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What are robot lawnmowers?

Much smaller than a conventional lawnmower, the robot mower is a reasonably automated lawnmower that is battery operated. It consists of the main mower unit and a charging dock. There's no catcher, as a robot mower cuts the lawn fine enough to distribute the grass back into the lawn. 

They're expensive compared to most conventional lawnmowers and some can equal the cost of a ride-on mower. They're suitable for lawns up to 5000 square metres (sqm), but all require a little bit of set-up to get to their reasonably autonomous state.

How do robot lawnmowers work?

When you first get your robot lawnmower, most of them will come with the main cutting unit, a charging dock and a guard wire. The guard wire connects to the charging unit and you'll have to install it so the robot knows where its limits are and can guide itself back to the charging unit. This means you'll have the charging dock close to an outlet.

Once installed, you'll set up a schedule for the robot mower so it knows when to start cutting. There'll be limitations on the length of the grass that the mower can cut – just like battery lawnmowers used to be, robot lawnmowers only have so much oomph so you might need to get the grass down to a certain length before setting off on your robot lawnmower journey.

Once those tasks are done, and your yard is cleared of any moveable obstacles such as toys from children or pets, robot mowers can work fairly autonomously – at least until you want to replace the batteries or make sure the cutting blades are sharpened.

As you can see, your first week is going to be quite labour intensive. You'll need to: 

  • set up the guard or perimeter wire
  • set up the app and outlay of your lawn
  • monitor the mower's progress to make sure it doesn't get stuck
  • check that it reaches all parts of your lawn.

From that point on it should be fairly autonomous.

How does a robot lawnmower detect edges?

One of the first things you'll have to do when your robot lawnmower arrives is set up the guard wire using supplied pegs, although some manufacturers will allow you to (or can do it for you) hide the wire under the soil.

The perimeter or guard wire is what allows the robot lawnmower to detect the edges of your lawn – there are a few lawnmowers out there that don't need this guard wire, but they are few and far between. The guard wire is not too noticeable, so it shouldn't be an eyesore once you've installed it.

Once this is done, many robot lawnmowers can be set up through an application on your phone, or on the device itself.

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Many robot lawnmowers allow you to control them with an app on your phone.

How loud is a robot lawnmower?

Unless you're very close to the robot lawnmower, you're unlikely to be annoyed by the noise. They tend to reach around 60dB which is the equivalent of a conversation – there are some which can reach 70dB (a loud conversation) which is reflected in the scores of our robot lawnmowers test.

However, these sounds are when you're very close to the mower – equivalent to a battery mower. A standard petrol mower is much noisier and can reach up to 80dB, which is the point where earmuffs are recommended. You're unlikely to be so close to a robot lawnmower as it goes about its business so it'll come across as very quiet most of the time.

What to look for in a robot lawnmower?

Smartphone app

During our tests, we look at how easy it is to use the app that comes with some of these robot mowers – we've found they range from limited to one operating system, to versatile and simple to use. You'll find it reasonably simple to use an app, assuming it works with your smartphone, rather than fiddle with the onboard controls. 

Whether you need to use the app really depends on how autonomous the robot mower is. If it comes with sensors that detect rain, then you won't need to reschedule. No mower cuts particularly efficiently in wet grass.

Some apps will allow you to set up a map of your garden so the mower knows where to go rather than in a random fashion, and some will allow you to see whether the robot mower is currently in action.

Unfortunately it's not all roses with an app – some will only work with one type of smartphone, Apple or Android, and others might use Bluetooth rather than Wi-Fi so you'll need to be closer to the robot mower to connect with it. In some cases the app might be an additional extra on top of an already expensive robot mower.

Lawn size

We've seen robot mowers suitable for lawns of up to 5000sqm, and as small as 250sqm. The maximum we've tested was 3000sqm and our testers generally agree with those manufacturer recommendations for maximum lawn size. If you select a robot lawnmower too small for your lawn size, you're likely to run out of guard wire or the mower is going to run out of puff based on its battery size. Generally manufacturers recommend buying one that's suitable for a yard a little larger than your own.

Slopes and uneven lawns

As robot mowers are powered by batteries, and they don't have a human behind them making sure they can get up a slope or avoid a dip, it's a good idea to pay attention to the slope that these mowers claim they're able to cope with. They'll give you the slope angle in degrees but the flatter the better.

An uneven lawn means dips. While we test how easily the mowers manage these dips and strange gradients that are in every lawn, the flatter your lawn, the more likely the mower is to be able to make a full round of your lawn. If the dip is significant, you might consider filling it in, or putting a barrier around it and investing in a sensor for the robot lawnmower so it can avoid it.

Sensors

Rain sensors

No mower cuts well in the wet, and robot lawnmowers are no exception. A rain sensor can be an optional extra or come with the product by default. A rain sensor will trigger off a variety of options, depending on the brand and model. It might make the robot lawnmower skip a scheduled mow, or it might alert you and ask if you want to continue with the schedule. 

Obstacle sensors

They aren't just for rain though, as many robot mowers have sensors for anything they encounter. If you have trees, bushes or other obstacles that can't be removed before the lawnmower starts off, they'll generally avoid these elements, just as a robot vac would in the house.

Multi-zone

Want your robot lawnmower to mow both the front and back lawns? You might need a multi-zone mower, so you can program both lawn sizes and design. You'll have to carry or wheel the robot lawnmower between the two spaces, as they aren't smart enough to move themselves there – yet.

Battery life

The most expensive element of any mower will be the battery, and these are larger depending on the size of your lawn you want it to cover. All of the ones we've tested are lithium-ion. Check in with the manufacturer prior to buying to see how long they'll stock the batteries and how much they are (they can be an expensive replacement) and like all lithium-ion batteries you'll start to see slow degradation over time, which will be the robot mower returning to its base unit more frequently for recharging.

You can expect batteries for robot lawnmowers to last at least 2–5 years, depending on a number of environmental conditions such as heat and cold, how often your robot needs to cut the grass, when you're cutting and whether it's stored out of direct heat.

Are robot lawnmowers safe?

Each manufacturer will instruct you not to leave pets or children near the robot lawnmower, whether in use or not. There are plenty of built-in safety features for robot lawnmowers, but follow the guidelines regardless. Even though we haven't seen a documented case of a pet's tail getting cut or robot lawnmowers climbing up a shoe, there's no point in tempting fate.

How much do robot lawnmowers cost?

Robot mowers are generally more expensive than the average battery or petrol mower, but this is dependent on their feature set and battery size. You can expect to pay $1200 and up, stretching into tens of thousands of dollars. The most expensive robot mower we tested covers up to 3000sqm, whereas the cheapest is $1299 and only covers 250sqm, which is the average size of a small house block.