How Do Robotic Lawn Mowers Work?

Before you buy a robotic lawn mower, it's worth knowing a bit about how they work so that you can make reasonable choices when confronted by a shop full of makes and models.

There are five general areas that are important to consider:

• wheels: these vary in compound, size and arrangement;
• control: how the mower drives around, and finds the edges;
• cutting: there are different blade types and arrangements;
• battery: all robot mowers are cordless;
• programming: how easy are they to customise?

A robot mower is supposed to be a time-saving device. A true modern convenience. However, they tend to get a bad press, usually due to poor choices leading from misunderstandings around how they work.

Wheels

The mower will only be as good as its wheels and blades.

Both depend on the type of lawn. If it is undulating, and located in a part of the world which is frequently wet, then the wheels will have a big impact on the result.

Most robot lawn mowers have two drive wheels, and then one or more balancing wheels. The most common arrangement seems to be three wheels: with the two drive wheels at the nominal 'front' of the mower.

This is great for all round mowing, but tougher terrains will need mowers with more sophisticated arrangements, bigger drive wheels, and wider treads.

For example, the Robomow RX12U is a cheap, highly capable little robotic mower. But one look at it will tell you that if you ask it to mow a golf course, it's going to struggle.

Control

With very few exceptions (mainly robotic mowers used to cut large areas, like golf courses, for example) robot grass cutters use a wire to delimit the area that they are allowed to cut.

This also helps them to cut around the perimeter (so-called edge cutting mode) in certain models.

Husqvarna mowers (including Flymo and Gardena) also have a return wire that has two functions:

• guide the robot home for charging;
• start the mower from a predefined point on the perimeter wire.

This is a handy innovation for people who have lawns that are divided into zones by way of a small entry, such as a gate, or who have fairly large or irregularly shaped lawns where the mower runs the risk of missing far flung areas.

In these cases, better control of the mowing area is gained by running a wire from the base station to a far point on the perimeter wire. The mower will then, on occasion (and the frequency can be adapted in the menu) follow the wire to the end point and start cutting from there, rather than a point nearer the base station.

Newer, and more expensive, models are starting to use apps to offer better control and management over the mower, which is a trend that is very likely to continue, as is using a combination of GPS and perimeter wire.

Localised radio beacons are another control option (think of the Roomba, but outside), but these have yet to make a dent on the market; due to expense and complaints of radio wave pollution.

Cutting

Robot mowers use various blade arrangements. It's worth remembering that a robot mower is a battery powered machine, and as such weight is at a premium.

Single blades as found on traditional mowers are heavy, take a lot of energy to spin up and stop, and can create huge vibrations that make control of an autonomous nature difficult at best, and dangerous at worst.

Manufacturers of home robot lawn mowers have opted for multi-blade (usually three) cutting, usually based on a spinning disc and freely rotating blades with two or more cutting surfaces. The blades are thin, break easily, and need replacing during the season, but deliver a great cutting result.

Larger mowers, designed for bigger spaces, use single blades for robustness (such as the John Deere range of robot mowers), and some makes (such as Robomow) have slightly more robust, powered spinning blades that cost a lot more to replace, but which may be less prone to breakage.

However, the most cost effective option at the time of writing is a three bade arrangement on a spinning disc.

Battery

It's important to pick a mower that has the right level of autonomy for the lawn it will be cutting.

Lithium ion batteries are expensive, but charge quickly and can stand repeated discharge/recharge cycles without losing capacity.

For medium to large lawns, an Li based mower is clearly the best option.

However, for smaller lawns, a different approach can be used. To go back to the current low cost end of the market, the Robomow RX12U takes about 18 hours to recharge, but on a small lawn that doesn't matter, as it will usually be able to cut the whole lawn in a single session.

Programming

However, these cheaper mowers lack finesse in the amount of programming that can be done.

The Gardena R40Li for example, has a flexible cutting schedule, but even that pales into insignificance when compared to the top of the range Worx Landroids which interface with a mobile phone and can be tweaked in a variety of ways.

However, the more options you have, the more time it will take to set up the mower, and the more expensive it will be.

My advice would be that, unless you really need the flexibility to control when, how, and using what pattern the mower should cut the grass, then an entry level mower that is pre-programmed to mow at random and gives you options that are aimed more at convenience than precision is the best bet.

To find out more, check out our free automatic robotic lawn mowers buyer's guide!

Are Robotic Lawn Mowers Any Good?

Anyone reading my review of the Robomow RL 555 in 2013 would be forgiven for asking whether, despite all the hype, are robotic lawn mowers any good at all?

What a difference 4 years makes.

Not just in the technology, but also in my own opinion of robotic vs. standard walk behind mowers.

Back in 2013, I had a few choices to make regarding which mower to buy. If this report of robot mower trends to 2020 is to be believed, the field is going to widen a bit, despite the various legal challenges brought by Husqvarna in trying to protect their technology, but back then, my choices were limited to:

• Gardena (Husqvarna / Flymo / Gardena are all the same group)
• Bosch (Indego)
• Worx (Landroid, since subject of a patent infringement case)

Regular readers will know which I chose, and will have followed the last 4 years of blade changes, wheel replacement, repairing rubber bumper supports, and repairing broken perimeter wires...

...and yet despite the various trials and tribulations, I'd willingly go through it all again.

The Lawn Has Never Looked Better!

Okay, so you'll have to take my word for it, but having a robotic lawn mower has led to a greener lawn.

Why? Because the grass, when cut, is mulched.

Mulching basically reduces the clippings to a fine mist that falls back into the lawn, between the blades of grass, and helps to nourish it. Hence: a greener lawn.

The lawn is trimmed daily, regularly, and at a constant level.

It all contributes to a better looking lawn.

Yes, I still have to trim the edges, but that's more a design choice than anything else. I could have replaced the edging with little paving stones that the mower would roll over and trim right up to the edge, but I like my wood effect edges that separate the raised flowerbed from the lawn.

Once the wood rots away, as it will, I might rethink, but until then, I'll just have to do the edges myself.

Choosing the Right Robot Grass Cutter

I think that, reading the reviews on Amazon, that the biggest issue that people have is in choosing an appropriate robotic lawn mower for their lawn and level of expertise.

For example, almost without exception, robot mowers use a perimeter wire to prevent them going outside your lawn and chopping up the flowerbeds. One of the biggest ownership bugbears seems to be installing and maintaining the perimeter wire.

However, it needn't be the case.

Just be prepared to spend a little time designing the perimeter boundary, and a little more time checking that you made all the right decisions by observing the mower in action, and then relax for the rest of the season.

• Don't dig it into the lawn; just let the wire sink in naturally.
• Don't have sharp turns at the corners; either cut them or round them, checking as you go along that the mower still reaches into the corner as required.
• And don't forget that if you have height changes, pin down the wire with a peg so that it always follows the gradient of the lawn; otherwise it might just get clipped!

Make sure you choose the right mower: if you have a complex lawn shape, pick one that is designed to cover an area just a bit bigger than the actual lawn.

At the same time, if you like lines, and have a regular, rectangular lawn, then pick a mower that cuts in stripes, like the Bosch Indego, for example. It's a bit more expensive than some of the Flymo and Landroid rivals, but it does a good job provided you have a regularly shaped lawn.

In my case, the Gardena R40Li (Flymo 1200R) was more appropriate, just because of the shape of the lawn, size of cutting area, and price.

More modern mowers also exist now, complete with WiFi connection to your mobile phone and GPS to help monitor the job that they've done. I'm not convinced that app connectivity is anything more than a gimmick, but I'll admit that there is a part of me that is attracted to the idea of controlling my mower with my phone.

However, I think that it will be a while before the tweaking that you can do with such a connection actually brings something new to the party. Meanwhile, for £600, the Flymo 1200R remains my personal recommendation.

The Cost of Ownership

Another potential bugbear is the cost of owning and running a robot mower.

Sure, you don't need to spend hours actually cutting the lawn, but that's not much of a saving if you then have to spend hours in maintenance.

Luckily, most robot mowers only need seasonal maintenance, and that's mainly about replacing blades. These vary in cost: from the cheap but slightly flimsy blades used by Bosch, Flymo and Gardena that wear down often and need replacing at least twice per season and can be broken if they so much as clip a bit of gravel, to the solid traditional style blades used by John Deere robot mowers which are expensive but durable.

In between there are all manner of spinning cutters, such as those used by Robomow and Worx in their Landoid mowers, which have multiple cutting edges and spin independently.

It's worth checking, before you buy, which type of blade is needed, and the replacement cost, as well as picking the right kind of blade for your lawn. Rougher lawns with tough grass will benefit from a more solid blade, whereas lawns that have finer grass will benefit from multi-edged blades such as Bosch, Flymo and Worx use.

The important point is that, if the ends of the grass seem to be tinted slightly brown, and a ragged cut, it's time to replace or sharpen the blade. Just like with a regular mower.

One thing people forget is that a regular, walk behind mower, also needs maintenance!

So, in the final analysis, and after 4 years of robotic mower ownership, I would say that robotic lawn mowers have come into their own in 2017, and will no doubt continue to grow in popularity.

Are robotic lawn mowers any good? Yes. But, as with all purchases, be prepared to do your research, hunt down the best deal, and compromise on features that don't bring any real benefits.

To find out if a robot mower is right for you, check out our free robot mower buyer's guide, or, for a summary of all the makes and models on the market, take a look at our robot mower brand and model guide.