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How Do Robot Mowers Work?

How Do Robot Mowers Work?

How Do Robot Mowers Work

How Do Robot Mowers Work?


You can think of a robot lawn mower like a pet you’ve never had before.

Simply put, the way a robot lawn mower works is it quietly runs around within the wired perimeter on its own (wirelessly), awkwardly pumps into things from time to time, and cuts grass for you along the way. Kind of like a real pet, so cute. It even has its own docking station where it goes to recharge on its own. As is obvious: instead of organic food, this newcomer consumes electric energy at 15 kWh on average per month (that’s almost nothing); some models a little more, some a lot less.

Now granted, there are more nuances to these hard working little gardeners.

How Robot Mowers Operate

In order to have an understanding of what robot lawn mowers can and cannot do, it’d be easier to first understand how a simple robot mower operates.

It’s a fairly simple machine on wheels designed to cut grass autonomously. In order to do just that, it needs 1) a navigation system, 2) a charging system, and 3) a cutting system. Additionally, there can be more sophisticated systems for certain other purposes, such as anti-theft or remote control system, and more, some of which almost all the latest models have by default. But I’d like to keep things simple for now.


1) Navigation of a Robot Mower

They generally go about it relatively randomly. Advanced models have a better mapping system. However, a random pattern doesn’t form any visible tracks on the grass.

When talking about the more simple robot lawn mowers, a perimeter wire is used almost like a fence for a puppy to not piss off in excitement the moment you leave the gate open. The wire is either simply laid on the ground or dug a few centimeters into the soil.

Simple in design and easily installed on your own, it’s a harmless electrified boundary wire usually connected to the robot mower charging station and making a full circle around the lawn. The robot mower can detect it, and whenever the mower gets low on battery, it follows the wire back to the recharging station. The wire also acts as an invisible walled off area for the robot to work in. And rest assured, it will happily do just that, and maybe even challenge the biggest plant you have there by bumping into it. You surround the plants you don’t want picking a fight with the mower using the wire.


How It Deals With Obstacles

However, let’s say it does run into the elders of the garden (a tree), what then?

From my years of research and observation, vast majority of robot lawn mowers are humble creatures, so usually what happens is they first bump into it, stop, at the same time turn off their blades, recalculate, turn around and begin mowing in a different direction. When they reach the boundary wire, they’ll simply change direction again. And when they get stuck and can’t get out, they’ll give up entirely and self destruct. The latter was a joke of course. They’ll start crying instead. That too was trying to be a joke, though this one had some truth in it.

However, if it’s a smaller obstacle, most robot mowers will attempt to drive over it. That means smaller plants or flowerbeds and the like without a perimeter wire surrounding them are in trouble. The solution I’ve come up with without using a perimeter wire is I’ve surrounded them with bigger round stones that block the robot mower from just driving into the area.

While some later models might not need a wire at all and can avoid obstacles entirely, the vast majority of robot lawn mowers need the wire and will run wild without it.


2) Charging System of a Robot Mower

Every robot lawn mower runs on a rechargeable battery pack that they recharge at a docking station.

The whole cycle of mowing and recharging is automated thanks to the navigation system. When the battery gets low, they automatically return to the recharging station to fill up. Mowers that rely on a perimeter wire simply run into the wire and follow it back to the docking station. All you have to do is make sure the wire-path is clear and the docking station itself on even ground for the mower to be able to properly dock.


About the Rechargeable Battery Pack

A little more about them battery packs. Not all of them are the same

Newer iterations of robot lawn mowers use lithium ion batteries. These batteries can last anywhere from 30 minutes for an entry-level cheaper model designed for small areas to up to 4 or more hours for a high-end robot mower designed for large areas before requiring a recharge. The batteries themselves can be replaced fairly easily, cost upwards of $100 and either last 2 to 3 years or 300 to 500 charging cycles. I’ve never had to change it in a couple of years myself though…

There are of course other rechargeable batteries in use even today, but lithium ion comes with several advantages in comparison. In short: lithium-ion batteries can be smaller or lighter, have a higher voltage (charges faster) and hold a charge much longer than other types of batteries (doesn’t discharge nearly as fast when not in use, and that’s a good thing because…). The only downside being its potential overall lifespan that’s not as long (2 to 3 years compared to say 6 to 8 years, but then again…).


3) Cutting System of a Robot Lawn Mower

Down there, it’s a little different from the manual push mowers or the like. Robot mower cutting blades are smaller, lighter and more energy efficient.

Instead of trying to do short work of the battlefield, roaring in pure evil and tossing its overgrown victims far and wide into the air or into a container as prisoners, robot mowers they quietly take their time slicing the grass blades more frequently leaving behind only very short clippings of grass that act as a natural fertilizer for your lawn. It’s pretty convenient and healthy for the lawn.


About the Blades

Robot mowers typically have 2 types of cutting systems: 1) solid mini blade or 2) a rotating disc with razor-like blades attached to it.

Solid cutting blade is slightly less energy efficient and makes slightly more noise compared to the rotating disc, the first is more efficient at cutting grass however.

Both of those blade types can be replaced, just like with the battery. But to tell you the truth, when my robot mower started alerting me I should change them out, I did nothing, and it still, half a year later, cuts grass just fine. It’s something to do with balance issue when it’s sharp in one location and not sharp in another location. Though I suspect some models are just a little rigged for people to spend money on their products more frequently. Almost like them printers. Except with robot mowers you can simply press “ignore” for those alerts, doesn’t just refuse to work like a printer…


Additional Nuances On How Robot Mowers Work

With the fundamentals covered, you now probably have a picture of what robot mowers can or cannot do. However, you might still have a couple more concerns on how they work.


Robot Mower Control Panel Settings

This is where you can essentially control the robot mower.

Almost every robot lawn mower has a keypad that lets you configure settings as per your preferences. The keypad lets you configure security settings, mowing schedule, cutting height, etc. The keypad is under protective sheet of plastic you can lift up. In order to make the mower STOP instantly, there’s typically a big red button on top of the robot mower separate from the keypad.


How Long Does It Take For It To Mow The Lawn?

To be fully honest, I find it hard to measure that. Every model has it written down though.

With a rectangle shaped simple patch of grassland of a typical lawn size it probably wouldn’t take all that long, maybe an hour. But if you were to add to that flowerbeds and other obstacles, for the robot mower to get to every inch of the area it would take more time. It might almost never reach to some extremely weird labyrinthic places.

But I don’t think it matters all that much. From my own experience, by the time I come back from work, everything’s cut. And since it’s scheduled to mow every day, the lawn is basically cut all the time every time.


Does It Mow It All?

It does not.

The robot mower blades can’t reach the edges, so these you have to take care yourself. The way I do it is I bring out my trimmer once a month and make short work of the edges and weird places robot mower blades didn’t quite reach. In some circumstances, the same thing happened with the traditional push mower as well anyway.


What Happens To My Kids’ Toys Left On the Grass?

You better believe they get wrecked a little bit… But only just very little. The toys I mean.

But hey, look at the bright side, it’s a very effective teaching method.


Is It Safe?

Some models of robot mowers are safer than others, but almost all of them are fairly safe in my opinion (EU regulations and all…). But it’s not completely safe. You can read about mowing robot safety here.

Most of them have both programmed and physical safety measures. For example, when it bumps into something, it stops the blades instantly, same when it’s lifted over 20 degree angle (30 degrees for some other models). Some models have an extra layer of sheet underneath, so that when you do put your hand down there, you’ll only get half a centimeter deep cuts or so.

I’ve got a chihuahua sized mini dog of unknown breed. Sometimes it just lays there without a care in the world while the robot mower is going straight at it. The guy just doesn’t care, even if he sees it coming at him. Usually I’m the one freaking out. That makes matters worse because he’ll start looking at me all confused instead of the mower. However, he gets up at the very last moment fairly casually and nothing ever has happened. Even if it did bump into him, it would likely stop the blades before anything happens. Haven’t had any accidents for years now. Even this one field mouse is still around…


Does the Robot Mower Leave Visible Tracks?

Because robot mowers are light, weighing around 15 to 30 pounds only, they don’t generally leave any visible tracks on the grass.

However, where gentle tire tracks most likely can form is at the perimeter wire. It’s because whenever the robot mower needs to recharge, it follows the wire back to the recharging station. Once it’s followed that path more frequently, the gentle tire tracks tend to form. I’ve seen it in my own garden, but I personally don’t see a problem with that. After rain or a bigger pause they tend to disappear on their own.


How Loud Are Robot Mowers?

Robot mower noise level is around 60 decibels. Pretty damn quiet.

That’s comparable to a noise level a normal conversation produces at roughly 60 decibels. In comparison, conventional push mowers’ noise level is at around 90 decibels. Noise level of 85 decibels and beyond is considered harmful for extended period of time.

The way I’d describe the noise of a robot mower would be like a mix of those friction powered wheel-like sounds that the toy cars make when you push them, but very faint ones, mostly the low-key whooshing of the rotating blades and mainly just the nibbling sound from the slicing of grass. It’s enough to make you aware that it’s there, but it certainly isn’t annoying nor repulsive or whatnot.



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