The Perils of a Robot Lawnmower with No Perimeter Wire

I get a lot of questions directed to me about installation of a perimeter wire and the reason why all of the major brands (Bosch, Worx, Husqvarna, Flymo, Gardena, etc.) rely on this technology. The fact of the matter is it wasn't always the case, and it's also still possible to buy robot lawnmowers that don't rely on a perimeter wire to delimit the mowing area.

But, is that a good thing?

Let's look at a few of the options available to manufactures using today's technology.

Robot Mower with Sensors

Mowers like the LawnBott Spyder, for example, don't use a perimeter wire. In fact, according to the LawnBotts web site, this is hailed as "a new beginning for robotic lawnmowers."

However, I would dispute this, as I have a friend with a sensor-based mower that pre-dates my own Husqvarna/Gardena R40Li, which he inherited from a family member who I assume had upgraded to a better version.

A quick question and answer session later revealed that while there are issues with sensor based mowers, largely my friend was well satisfied with the performance of the mower. However, there were a few basic flaws.

The first is that without a ground wire, the mower has to way to find it's way "home" for recharging. Therefore, it has to be charged indoors.

In fact, the mower has no way of knowing where it is, or where it has been; it's a dumb mechanical device, with none of the intelligence built into more modern models.

The way that they work is simple: they have sensors facing down which detect grass, and bump sensors to prevent chopping up the family pet. The lawn sensors rely on moisture detection, and the ability to tell the difference between mildly damp grass and, say, concrete or gravel.

My own feeling is that this is fine for most regularly shaped, enclosed areas, but as soon as you add a pond, or something that can become overgrown and poses a threat to the mower -- either damaging it, or allowing it to 'escape' -- I wouldn't feel personally comfortable relying on a few sensors to keep it in check.

Then there's the security aspect: one can imagine that stealing a plug-in to recharge mower that doesn't rely on a coded perimeter wire signal is a bit more of an attractive option than one which relies on a fully wired-in installation.

However, there are other options.

Robot Mower with a Virtual Perimeter Wire

These fall into two categories:

• Roomba style transmitters;
• Remote control / smartphone control plus learning.

In 2015, iRobot secured the go-ahead from the FCC to develop and deploy the same kind of technology that is used for their Roomba robot vacuum cleaners for outside use. This would allow them to create an iRobot lawnmower. Because it is guided by localised positioning using radio waves, however, it sparked anger amongst radio astronomers.

Of course, since then, their flagship technology has moved up a gear, and now uses all kinds of visual cues and smartphone interaction to "map and adapt" to the task in hand, rather than using navigation pods. Perhaps this move away from the older technology explains why we haven't seen the iRobot lawnmower as yet.

That leaves remote control or smartphone control plus learning. In fact, SmartMow has pinned their hopes on this approach, and have patented "Virtual Boundary Technology" which they explain as the ability to "Just walk SmartMow around the perimeter of your yard".

I'm actually looking forward to reviewing the SmartMow, because it appeals to me on a number of levels, including some exciting technology for connecting to it via a web portal.

The idea seems to be that the mower will learn where the perimeter is by being "shown" it, and then left to its own devices. Of course, the mower also has the regular sensors to allow it to avoid unexpected objects, but because the solution is software rather than hardware, my reservations re: ponds and robots going mad (as in the movie Short Circuit) still hold.

Robot Mower with GPS

Everything from farm machinery to those massive machines that rake the pistes in the Alps use GPS, so why not home robot mowers?

Husqvarna's Automower does just that. It even has its own app to help you fully take advantage of the set and forget nature of automatic robot lawn mowing.

(By the way, these are at the expensive end of Husqvarna's range -- the affordable models still use a perimeter wire... as do the ones with GPS!)

But here's the thing; it still uses a guide wire, presumably for security reasons.

In fact, aside from this experimental design from 2016, I was unable to find an example of a commercial automatic lawn mower that relied 100% on GPS for its perimeter detection and mowing capability.

So, all in all, it seems as if the good old perimeter wire is here to stay: sometimes lo-tech is really the best tech! If you're still wavering, read our Perimeter Wire Tips & Tricks Post; I'm pretty sure you'll agree that it's still the easiest, safest and most reliable method of keeping your robotic mower in check.

Robot Lawn Mower Perimeter Wire Tips & Tricks

Based on the last few years of robotic lawn mower ownership, I have a number of trips, tricks and tools for setting up and maintaining my robot lawn mower perimeter wire, as well as some recommended products.

A key point to remember is that while some of these parts are compatible (pegs and connectors, for example) many of them are not. At the same time, for some of the more basic installation and maintenance tasks (extending the perimeter wire, for example) regular off-the-shelf third party components can be used.

Robot Lawn Mower Perimeter Wire Installation

The first tip is to be prepared to move the wire around after it has been installed. For this reason, I recommend laying the wire on top of the grass, rather than digging it in.

Figure 1 : Poor Return Wire Installation

My first attempt at laying the perimeter wire wasn't exactly a triumph (see Figure 1).

Our lawn mower is the excellent Husqvarna 105 / Flymo 1200 / Gardena R40Li, and I followed the instructions to the letter.

What I forgot, however, is that something the size of a robot mower doesn't easily pass through a gap in a fence.

In addition, the design of the mower actually gives you a way out -- in the form of the return wire (the blue line in Figure 1). How it works is this: the mower leaves the charging point (on the right) and mows the lawn at random.

When it runs out of power, it will look for the return wire, and follow it back to the charging station.

The trouble is, when installed as above, the mower will (a) rarely make it into the top-left, and (b) once it's there, it will run out of power looking for the return wire, which it almost never finds.

There are a few solutions to this. The simplest is to to carry the mower to the top-left, and then remembering to get if back again once it runs out of juice.

However, the saving grace comes from the mower's design.

Figure 2 : Better Return Wire Installation

Reading through the instructions it transpires that there is a way to get the robot to follow the return wire at the start of a mowing session.

This led to the solution in Figure 2. The black line shows the new location of the return wire, designed to help the mower find its way home.

At the same time, once set up correctly, the mower will, occasionally, start from the end of the return wire.

One last note: since I had already installed the blue wire, I didn't want to uninstall it, so I added a box that enables me to switch between the two. I'm cautious like that.

To achieve this, I used some kit from the following section.

Lawn Mower Perimeter Wire Maintenance

Although tough, perimeter wires can be broken. Especially if, like me, you've scrimped a bit and bought some lesser grade wire to extend the length of that which has been provided.

Figure 3: These are not the connectors you are looking for...

Here's a first hint: buy the wire that is recommended by the manufacturer. It's just better.

But, it's not indestructible, and so it helps to have a few bits of kit that can help you when the worst happens and someone cuts through it with a spade, or a rodent chews through it.

Or, more likely, one of the little terminal blocks that you used to connect two bits together fails.

These are not good connectors. They are not waterproof, and, over time, will fail you. In my case, it took about 18 months to 2 years before the first one failed. I've now replaced all of them.

The replacement connectors are hugely expensive. Luckily, I've found a place where you can get a selection of waterproof wire connectors for use on the perimeter wire, all very inexpensive.

My absolute favourite, though, is the damp-proof wire splice connector available through Amazon, pictured here in Figure 4.

Figure 4 : Better Wire Connectors

Firstly, they're not 100% waterproof, but I've found that this doesn't really affect them too much. Certainly not as much as a simple terminal connector.

They're also reasonably priced, and because you have to crimp them, they do hold better than some of the other solutions.

Finally, they're a 2-way and not a 3-way connector, so are less bulky when you have to partially bury them. The 3M ones that came with the mower tend to stick up and risk being sliced on the lowest blade setting.

With the connectors sorted out, there's just one item left: what happens when the lights go red?

Perimeter Wire Emergency Kit

The most common thing that happens is that one of the plugs at the back of the charging station pops out, breaks, fails, or otherwise needs replacing.

Figure 5 : Spade Connectors

Sometimes, it's enough just to push it back in. However, on occasion, they actually need to be replaced. Luckily, they're just spade connectors, and easily found on Amazon, for very little money.

In Figure 5, there's an example. For connecting to the Husqvarna / Flymo / Gardena base station, you'll only need the bit that crimps to the wire (perimeter / guide wire) and the other end 'plugs into' the base station.

However, these connectors also form part of my Perimeter Wire Emergency Kit, and can be used with any of the popular makes.

It's worth mentioning that any robot lawn mower with a perimeter wire needs a way for you to locate a break in the wire.

Typically, this requires connecting a 'flying wire' to the base unit (charging station) and then connecting it at various points around the perimeter wire to see where the break occurs.

But this is very troublesome if you need to go around breaking the wire and connecting a 3-way block to the perimeter wire before plugging in the flying wire. 

Figure 6 : Self Stripping Connector

Much easier is to use the self stripping connector type, as shown in Figure 6.

All you need to do with these is place them around the perimeter wire (with flying wire connected) and gently press the cover closed just enough to make the connection, but not enough to seal the connector.

If you press too far, don't panic, just leave it where it is.

These connectors are so cheap that you can afford to leave them in place -- and if you mark where they are, the next time you need to investigate a break, you just need to march up with your spade connector on the end of the flying lead, and plug it in!

One last tip: the flying wire need not be the best quality, but is must be long enough to run to the most distant point on your perimeter cable, as measured from the charging station.

So, those are the current robot lawn mower perimeter wire tips and tricks, from a few years of robotic lawn mower ownership. Feel free to add your own solutions in the comments below!