Robot Mowers without a Perimeter Wire
No perimeter wire - is it new?
There are very few robot mowers available that do not use a perimeter wire and those that do, tend to be either for large open areas (Belrobotics RTK & Husqvarna EPOS mowers) or for small gardens with specific types of boundaries (Ambrogio L60). All this may change in 2022 when we are promised a number of new robot mowers will come to market. The rise of the robot vacuum has raised peoples expectations of what a robot lawn mower should be able to do but the inside of a house is a much more controlled environment that your garden.
Why use a perimeter wire?
A robot lawn mower needs to pinpoint its position to within a couple of cms to ensure that it gets as close to the edge of your lawn as possible but doesn’t overshoot and end up in a flowerbed, pond etc. The perimeter wire/ guide wire is used by the mower to:
- Identify the extent of where it can mow and where it can’t – a signal is sent by the base along the wire and picked up by the mower as it approaches it.
- Allow it to navigate from the base to other areas/ zones…and back again - some mowers use 'guide' wires for this.
- Once it is laid, it defines the edge of the lawn and is not affected by external forces e.g. weather, visibility, tree cover etc.
- If you change your garden, you can move the wire and you know that the border is redefined.
- You are in control...if something goes wrong, it is easy to work out if it is the perimeter wire or the mower where the problem lies
What's the problem with a perimeter wire?
There are a few potential issues with having a perimeter wire:
- Someone has to install it – this means extra time if you do it yourself, or extra cost if someone else does it.
- The perimeter wire can be damaged by animals or someone putting a spade through it - there are reinforced wire solutions available.
- If you want to change the area to be mowed, it means re-laying the wire - but it is easy to join new wire to an existing layout.
Is 2022 the year?
Since robot mowers have been around for over 20 years, the issues with perimeter wires are not as major as they may seem but wouldn’t it be nice to just put a new mower down and have it work out for itself where the grass is? A number of manufacturers have been working on this for years but 2022 may give us a first glimpse of the reality...I must emphasise 'first glimpse' as the likelihood is that robot mowers without a perimeter wire will never be able to cope with all situations and hence perimeter/ guide wires will always have their place.
If you look at the products available/ announced, there are 2 fundamentally different approaches to solving the problem:
- Technology allowing the mower to identify its exact position
- Technology allowing the mower to identify grass (or lack of it) and other obstacles
People often ask us why our robot mowers need a perimeter wire if they have GPS. The answer is simple, GPS is not accurate enough, we need position accuracy to within a couple of cms, with standard GPS, the accuracy is at best 70cms but normally a meter or two, at worst it could be impossible to get a position if you can't detect 3 satellites.
This problem is not new and although the military uses enhanced GPS, experts have been working on another solution... Real-time kinematic positioning (or RTK as it is commonly known).
Read the Wiki for the details but to put it simply, as well as the GPS signal from the satellites your mower receives, you use the an additional GPS receiver (sometimes attached to the base) which transmits correction info to the mower to allow it to have pin-point positioning.
The theory is great, and you can see it in action on large open spaces (football pitches, golf courses etc. but the question is how well it will work in a "normal" uk garden. The problem is that both receivers (i.e. mower and additional receiver) need to have power, a good satellite signal and a good connection between them. Things which can affect the satellite signal are:
- The proximity of buildings/ walls, fences etc. (as the signal can bounce off them).
- The lack of a clear line of sight of the satellite which can be obscured by trees or even affected bad weather (similar to what happens to a sky satellite signal).
Grass/ object identification
Because of the problems obtaining pin-point positioning, other manufacturers have been looking at enabling a mower to identify grass and other objects so that it cuts the grass and knows where the lawn stops. In some ways, grass/ object identification is a similar approach to that taken by a robot vacuum cleaner. Radar or cameras use mounted on the mower and the inbuilt Artificial Intelligence (AI) in the mower is used to match what the mower 'sees' against what it knows is grass and other obstacles. In theory this approach should work well as it does not rely on external sources (GPS/ beacons) but the problem is that there are so many different types of grasses that it needs to recognise. Fortunately what one mower learns can be 'taught' to other mowers. Other objects which are useful to identify are:
- Raised borders/ fences etc.
- People, animals etc.
- Dog poo - a frequent question we are asked about the current mowers!
- Intruders - some manufacturers have also put some thought into using the mowers to be a mobile security camera at night.
Positioning vs object identification vs perimeter wire
So which approach is likely to give the best results? There are pros and cons of each approach, but whatever the approach, it must cope in the real world which is not the controlled environment that you see on a lot of promotional videos (or animations as there is no product currently available). The key thing to remember is that you are buying a robot lawn mower that doesn't use a perimeter wire, they still need to get the fundamentals of a robot mower (cut quality/ reliability etc.) right first and then add the ability to not have a perimeter wire afterwards. See our article on choosing the best robot mower for you. For the time being, we will not be recommending any of the machines below until we have seen production machines working in 'real' gardens.
A summary of mowers available/ planned
Terra T7 by iRobot
iRobot are best known for their robot vacuum cleaners and so should know a thing or two about robots. Unfortunately, this robot was meant to hit the market in 2019 but we are still waiting.
This uses beacons set around the perimeter of the lawn. The beacons will have to be installed by an approved installer and may not sense smaller objects, so clear your yard of small obstacles like toys, equipment, or gardening supplies before any scheduled or on-demand mowing jobs (an extract from their manual).
Navimow by Segway
Navimow is brought to us by Segway-Ninebot, again you would think they know a thing or two about positioning…but not necessarily about robot mowers. The Segway name is best known for their self-balancing transporter but you may be disappointed to find out that Ninebot bought Segway and have stopped making the iconic transporter.
The Terra uses what they have called Exact Fusion Locating System (EFLS) which seems to be RTK plus extra sensors. We have heard some good reports about this machine although the early test versions had some issues. They do say that you need to place the base station more than 2m away from buildings or fences and the base must have wi-fi coverage.
The early marketing material stated a maximum area of 3000 sq.m.
Novabot by LF Intelligence
Novabot comes from LF Intelligence whose core team were academically trained at the University of Pennsylvania.
There has been a recent crowfunding round (see the Novabot VIP Global Launch Group facebook page) and we have been worried by some of the claims that are being made in response to questions people have raised….if it will do everything they are claiming then they will have a world-beating product, but we would recommend not buying one until you can see a production model working on a real lawn.
In response to questions, they have said that this machine has an HD panoramic camera, a millimeter radar sensor and uses RTK!
They will be offering 2 models, a 1000 sq.m & a 2000 sq.m. model with delivery promised for July 2022.
EPOS by Husqvarna
Husqvarna is one of the largest robot lawn mower manufacturers and knows lots about robot mowers. They announced EPOS (Exact Positioning Operating System) a couple of years ago and have the system working on some large open spaces.
This is an RTK solution and it is not clear if this can make the transition from commercial situations (open football pitches etc.) to people’s back gardens (with trees, buildings etc.) and at what cost – the GPS reference station costs over £1000 on top of the price of the mower.
It is difficult to get much information about TOADI but it is a strange looking machine which you would image has too high a centre of gravity but it is certainly different.
It uses an HD camera, it is 3D printed and that’s about all we know. There have been reports of people sending them back as they ended up in ponds & crossing driveways. After a couple of years, it still seems to be in the beta stage so one to look for in the future.
Despite there being little information, they have just started producing some TechTalk videos. These make very interesting watching as they seem to be very honest about the issues that they have encountered and some of those issues are likely to be encountered by other manufacturers.
GPS-RTK by Belrobotics
Twenty ZR by Ambrogio
Ambrogio have been making robot lawn mowers for over 20 years so should know a thing or two about them.
Although most of the Ambrogio range has GPS fitted, they have gone down the route of grass identification to remove the perimeter wire.
The Twenty ZR builds on the very successful Twenty range and adds Radar and AI for grass detection and for identifying other obstacles.
Coverage will be 1000 sq.m. and at a price which is not much more than the Twenty Elite, it will definitely be popular.
Give us your feedback
We intend to update the above as more details become available so if you have some first hand experience of the above, or have any other mowers which you think should be added, please get in touch.