Robotic lawn mowers are certainly a practical help in the garden. However, we don’t have one of those geometrically perfect new-build plots, but rather an established garden with all kinds of angles, no fixed lawn edges, and areas that aren’t contiguous. Our terrace isn’t finished yet either, so the wire would have to be re-laid anyway, and using a scarifier wouldn’t be a good idea either. Laying a perimeter wire would therefore not only be very laborious - in our case it would be almost impossible. I keep hearing from many people how often a severed perimeter wire has to be found and repaired.
Unfortunately, the wire loop is still the standard technology for all robotic mowers, whether Gardena, Bosch, Worx or whatever they’re called. Only recently, a Kickstarter campaign for the “Toadi” mower attracted attention. The Toadi is supposed to navigate and find its way using object recognition alone. They’ve now raised 1.5 million euros for it, but unfortunately there are no details about the technology and somehow the whole thing seems rather unconvincing. I’ve already reported on it HERE . At 2,471 euros for Kickstarter backers, it’s not exactly cheap either.
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Robotic lawn mower with GPS navigation
The only sensible way to make a robotic mower drive precisely without a perimeter wire is GPS. However, conventional GPS reception is too imprecise for this, with deviations in the range of 5-10 meters - far too inaccurate for this task. Differential GPS provides a solution. Here, the GPS data of the moving object is compared with that of a fixed receiving unit. From the deviation of both receivers, a correction value can be calculated, which then enables an accuracy of 1 cm. This technology is known as GPS/RTK (Real Time Kinematic), but is unfortunately quite complex and therefore expensive.
The robotic mower manufacturer Husqvarna is currently advertising the Husqvarna EPOS mowing system , which uses GPS-RTK. However, the manufacturer states that the system will initially be offered for professional users (football pitches, golf courses, parks) and only from 2021. For private users, the technology is probably still a long way off, as the price for a robotic mower equipped in this way is estimated at around 10,000 euros.
So a robotic mower suitable for our garden was out of reach - or so I thought.
ArduMower: DIY sustainable robotic lawn mower with GPS-RTK
I first heard about the ArduMower project at Maker Faire 2015 in Berlin. There, a self-built robotic mower was merrily doing its rounds. Five years later, the ArduMower not only mows in lanes, but also without a perimeter wire. The guys have managed to integrate GPS/RTK into their open source robotic mower in a comparatively affordable way. This means you can use your smartphone to teach the ArduMower the boundaries of the lawn area by simply driving it around the edges once. From then on, the ArduMower can precisely mow the learned area using GPS/RTK - without any error-prone wire loop or camera functions.
The ArduMower itself consists of robust components that you can either make yourself or order from the ArduMower shop Marotronics . There you can get all components and useful accessories. The housing is made of milled PE sheet material, but a Dibond version will soon be available, which is significantly lighter while offering the same stability.
The heart and intelligence of the ArduMower is an Arduino to which common sensors and modules from the Arduino world are connected. Marotronics offers a mainboard that connects all components. You can also get this board on its own for just under 60 euros.
In principle, the ArduMower project also allows you to convert an existing (defective) robotic mower, and with a 3D-printed housing it can also look very stylish. A pure electronics set for the DIY robotic mower is available from around 440 euros.
It is powered by a 25.2 volt lithium-ion battery with 5 Ah, two powerful geared motors for the wheel drive, and a motor for the blades. You can of course also operate the ArduMower with a wire loop, but the new GPS/RTK version is what’s really interesting.
A complete ArduMower kit for wire loops including the loop installation kit currently costs 669.54 euros plus around 130 euros for the battery pack. For that, you get a robust, freely configurable and, above all, repairable robotic mower with plenty of expansion options and an open software platform. This is playing an increasingly important role for me: I no longer want to have to throw away devices because a tiny defect makes repair uneconomical or the manufacturer stops developing the software.
There are two options for the GPS/RTK version:
ArduMower with its own base or via SAPOS service
As mentioned above, the ArduMower requires a correction signal for precise GPS navigation. This can be obtained via the “SatellitenPositionierungsdienst” (satellite positioning service) of the German land survey authority SAPOS as an internet service.
Several stations have been installed for this purpose, which make their data available via web service. But here, federalism rears its head again: while the service is free in some German states, here in Bavaria they charge 10 cents per minute of use for the high-precision HEPS service or a flat rate of 250 euros per month (!!).
If you can use SAPOS HEPS free of charge in your state, this would have the advantage that you would only need one GPS/RTK receiver in the robot. At just under 390 euros , this receiver isn’t exactly cheap. The ArduMower uses the ArduSimple system with a uBlox receiver here.
A complete kit for this is offered at Marotronic for 961.83 euros . The SAPOS data is then transmitted to the robot via WiFi and compared. This of course requires WiFi coverage of the lawn area, e.g. via an outdoor access point .
I’ll have to use my own stationary GPS/RTK, which I’ll mount on the house roof. Here too, you can get a complete mower kit for 1,363.73 euros from the ArduMower shop. The connection between the stationary receiver and the ArduMower is made via XBee modules, so no WiFi is required in the garden.
My own ArduMower
The complete set for my ArduMower has been ordered and it will get a red Dibond housing with a white lid. The biggest effort will probably be populating the mainboard. I also need to provide a mount for the GPS/RTK receiver and build a robot garage with contacts for charging.
Of course, you can also go to the nearest hardware store or garden center and get a run-of-the-mill robotic lawn mower for less money, which might also look nicer. But with the ArduMower, you get a sustainable robotic mower platform that is expandable and repairable. The ArduMower also doesn’t work on the chaos principle, but mows in lanes or patterns. This is much more efficient in terms of battery capacity and blade wear than the random pattern of conventional systems.
The makers are currently considering an additional camera that can detect objects early, and the Bumper-Duino , which can detect contact with obstacles not via mechanical switches but through air pressure changes in a tube, is almost ingenious. Moreover, the IKEA effect says that we value things more when we’ve made them ourselves. I already have a few ideas of my own. Another topic will be integration into our smart home with Symcon , and soon an automatic lawn irrigation system is also planned.
More info:
<https://www.ardumower.de
Hi! I'm Markus – the Fricklr. ⚡ Electrical engineer, 🎵 musician (bass, guitar, keys) and professionally 'something with the internet' 🌐 for over 30 years – nowadays with AI too 🤖 – a 55-year-old generalist from Bavaria, Germany.
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