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DIY English OpenMower Technology

OpenMower – The DIY Smart Robot Mower for Everyone

Why Bother Building a Robotic Mower?

If you’re in the market for a robotic lawn mower, you might have noticed that most models operate using the same principle: A perimeter wire is laid out around your yard and the robot simply follows this simple algorithm:

  1. drive straight until perimeter wire is detected.
  2. back off a little, rotate for some random time; goto 1.
  3. if battery is low, follow the wire until the base station is found.

This approach works fine for small, uncomplicated lawns, because due to the randomness, the robot will eventually reach all parts of the lawn.

Unfortunately, the approach also has lot’s of drawbacks:

  • If the garden is split into multiple areas, the robot mower is not able to roam between these areas.
  • If the lawn area is too large, it will take a long time for the robot to randomly reach every part of the lawn.
  • The mowing pattern is not even. After manually mowing the lawn, you get a nice and even cut, whereas most robot mowers produce a random looking pattern.

Unfortunately, our property has multiple features which makes it unsuited for traditional robotic lawn mowers. Therefore I decided to build my own robotic lawn mower. Additionally, such a project is a lot of fun!

What Are the Requirements for the Robot?

After the decision to build a robotic lawn mower was made, we specified the following requirements:

  • It shall be able to autonomously mow our lawn (obviously)
  • It shall feature good safety. (i.e. turn off if lifted or stuck, emergency stop button, …)
  • It shall not require a perimeter wire
  • It shall be low cost (i.e. cheaper than a mid range off-the-shelf product)
  • It shall be open source so that other people can use the project as well
  • It shall be efficient and low-maintenance. (i.e. if I need to invest more to service the robot than I’d need to mow my lawn, the device is useless)
  • It should be nice to look at. (i.e. not ugly)
  • It should be able to avoid obstacles, but shall at least stop in front of obstacles
  • It should be able to detect rain and pause mowing until weather conditions improve

With those requirements in mind, a concept was created.

The Concept

1. Mechanics

In order to come up with a good mechanical hardware design, we researched the state of the art of robotic lawn mowers. The basic hardware design is very simple and similar between all of the products. Each robot consists of three sensored brushless motors, some buttons, some sensors in a waterproof case. Two geared motors for moving the robot and one directly driven motor for the mowing unit itself. The mowing motor has a spinning disk attached to it which itself holds the mowing blades. Most models also feature two passive wheels which are dragged around by the robot.

The commercially available models have contain the following safety features:

  • An emergency stop button
  • Wheel sensors which detect if the robot is lifted or went off a cliff
  • A simple gravity sensor which can detect if the robot is flipped

After many hours of comparing robots and looking for replacement parts (connector documentation, parts numbers etc), we realized that upgrading an off-the-shelf robot is the best solution!

The reason behind this decision is simple: For as little as 350 € you can get a basic robotic lawn mower, but you can’t even get the parts you’d need to build one yourself! Additionally, by buying an off-the-shelf product, you get a nice looking, waterproof case included which saves a lot of time for this project.

For our robot, we chose the YardForce Classic 500 robot, which at the time cost 399 €. It is a little more expensive than the cheapest options we found, but we were fairly certain that it was hackable and had enough battery life for our application.

2. Electronics

Unfortunately, in contrast to the mechanics, we cannot really reuse existing electronics in the mower. The reason for this is, that on the one hand the electronics are not powerful enough for our use case and on the other hand, the electronics are closed source. Therefore we’d need to reverse engineer it in order to use it.

At this stage of the project, we’re not 100% sure about the electronics to use in the robot, but some components are a perfect fit:

  • The Raspberry Pi 4, since it is widely used and has enough computational power. Additionally, it features up to five hardware serial interfaces, which allows us to talk to lots of peripherals.
  • A RTK GPS board for positioning. Since we won’t use a perimeter wire, the robot needs to know its position on a known map. We decided to use the Ardusimple RTK GPS baord.
  • Three Brushless Motor Controllers: In order to accurately control the three brushless motors in the mower, we use the xESC mini brushless motor controllers. This controller enables us to control the motors with FOC commutation and even provides positional and current feedback to the controller.
  • A Raspberry Pi Pico as low level controller. The Pico is perfect for this use-case, since it features a fast dual-core CPU with lots of IOs. It will handle sensor IOs etc.

Next Steps

The next steps are to create a hardware architecture, build a mainboard, put it together and then write some software for the robot. If you want to get updates to this project, you can star the GitHub project: https://github.com/ClemensElflein/OpenMower



Entrepreneur, Loves Software Engineering, Hardware Design, Robots and Open Source.

Comments (41)

  1. Norbert
    April 6, 2022

    Very interesting project.
    I will follow you.
    Me and my wife are going to move into a house this summer, and I was planning to buy a robot for a 1000m² lawn. Your project comes at just the right time for me.

  2. haze
    April 6, 2022

    hi, it is a good project
    I would like to know where you buy Mechanics with wheel, motor, battery ect…

    Thanks you

    • Clemens
      April 7, 2022

      I just bought it on Amazon. The Robot is called YardForce Classic 500.

      • Jürgen
        April 21, 2022

        Hallo Clemens,
        ich bin eben über dein YouTube Video gestolpert, und völlig begeistert.
        Ich selbst besitze seit 2 Jahren einen Worx Mähroboter, mit dem ich eigentlich ganz zufrieden bin. Er läuft zuverlässig und vor allem mäht er relativ gut in die Ecken durch sein nach außen versetztes Mähwerk. Wenn da nur nicht der Begrenzungsdraht wäre🙈, der trotz aller Vorsicht schon mal durchtrennt wird. Sollte sich jetzt deine Elektronik in den Worx integrieren lassen, wäre das wunderbar. Denkst evtl. daran deine Technik auch für andere Mähroboter integrierbar zu machen? Jedenfalls wünsch ich dir viel Erfolg für dieses Projekt. Ich werde dich beobachten.
        Schöne Grüße

        • Clemens
          April 21, 2022

          Vielen Dank für den Kommentar! In der Community wird gerade daran gearbeitet die Technik für andere Mäher zu verwenden. Worx Modelle sind auch dabei, benötigen aber mehr Anpassungen als andere Mäher. Es wird deshalb wohl noch etwas dauern, bis der Worx Mäher kompatibel ist.

        • Adem
          April 26, 2022

          Hallo Clemens,
          Erstes mal großes Lob an dich.
          Und zum weiteren hätte ich paar Fragen an dich:
          1.Kannst du das Video auch auf deutsch hochladen?
          2. Eine to do Liste
          3. Verständnisfrage: Du hast ja es völlig neu programmiert, das mähen vom Roboter. Meine Frage hierzu wäre, wie ist das Mähbild(der mower fährt ja die Bahnen ab) gibt es da mählücken, zwischen den Bahnen?
          Das Projekt ist wirklich super genial und ich feiere dich vor allem das mit dem Controller und der Funktion ohne eines begrenzungsdrahtes – Hut ab!
          viel Erfolg weiterhin.

          • Clemens
            May 11, 2022

            Hallo Jürgen,
            vielen Dank für deine Nachricht.
            1) Da der Großteil meiner Zuschauer leider kein Deutsch spricht und Videos machen viel Zeit in Anspruch nimmt, konzentriere ich mich gerade auf die englische Sprache. Entschuldige. Eine To-Do Liste erstellen wir gerade im Wiki unter https://wiki.openmower.de/.
            2) Es ist alles noch in der Entstehungsphase.
            3) Die Pfadplanung basiert auf dem Code eines Open Source 3d Drucker Slicers. Dieser ist dafür zuständig die Düsenbahnen eines 3d Druckers zu berechnen, um Plastikteile zu fertigen. Hierbei ist es auch wichtig, jede Stelle lückenlos genau einmal mit Plastik zu füllen. Der Code ist in sehr vielen 3d Druckern im Einsatz und funktioniert gut. Deshalb gehe ich davon aus, dass es auch für quasi alle Rasenformen lückenlos funktioniert. Garantieren kann ich natürlich nichts.

  3. Dirk Boon
    April 7, 2022

    Hi Clemens,

    I love your idea. I would really like to have it riding my lawn. I now have one from Robomow and it really sucks.
    Spring and summer are coming so I am impatient 🙂
    Problem is, I don’t have time to build the electronics together myself.
    I can buy the Yardforce quickly. But would it be possible to buy from you the assembled/programmed electronics ? I can mount everything myself in the Yardforce and take care of battery power requirements (maybe pimp up the original battery).
    Please mail me to further discuss.

    • Clemens
      April 7, 2022

      thank you for your comment! At the moment the project is in a beta stage, which means it’s not quite ready for plug and play production.
      There will be some tinkering required for the first builds.
      The goal is, of course, to get it to a stage where you’d just buy and plug it together and it works.

      • Kevin Smith
        April 14, 2022

        Clemens, great project! Sign me up for a pre-built OpenMower when you’re ready 🙂

        • Brian Østergaard
          April 21, 2022

          Please also sign me up for a pre-built OpenMower when you’re ready. And e-mail me when ready:-)

          When I looked at robot movers, the main problems was that the robot movers was programed to have a maximum number of hours they can cut every 72 hours(I think 5 hours). So the robot mover had no problem cut my 3500 m2 if it could cut and charges with no limit.
          The only robot mover that had no limit was from Aliexpress(I was not sure it was true)

  4. Mark Humphrey
    April 8, 2022

    I like the sound of this project, I’ve been contemplating doing something similar with a golf trolley; making it drive itself based on instructions from the golfer, it could easily become super complicated though.

  5. Teddy
    April 8, 2022

    Please more information! I would like to do this!

    • Clemens
      April 8, 2022

      Thank you for your comment! I’m currently working on step by step instructions, the bill of materials and so on. Just follow my YouTube channel for any updates. If you want to know more about the deveopment, you can also join my Discord server. There is a very active discussion there. https://discord.gg/jE7QNaSxW7

  6. Diese
    April 10, 2022

    Kann es sein das der Ferrex R800Easy+ baugleich ist? Dann wäre das Projekt doppelt interessiert für mich da dieser schon in meinem Besitz ist.

    • Clemens
      April 21, 2022

      Der Ferrex sieht aus wie der YardForce SA650ECO. Diesen versuchen bereits mehrere Leute in der Community umzurüsten. Bis jetzt sieht es gut aus, ich bin mir aber nicht 100% sicher ob es klappt. Also am besten noch etwas warten.

      • VladoSL
        May 8, 2022

        I am owner of the Ferrex R800 Easy (not +) and I would like to rebuild it to your OpenMower version too.
        My mower is still on the market for about 350 Eur!
        I have found how probably my mainboard looks like 😉 https://robotgarden.se/en/produkt/moderkort-v-6-0-0/
        and looks similar – maybe even the same as in your video. So it gives me chance to follow exactly your instruction.
        If there is something I can do to ensure identity, I will do. Thank you.
        Best Regards

        • Clemens
          May 11, 2022

          it also looks to me like the same main board, so you should be fine. If you like, you can send me a picture of your mainboard (where all the text is readable) and I’ll compare it to mine.

  7. DVZs
    April 12, 2022

    /subscribe 🙂
    This is definitely something worth following. In the era of robot vacuums that work off a map I’m surprised this product does not exist yet.
    I’m in the same shoes as other before me – I lack the expertise to put one together myself, but would be willing to purchase one from you once you deem it ready. Or maybe you could start a beta tester group in exchange of usage data? 🙂
    Anyways, pls contact me when you are ready to ship the additional hw/sw components (or just a detailed manual on how to build one).
    Regards, DVZs

  8. Darren
    April 13, 2022

    Hi there,
    Are you interested assisting me in my GNSS project in Australia

  9. Steve
    April 14, 2022

    The name of the Chinese company “SUMTEC” is actually “SUMEC”, i.e. without the “T”. I went to its web, poking around (all English, no Simplified Chinese), and found additional info under the first item under the Brand”. (I do not want to type it here to avoid promoting any web or company). I bumped into the OpenMower by accident, not I am doing any, though I myself is EE/CS major, doing firmware

  10. zola
    April 15, 2022

    good job

  11. Jorge
    April 15, 2022

    Fantastic project Celemens!
    With the weather getting better this seems to be a project I would like to get involved with…
    I only seem to find the Yard Force SA650ECO and Yard Force Compact 400Ri here in the UK via amazon they go for under £400.
    I’d be happy to buy one and start contributing if you think it’s worth it 😉

    • Clemens
      April 21, 2022

      The SA650 looks promising! I have one other person on my Discord who disassembled his SA650 and for now it seems that it could be compatible – the connectors and board size are the same, but we need to figure out if they are really wired the same way. We’re not sure yet, though 🙂

  12. Lokison
    April 15, 2022

    I am very intrigued by this project. Unfortunately, as I am in the US, finding a compatible mower is proving to be difficult. DO you have any suggestions in regard to finding a compatible mower in the States?

    • Clemens
      April 21, 2022

      Yes, I noticed that it’s hard to get a compatible mower in the US. For now I don’t know which US mowers are compatible, but people in the community are working on it!

      • Brian
        April 23, 2022

        If anyone finds a compatible device in the US I would love to know

      • BD
        April 23, 2022

        If anyone finds a compatible device in the US I would love to know!

  13. Stephane
    April 20, 2022

    Hi Clemens,
    I live in Belgium and I have a small, but complicated garden (not suited at all to be mown by a “standard” wire-guided robot mower).
    Furthermore, I would be totally unable to program/build/customize one on my own.
    CONGRATULATIONS for your initiative and your passion! You started working on a very clever project and I’m sure a lot of people will be interested!
    I can’t wait to receive news from you, as soon as you are ready to start selling the inner components (or be part of a beta tester group, as DVZs suggests, this is really a good idea)!
    My (old) back would be so thankful, that I’m even prepared to buy the YardForce Classic 500 you suggest and to send it to you for customization, but I of course leave the decision up to you 🙂
    I look forward to good news!

  14. Luke
    April 21, 2022

    Hi, great post. I was wondering how you decided that Classic 500 was hackable? I am thinking if SA650ECO could also be used for something like this. Thanks!

    • Clemens
      April 21, 2022

      Thank you! I just went for it, since it seemed to have a lot of room and was cheap. Yes, the SA650 seems similar, one person already disassembled it and it has a very similar main board. We’re currently figuring out if it’s compatible. The size and connectors seem to match!

  15. Kamil
    April 22, 2022

    OMG, I’m super happy that somehow YouTube algorithms have suggested me your demo clip.
    I have the exact problem you described – multiple smaller areas to mow that are already set up. No possibility of using wire efficiently.
    I had some idea, but I never thought I come around to building something that solves it – and then you created perfect foundation!
    Followed it, and be sure I’m going to try to build one and contribute as much as possible 🙂

  16. Stephane
    April 23, 2022

    Hello Clemens,
    Hello everyone,
    I once found another robot mower equipped with a GPS and who didn’t need any wire to run. It is called TOADI (made in Belgium, I think) and it is equipped with a lot of features (4K camera, embarked heating system to prevent the LCD-screen to freeze, IR sensors to work during the night, etc.). Are they really necessary? Personally, I don’t think so, and I would rather consider these as gadgets. Its price of around 4K€ will also finish to cool down most of us.
    SO Clemens, this proves once again that you are working on a very nice and useful project :)!

  17. Stephan Neubauer
    April 26, 2022

    Hallo Clemens, ich habe das ganze Projekt bis jetzt verfolgt und bin begeistert. Leider bin ich technisch ein Laie. Gebt es jemanden, der mir beim Umbau helfen kann. Eine deutsche Anlewäre für mich sehr hilfreich. Gruß Stephan

  18. owen
    April 28, 2022

    HI Clemens

    It is great to see that you have started a project that interested for many people

    I am representative of Redback and Swift Graden tools

    we had interested in your project and are willing to provide our models for you study

    If you are interested please contact us though info@swiftgarden.com



  19. Bjoern S.
    May 5, 2022

    Hallo Clemens,
    wo bestellst du deine Platinen? Ich habe es mit eurocircuits.com dem Partner von Conrad versucht. Nach dem Export der BOM aus dem KiDac in eine .csv Datei, hat er aber viele Teile nicht erkennen können. Nun bin ich nicht der Techniker, der die korrekten Teile aus dem Katalog suchen und zuordnen kann. Ich bin schon Erfahren mit dem Umsetzen von Raspberry PI Projekten und nach deinem 2. YouTube Videos ist der Aufbau ja nun wirklich einfach.
    Daher brauche ich nur eine zuverlässige Bezugsquelle für das Mainboard und die Motor Controller, idealerweise ist auf dem Mainboard per PICO auch schon aufgelötet.
    Kannst du da weiterhelfen?
    Vielen Dank

    • Clemens
      May 11, 2022

      Hi Björn,
      ich bestelle meine Platinen unbestückt und löte per Hand. Alles andere ist auch super teuer.
      Ich hoffe bald bestückte Hardware anbieten zu können. Gerade bin ich allerdings noch dabei eine neue Motorsteuerung zu entwerfen, da die aktuelle xESC durch die Chipkrise nicht zu bekommen ist. Folge dafür am besten einfach auf YouTube oder im Discord

    • Clemens
      May 11, 2022

      Hi Axel,
      thank you for your comment! The Ardumower also uses two Ardusimple RTK modules. One in the mower and one in the base station.

      RTK GPS basically works by having two receivers and having one receiver correcting the errors the other makes. With the OpenMower you can stream those corrections from the internet (there are service providers, some free, some will cost you). Then you will only need one RTK module. I have no experience with external service providers, though. But I was told that they work just as well as having your own base station.

      • Axel
        May 11, 2022

        That is exactly what i mean, The description in the link above explain how to do this with ardumower, but my question is, if the openmower can the same thing? Maybe this would be good to explain in the WIKI.

        • Clemens
          May 11, 2022

          Yes, you can do the same thing with the OpenMower software as well

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