How the robotic lawnmower works using the STIHL RMI 422 P as an example

  • Jun 29, 2022
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I was tired of mowing the grass every week in my summer cottage and I decided to explore the market for robotic lawn mowers. In advertising and videos on Youtube, there was no answer to three main questions, so I had to study everything "on my own skin".

How the robot lawnmower works using the STIHL RMI 422 P as an example

There were three things I was interested in about mower robots:

- can the robot move over an uneven area with bumps, bumps and holes, or is it only for ideal lawns;

- is the robot able to mow dense wild grass, or is it only for lawn grass;

- is it possible to use the robot not every day in automatic mode, but only once a week when visiting the dacha (in our conditions, it is dangerous to leave a robot on the street - they will steal it, and even climb into the house, since the owner is such "rich").

In order to find out the answers to this question, I asked the company Sledgehammer. RU give me a mower to test some robot. A week later, I had a huge box with a rather expensive robot in my dacha. STIHL RMI 422P.

Most robotic lawn mowers cost from 35 to 150 thousand rubles. Almost all of them work on the same principle. A boundary wire is laid on the site (it and pegs for attaching to the ground are included in the delivery of the robot), with the help of which the territory where the robot works is determined. The beginning and end of the wire are connected to the base (by the way, until the wire is connected and the base is not included in the network, the robot refuses to start at all). Those places inside the mowing area where the robot cannot climb (flower beds, pools, etc.) are fenced off with a wire, moreover, in those places where two fragments of wire are folded together and go back and forth, the robot passes freely without feeling restrictions.

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Most robots have only two sensors: a collision sensor (this can be either a movable bumper or an internal sensor) and a rain sensor. Very expensive robots have an ultrasonic obstacle sensor, for some robots such a sensor is sold as an option.

Almost all robots move randomly: the robot reaches the wire and turns to an arbitrary angle. The site map, as far as I know, is built only by Bosch robots, but judging by the reviews, the result of their meaningful movement is often even worse than the chaotic one of other robots.

Any robot mower uses a charging base, while it can find it (reaches the wire and rides along the wire until it meets the base), charge and continue mowing after charging.

Typically, robot mowers have two large drive wheels (20-22 cm) and one or two rollers (8-9 cm). Stihl has two rollers.

Many manufacturers, to the detriment of the patency and quality of the mowing, make the robot as safe as possible - so that it cannot injure the hand of a child lying on the grass or cut off the tail of a cat. To do this, the clearance in the front of the robot is lowered to 2.5 cm and the knives are protected as much as possible by combs and metal elements. All this leads to the robot getting stuck and the robot getting clogged with grass. It seems to me that the situation when a small child lies on the grass, and a stupid cat puts its tail on a mower is almost unbelievable. Conventional robots have a clearance of 5 cm, and as soon as the robot meets something thicker, it immediately turns around.

As you can see, Stihl has no protection, which is good. In this model, the grass is cut by two metal knives on a disk, the cutting width is 20 cm.

Other models often make three interchangeable double-sided knives that rotate freely on a disk. Pictured is a Worx Landxscape 600 LX790.

The robot can mow on schedule. In the simplest robots, the schedule is set automatically: the plot area is set, on the basis of which it is calculated how many days per week (from 2 to 5) and how many hours (from 2 to 10) to mow. You can only set the start time. For more advanced robots, the schedule can be configured in more detail. Of course, the robot can also be started manually (or until you stop it, or for a specified number of hours, depending on the model).

Many robots have a setting for mowing zones - the point of the boundary cable is programmed where the new zone begins. After that, you can start mowing certain zones or a sequence of zones (to find the desired zone, the robot simply rides along the wire for a memorized time, and then starts mowing).

There are robots equipped with Wi-Fi. They are configured and controlled from the application on the smartphone (you can start and stop mowing, send the robot to the base, set the schedule). Perhaps the main advantage of the robot's Wi-Fi is notifications about work and problems. If the robot gets stuck (and it will definitely get stuck), a push notification will be sent to the phone.

Let's get back to the Stihl robot and the answers to my questions.

This robot does not have Wi-Fi, everything is controlled through a large LCD screen. There is a zone setting, a lot of additional "chips" like searching for a broken wire.

The main impression: the robot "rushes like a tank." He turned out to be completely unconcerned with my bumps, pits and bumps. The first time he got stuck was when he ran into a pit so that one wheel hovered over it and the other hung in the air. This is where all the stupidity of the robot manifested itself: it simply endlessly turned the wheels and the mowing disc, thinking that it was mowing. I was surprised that the programmers did not think of making it so that if the robot “rides to the wire” for too long, then something went wrong. A couple of times the robot got stuck, finding itself in a corner of thick grass - it began to "poke" left and right, but could not pass in any way, and then it did not work out even backing away. But in general, the robot drives through an unprepared area and rarely gets stuck. All places of potential jamming can be corrected.

My second question was about the density of grass that the robot can mow. Mows dense wild grass "with a bang", but it is important that the grass is not high, it can get stuck in it. In general, the instructions for any robot say that before using it, the lawn must be mowed with a conventional mower. Ideal for a robot when it cuts a little each time, not letting the grass grow. For the lawn itself, this is also good, because the robot does not collect grass, but leaves it on the lawn (when cutting small ones, they quickly rot, turning into fertilizer, and large ones can be seen and they will rot longer).

The main question is whether it is realistic to use the robot only once a week, removing it when no one is in the country. Answer: not always. As I wrote above, it is desirable that the grass before mowing is low (ideally - up to 5 cm). In May and early June, the grass grows by 10 centimeters in a week. The robot will be able to mow such grass, but it will inevitably get stuck sometimes.

The second point is mowing time. A rectangular lawn without obstacles, measuring 6.3 x 3.2 m (~ 0.2 acres), Stihl mowed in 30 minutes, it will take him about two hours per hundred square meters. Five acres - about 10 hours, and if there are many obstacles, most likely longer.

I made a video in which I showed how the robot mows grass of different heights, how it parks at the base and much more.

https://www.youtube.com/watch? v=vS68gHT2Jrc

In general, everything turned out much better than I could have imagined. The robot is able to mow not only ideal lawns, but also an ordinary crooked suburban area with wild grass. You will have to tinker with laying the boundary wire, and probably somewhere later you will have to re-lay it. It is desirable that the robot works on a schedule and mows at least once every 2-3 days. You need to be prepared for the fact that any robot will sometimes get stuck. But still, the robot is able to make sure that the site does not need to be mowed manually.

Peace for everyone!

© 2022, Alexey Nadezhin

For twelve years I have been writing about technology, discounts, interesting places and events. Read my blog site ammo1.ru, in Learn, Zen, Mirtesen, Telegram.
My projects:
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#robot#lawn mower#country house