How RTK work in Robot Mowers


  • GNSS – Global Navigation Satellite System
  • What is RTK – Real Time Kinematics
  • RTK Base Antenna
  • Robot GNSS receiver
  • Robot Charging Station Location
  • Why Does your robot have poor Satellite connection?
  • What can you do to fix poor Satellite connection?
  • Can RTK Robot Mowers work with poor Satellite connection?




  • There are four different systems from different countries;
    • GPS – Original system from USA – 32 Satellites on 6 different plans in MEO – medium earth orbit – 12 hr orbit period.
    • Galileo – European System – 30 Satellites on 3 different plans in MEO – 14 hours orbit period.
    • Glonass – Russian System – 24 Satellites on 3 different plans in MEO – 11 hours orbit period.
    • BeiDou – Chinese System – 44 satellites.7 GEO Stationary, 10 inclined geo synchronous, 27 MEO
  • Australia being in the Asia pacific area does help us quite a lot because of the BeiDou system having stationary and inclined geo synchronous orbiting satellites in our line of sight. This gives us a significant advantage over places like the USA.
  • Typically in Australia, at any given time we can view up to 60-70 satellites if we include all the way to the horizon. And 40-50 satellites if we exclude the first 15 degrees.
  • Satellites have 3 main signals that we use to operate our robotic mowers:
    • 1 – Naming signal
    • 2 – L1 signal – older technology and does not pass through dense objects
    • 3 – L2 signal – newer technology and can pass through some objects like light to medium dense tree cover, thin plastics and timber.
    • The whole system works on the time it takes for the signal to travel from the satellite to the GPS device.
      • And this is where the issue arises with accuracy of the system.
      • Anything that affects the time it takes for these signals to reach the device will cause the positioning to be inaccurate.
      • The biggest issue here is the signal Is affected when it passes through our atmosphere and the signal is slightly delayed differently depending on the atmosphere at the time.
    • Basically, it all works by measuring the distance via time calculations and triangulating the positions of the device.
  • There are many other considerations here like the fact the earth is not perfectly round, but we are not getting onto that here. I just want to relay the very basics of how GNSS works.


  • RTK in very simple terms uses a fixed location and coordinates to help correct the time delays and use this information to correct another location that is nearby.
  • Once a fixed-point location is known by the system it can then calculate what the time delays are in the signals and then transmit those calculation to another device and then that location can be calculated with much greater accuracy.
  • For the basic systems that are used in robotic mowers, that accuracy can be down to 1-2cm. Which is just enough to ensure a robot mower is mowing the grass and not your flower bed.
  • This fixed point is established by using another device called the Base or Base receiver. This still uses the same positioning system as any other GNSS device but because it does not move at all. Its position can be more accurately calculated over a period of time.


  • Firstly, I would like to note that as a robotics person, we typically have referred to the base station as being the robots charging station. So we need to readjust our terminology of our equipment now we are using GNSS equipment. So we now generally refer to the GNSS base as the RTK Base Antenna.
  • This Base Antenna is the fixed point that your robot lawn mower will take its calculations from to get a more accurate location.
  • The placement of this Base antenna is the single most important thing you need to consider when installing your robot mower.
  • It needs to be installed in such a way that it can have direct line of sight to as much if the sky as possible.
  • You need at least 120 degrees of the sky and has 360 degree radius of view.
  • It is preferred to have more if possible and we generally recommend 160 degree view and around 300 degree radius of view if you cannot achieve 360 degree radius of view.
  • So typically this means installing the base antenna on the roof of your house or shed.


  • So at the other end you have you robot mower. Now it location is obviously dictated by your lawn.
  • The robot will need to be able to still see satellites from every location on your lawn or it simply won’t be able to navigate. This will either mean the robot will stop, or the robot will not work well and either miss some of your lawn or worse it might travel outside of your virtual boundary and that could end badly.
  • For your robot to be able to get a rough position it will need to get a good GNSS signal from at least 5 satellites that are dispersed in different directions. Typically to get 5 good signals the robot will be connected to 10 or 15 satellites.
  • But the big catch to this is that the robot needs to connect to the same satellites that the RTK Base Antenna is connected to. Hence the importance of location of the base antenna. We will get deeper into this further on.


  • Location if the robots charging station is also very important.
  • Many customers think it is ok to install this under a roof in a breezeway or pergola. This is not true, the robot will need to have a good GNSS signal when on the charger as well.
  • Typically manufacturers recommend the charging station have no obstacles 2meters on the left or right of the charger and also not be within 2 metres of a wall.
  • Now let’s be honest, most customers are likely going to want to install the charging station backed up against a wall somewhere. We generally find this to be ok as long as there is little to no obstacles blocking the robots line of sight to the satellites in the other 3 compass directions. So if the wall is blocking the view to the south, then it should have a good view to the north, east and west.
  • It is also recommended to not have anything above the charging station other than a thin plastic or timber cover.


  • This is where it all gets interesting. My previous point about the robot connecting to the same satellites as the RTK Base Antenna is not always the easies thing to achieve.
  • Let’s look at this drawing. The RTK base is installed on one side of the house and located quite low to the ground. So it cannot see the satellites that are blocked by the house. The robot however is on the other side of the house mowing. It can only see the satellites on that side of the house, and the satellites that the RTK base is connected to are blocked by the house. So in this example the robot will simply not work at all.
  • If we move the RTK base to the roof of the house, then you see it now sees all the satellites in the sky, and no matter it the robot is on either side of the house, it can see satellites that are also seen by the RTK base.
  • We call these co connected satellites and the system only works on satellites that are co connected.
  • If we also look at the same house, but with only grass to mow on one side of the house. Then it is ok to mount the RTK down low on that side of the house. You can see it has many co connected satellites and this will work ok.
  • So not only do we need many co connected satellites, the signal to the robot also needs to be a good signal.
    • There are two main reasons to get a bad GNSS signal.
      • Firstly the robot is in a location that is blocked from seeing or connecting to the satellites.
      • Also any structure, be it a shed, house wall or fence will block the GNSS signal either partially or fully.
      • Anything brick, rock or metal will likely fully block the signal.
      • Anything plastic or timber will partially block the signal.
      • Remember my point back near the start regarding the L1 and L2 signals coming from the satilites? L1 signals do not penetrate very well and L2 signals will penetrate some things, but the signal will be weaker if it does.
    • So lets look at tress firstly. In general terms if you have enough co connected L2 GNSS signals, then most trees do not stop a robot mower from working, however as the tree cover is greater and the density is greater, you will degrade the signal quality until it will no longer work.
    • We have started to grade the tree cover in this manner:
      • Light density cover like this, generally works perfectly ok and the signal quality is strong enough for the robot to remain connected and mow in mostly the same manner as it would without tree cover.
      • Medium density cover like this starts to raise questions on whether it will work or not. If the medium density cover is not widespread over the property, then it is likely to be ok, but the robot may not hold perfectly straight lines. If this medium density cover is widespread over the property, then it really depends on how many satellites you co connect to and more importantly how many of them have a strong signal.
      • High density cover like this, we generally advise that the RTK will likely not work well, unless it is just a tree or two in the middle of a mowing area and not near a virtual boundary. If near a boundary or there is widespread cover over the property, then it is unlikely that an RTK robot mower will work for you.
      • In most cases in australia we are talking about gum trees that are generally very light density and the many robots we have tested work perfectly fine.
      • For extreme cases where we are talking about super thick hedges or wind breaks, then we classify them as walls.
    • So Walls. If you have a single wall and like I mentioned with the charging station, you have a good line of sight to the other three compass directions, then you will likely be ok. If you block two directions with walls, then it becomes a problem.
      • In an L shape wall scenario, your results can be mixed. As this really depends on how many co connected satellites are seen and how dispersed they are in the two remaining compass directions. There are also parallel paths to consider that we will talk about soon. Generally, we find that L shaped walls that are less than 2mt high can be ok. But over this height there is very likely going to be an area as the robot gets closer to the internal corner where the robot will not work well, or at all.
      • With two parallel walls the problem gets a little worse, as you are now blocking the GNSS signal in two opposite directions.
      • So we have a few general rules that are often proven wrong in a positive way, but we still provide this same advice to get customers to understand that passageways between two walls is the hardest challenge for RTK based robot lawn mowers.
      • So if the walls are less than 2.4meters high we recommend a distance of 4 metres between the walls before the robot will work sufficiently to mow the area
      • If the walls are taller than this then we recommend 8-10 meters between the walls before the robot will work sufficiently to mow the area.
      • Like just mentioned we are often proven wrong here and customers report the robots working with walls closer than this, but like every poor satellite connection issue, it simply comes down to how many co connected satellites are seen, how strong the connected signal is and how dispersed the satellites are across the visible skyline.
      • We do have a good example of a user overseas with two tall walls about 8 meters apart. In this example the robot could not mow the area and furthermore, it was also unable to even pass through the area to get between the front and rear mowing area.
      • So narrow passageways between walls are certainly the biggest red flag we see with customers asking us if a RTK robot is going to be suitable for their property.
    • Now for the third and final technical issue that affects RTK robot lawn mowers. Multi path or Parallel path.
      • This one is not as well-known and basically invisible to see. But the affects are significant if you are affected by this.
      • Basically, a multi path is where a single satellite signal can be received by the GNSS receiver from more than one direction. This is caused by the signal path being reflected from another surface like a wall or other reflective surface.
      • This picture show what I mean. Because the distance is different between the two signal paths the robot or Base Antenna will reject this satellite and it won’t be used at all.
      • So this is mostly becoming an issue when the robot is close to any walls and particularly more reflective surfaces like metal or glass or taller walls.
    • So these are the reasons that you can have poor position errors or issues. This might just cause the robot to not mow in perfect lines, or it may stop the robot from working, or cause the robot to exit its designated mowing area.
    • Most robots will also stop temporarily if there is a positioning error and then as the satellites move across the sky the co connect signal strength may improve and the robot will just simply start back up and continue to mow the lawn.


  • From the above listed possible issues, the first thing to do is analyse why you think you have poor connection.
  • We use a satellite positioning App called GNSS View. This app is incredibly helpful to understand where the satellites are in relation to your location.
    • With this app you can simply view on a live directional screen where satellite are from standing in the location your robot is having issues.
    • You can also use the augmented view and physically hold your phone up and see exactly where the satellites are and see if there is any obstruction between the robot and the satellites.
    • Then do the same thing in the location that you have installed your RTK Base Antenna. Then cross reference the satellites and see if you believe you have a clear view of enough satellites that are distributed in various directions and elevations.
    • Chances are if you are having issues then there are not enough co connected satellites with a strong signal strength.
    • So the only thing you can do is decrease the obstructions from the robot and the RTK Base Antenna and their view of the sky.
      • Move the RTK Base to a location that it can see more of the sky. Again, preferably 160-degree view with 360-degree radius view if it is possible.
      • If the location where the robot has issues is heavily covered by trees in any direction, trim the trees so they have less branches.
      • Then the last thing you can try is to test the robot in the affected area at different times of the day or night. Because most satellites work on 24 or 12- hour orbits, they will be in the same location every day at roughly the same time. So test the affected area every 2 hours for a 24-hour period. You may find that it works at some times of the day and not others. If you find a good time, then schedule the robot to mow that area at that time.
    • If you think your issue might be cause by parallel path GNSS signals, then there is often little that can be done to improve the issue.
      • If practical to do you can relocate your RTK Base Antenna to the same side of the property as the problem area. As long as this still allows the RTK Base to see as much as the sky as possible then it may help to ensure the maximum amount of co connected satellites are achieved. But this still may not solve the key issue of the multipath signals.
      • you can also try testing the area every 2 hours for 24 hours as again some periods of the day may work better than other times.
      • Reducing how reflective the wall is could also work, but is often difficult to achieve. Cover the area with a softer textured surface like unpainted timber.
    • Then if there is nothing more you can do, then you may need to exclude that area from your mowing area.


  • Most if not all RTK based robot lawn mowers have some kind of other sensor to allow them to continue to work in areas that have poor GNSS signal.
    • Most use inertial measurement (IMU) to calculate where the robot is, so it knows when the GNSS signal is low it can still travel for some time. Typically, this distance travelled is fairly short before the robot will still stop as it wants to prevent the robot from traveling outside its designated mowing area.
    • Others use visual cameras to keep mowing as long as they can see grass ahead of them.
    • There are also systems coming with Radar and LiDAR sensors to do the same thing.
  • Unfortunately, at this stage our experience has shown that if your poor signal area is more than just a small space or it is on the border of the mowing area, then there is no system that will reliably mow the area without the robot either stopping or going outside the mowing area.
  • But hopefully as we receive more and more firmware upgrades, we will start to see robots managing these areas much better than they currently do.
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