A recent tour of a vintage WWII era aircraft carrier reminded us how difficult navigation was before the advent of GPS. It used to be the work of experienced people to look at the sun or the stars and use huge books to find out a ship’s position. Now just ask your phone to listen to a few GPS satellites and you’ll have a level of precision unmatched by other systems. But GPS is sometimes not enough. You can only locate yourself within a few meters with conventional GPS. The new L5 band, which is not yet present on all satellites, can take you to about 30 cm. But if you need more – up to about 1 or 2 cm – you have to use special techniques, grouped together as GNSS improvements. [Viktor] wanted an Arudino-based lawnmower, but wanted to use more conventional GPS techniques along with Ultrawideband (UWB) ranging tags.
Given that the range anchors are in the mowing area, we’re not sure why the mower even has GPS other than geofence, so you can’t start autonomous operation until you’re within range of the tags. The three anchors are placed in a triangle. So if the robot knows the distance to each tag, with some math it can locate itself within the area fairly accurately.
The mower not only needs to know where it is, it also needs to learn where to mow. To do this, you have to manually drive the mower around the perimeter via Bluetooth.
Overall a nice looking project. When you need the highest accuracy with GPS, it is common to use a base station and compare the phase of the received signals from the base station to those from the robot. This lets you know very well where you are in relation to the base station, but doesn’t tell you any more about where you are exactly than if you were using regular GPS. Of course, if you know exactly where the base station is, that also works.
Many mowers that we see use a stock motion base. This isn’t the first time we’ve seen an Arduino-based mower.
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