An Open Source Robotic Lawn Mower With RTK GPS, OpenMower

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Robotic mowers are becoming more prevalent in some areas, thanks to the decreased cost of motors and the necessary control electronics, which has been made possible by the rapid advancement of modern engineering. However, they still appear to be fairly stupid in many cases, little more than a jacked-up bump-and-go with a spinning blade. [Clemens Elflein] has given a cheap, dumb mower a brain transplant using a Raspberry Pi 4 and a Raspberry Pi Pico for real-time control. [Clemens] has dubbed this OpenMower, with the goal of creating an open source robot mower controller with GPS navigation and RTK for added precision.

The donor robot was a YardForce Classic 500, and after looking at the control PCB, it appears that many other robot mower models utilise the same controller, making them openmower compatible. The Pi 4 and Pico, as well as an ArduSimple RTK GPS module (with a reported navigational accuracy of 1 cm) and three BLDC motor drivers for the wheels and rotor, are all housed on a bespoke mainboard. Everything is based on modules that plug into the mainboard, greatly decreasing the project’s complexity. The Yardforce mower platform has a good build quality for a low-cost mower platform, with connectors everywhere, making OpenMower a plug-and-play option. The user interface on top of the mower was also functional, with a modified PCB beneath it displaying several push buttons in the proper locations.

Motor control is provided through the xESC project, which offers low-cost FOC motor control via a serial link with the host controller. This is a worthwhile investigation in and of itself! [Clemens] is utilising ROS for the software, which includes low-level robot control, path planning (using code from Slic3r), and kinematics restrictions for object avoidance. The video below demonstrates how easy it is to use the machine: simply drive it around the edge of the lawn with a handheld controller, indicating where impediments such as trees are, and then set it going. The mower can even mow numerous lawns at once, automatically switching between them.

The mysterious TK with an interesting take, another employing RTK GPS for good (or maybe bad), and very likely the jankiest one we’ve seen in a while, which employs a LoRa base-station to communicate RTK corrections, are all examples of robotic mower projects. That last one should be avoided at all costs.

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