When flying over the United States, Australia, and a few other vast and relatively empty parts of the world, strange circular formations can be spotted. These are typically center-pivot irrigation systems, an effective way to irrigate crops if efficient use of space is not too big of a priority. Keeping these massive machines in a straight line is an interesting engineering problem, though, and [rctestflight] built a miniature version of his that works on the same principle but mows his lawn instead.

These systems work as semi-independent sections that are flexibly coupled at either end. The control scheme initially used here was to drive the outermost set of wheels at a constant speed, and then use limit switches at each coupling inside of that to drive inner sets of wheels once the outer set passes a setpoint. Eventually a potentiometer-based proportional controller was installed in place of the limit switches. With some other drivetrain issues sorted out it was on to building the mower attachment. This uses a pair of pivoting precision knives mounted to motors that ride along a carriage attached to any one of the linkages of the center-pivot system. Limit switches keep the carriage riding back and forth cutting the lawn as it traverses the grass.

With the system in place, [rctestflight] set out to optimize it mostly out of a desire to tinker with a thing that he had built. The challenge for him is that his location in the Pacific Northwest is generally very damp, so in addition to corrosion and other water damage on various parts, there were also issues of mud complicating the way the wheels navigated the terrain, as well as the plant growth being fairly rapid and often impeding the process of the robot as well. One of the perks, though, was that the circular area was already largely carved out thanks to some of his earlier projects testing the durability of RC cars.