8 A team from the University of Córdoba in Spain is developing an autonomous tractor with three different steering modes, allowing it to drive in straight lines, make turns efficiently, and shift modes in response to its trajectories. The Sergius robot tractor can autonomously perform agricultural tasks in fields of woody crops such as olives. The researchers, with the Rural Mechanization and Technology Group at the University of Córdoba, Sergio Bayano and Rubén Sola, designed the vehicle from the ground up, in collaboration with two companies charged with its mechanical manufacturing and programming. “On the national market, there are some small autonomous vehicles that can be applied to agriculture, but there were none with a tractor’s functionality,” said researcher Rubén Sola. “This vehicle has the same functions as a tractor, but is groundbreaking in that, in addition to being autonomous, it features two independent self-levelling axles with steerable wheels, which makes its control more versatile.” The front or rear steering uses single axle turns; reverse front-rear steering, in which both axles turn, provides a smaller turning radius; and a new hybrid steering system where the front axle turns, and the rear axle also turns, but by half the angle of the front axle. This allows the vehicle to move forward in a straight line but at an angle to improve the trajectory stability in navigation while preserving the versatility of mechanical steering. To evaluate the different modes, the tractor was tested in an intensive olive grove, where it was determined that the inverted mode with the front and rear axles turning in different directions was optimal for completing turns precisely, and the hybrid mode was the most suitable for straight sections. The tractor is able to shift between its different steering modes according to the needs of its manoeuvres. “The technology we have incorporated is necessary for autonomous navigation: two Lidar sensors, one in the rear and one in the front; an inertial unit, which measures acceleration and inclination; a digital compass, to monitor the tractor’s direction; and a high-precision GPS system,” said researcher Sergio Bayano. “All the programming was carried out using the ROS (Robot Operating System) environment, which, being open source, allows other algorithms to be implemented and code to be shared with other research teams.” The vehicle employs a diesel and hydraulic propulsion system as agricultural machinery demands a lot of power and torque. It is controlled via two interfaces, one for the hydraulic system and the robot’s different actuators, and a second for its programming and decision-making. Ground vehicles Dual axle steering for autonomous tractor April/May 2025 | Uncrewed Systems Technology The Sergius autonomous tractor (Image courtesy of The University of Cordoba)
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