Traversal in off-road conditions for Unmanned Ground Vehicles is highly relevant for defence applications, with an increasing amount of research being put into the field. A central part of the autonomous traversal is path following, where there currently exist many stable controllers. However, conventional path following controllers often relies on ideal vehicle models that make assumptions about the terrain that are no longer valid in off-road conditions. Therefore, research is needed into how conventional controllers are affected by off-road terrain and if extending the vehicle model with relevant parameters can improve the performance. In this paper, a controller based on Active Disturbance Rejection Control and a controller based on Instantaneous Centre of Rotation are tested against a conventional controller in off-road conditions. Results from simulations illustrate how the conventional controller is affected by variations in the vehicle’s rotation centre while the proposed controllers have improved performance when simulating rough terrain conditions. Real world experiments were conducted in uneven sandy terrain, where all of the controllers showed decent performance, but the proposed controllers had the lowest cross-track error. Future Unmanned Ground Vehicle operations can improve performance by using the proposed controllers when the vehicle is experiencing rough terrain where the Instantaneous Centre of Rotation is considerably shifted from its ideal location. On the other hand, the conventional controller should produce decent performance in moderate conditions. Further research is needed to understand what types of real world conditions make the performance of the conventional controller significantly decrease, thus justifying the use of one of the proposed controllers.
The usage of Unmanned Ground Vehicles (UGVs) in defence application is increasing, and much research effort is put into the field. Also, many defence vehicle producers are developing UGV platforms. However, the autonomy functionality of these systems are still in need of improvement. At the Norwegian Defence Research Establishment a project for developing an autonomous UGV was started in 2019 and use a Milrem THeMIS 4.5 from Milrem Robotics as the base platform for achieving this. In this paper we will describe the modifications made to the vehicle to make it ready for autonomous operations. We have added three cameras and a Lidar as vision sensors, for navigation we have added a GNSS, IMU and velocity radar, and all sensors get a common time stamp from a time server. All the sensors have been mounted on a common aluminium profile, which is mounted in the front of the vehicle. The vision and navigation sensors have been mounted on the common aluminium profile to ensure that the direction the vision sensors observe is known with as little uncertainty as possible. In addition to the hardware modification, a control software framework has been developed on top of Milrem’s controller. The vehicle is interfaced using ROS2, and is controlled by sending velocity commands for each belt. We have developed a hardware abstraction module that interfaces the vehicle and adds some additional safety features, a trajectory tracking module and a ROS simulation framework. The control framework has been field tested and results will be shown in the paper.
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