| Skid steer mobile robots are mechanically simple, highly maneuverable, and capable of maintaining traction on a variety of terrains. These benefits have been used in many applications requiring mobility on uneven ground, stairs, and even vertical surfaces. Skid steer mobile robots (SSMR) with climbing capabilities can be used in manufacturing applications such as welding, cutting, surface treatments, and inspection. When performing a manufacturing task, the robot is required to move a tool along a specified trajectory over the climbing surface. Therefore, understanding the kinematics and dynamics of these machines is important in both the design and operation of SSMRs intended for manufacturing and other applications. When considering the kinematics and dynamics of SSMRs, it has been established that the motion constraints are functions of the dynamics. However, the general practice in SSMR modeling generally treats these constraints at the kinematics level by assuming or selecting constant slip rates from empirical data, or removes the constraints by casting the system into a null space of the constraints. This paper will demonstrate a method to solve for the slip parameters directly from the equations of motion. The method is enabled by defining the constraint forces through a specified friction model. This approach is assumed appropriate for manufacturing applications in which the climbing surface is a metal with predictable, homogeneous properties. The slip parameters will be solved subject to a specified trajectory and position along the path. The model is validated through comparison with results obtained from a Mobile Robotic Manufacturing System (MRMS) equipped with magnetic tracks for vertical climbing observed with an experimental vision based data acquisition system. The model will be demonstrated for its use in providing improved estimations of position or in the design of climbing SSMRs. |
