Kinematic design, motion/force coordination, and performance analysis of force-controlled wheeled vehicles

It is possible to improve the “performance” of existing active off-road wheeled vehicles by either enhancing their kinematic design to eliminate undesirable kinematic slipping, or developing optimal contact force distribution strategies that are based on an analytical understanding of the system kinematics. The above research hypothesis can be investigated by addressing the following issues: (1) System level resolution of the mobility of the vehicle and classification of singularities: Analytical 1 st order analyses that have the potential to identify appropriate kinematic variables for control purposes are investigated. Kinematic singularities along with their physical significance have been addressed. (2)  Design of a variable-length axle: A variable length axle is suggested to overcome undesirable kinematic slipping. Experiments with a three wheeled vehicle laboratory prototype with a variable-length axle are performed to investigate the kinematic model. (3) Position analysis on uneven terrain: On uneven ground, identifying the static geometry of a vehicle as it conforms to the surface requires the solving of a complex position kinematics problem. (4) Gross motion characteristics: Based on combined holonomic and non-holonomic system constraints, the gross motion characteristics of the wheeled vehicles is studied numerically. (5)  Optimal contact force allocation for systems with partial force controllability : Wheeled vehicles do not possess omni-directional (six degree of freedom) motion capability. Therefore, a subset of their contact forces cannot be controlled actively. This partial controllability situation is distinct from walking machines. These research issues are explored at a general level and are applicable to several classes of vehicles. However, the performance improvement that is mentioned in the research hypothesis is investigated specifically with respect to active and passive three-wheeled vehicles. A feedforward force control scheme is used along with active damping for some internal joints in the case of active vehicles. The controller is based on an idealistic model that assumes pure rolling of the wheel on a smooth, hard surface. A motion control strategy is used for passive vehicles. The simulation includes effects of soil work and true traction in off-road conditions.