Junya Yamakawa

Mobility Characterization of Planetary Rover in Reduced Gravity Environment

This paper describes effects of gravity on mobility performance of wheeled rovers for future lunar/planetary exploration missions. A series of model tests of a wheel‐terrain system were performed on an aircraft during variable gravity maneuvers, and it became clear that slip of the wheel becomes high when the gravity is less than 1/2G. In addition to the flight experiments, the same model tests were performed in a laboratory on the ground (1G condition). The experiments were demonstrated with variable wheel loads by using counterweights. As a result of the on‐ground experiments, the mobility performance under low wheel load conditions was found to be improved contrary to the flight experiments. In case of the flight experiments, not only the wheel load but also bearing in the terrain changes with respect to the gravity level, while only the wheel load changes in case of the on‐ground experiments. Thus, running under a reduced gravity condition becomes difficult because the terrain generates higher rolling...

A Method of Driving Force Allocation to Reduce Slip Loss for Multi-Wheel Vehicles with Independent Wheel Drive (Formulation and Numerical Simulation)

A method of optimal driving force allocation to the wheels of multi-wheel vehicles is proposed. Practical application of in-wheel motors to vehicles expands the capability of vehicle control and efficient drive. The determination of necessary driving force on each wheel is essential factor for efficient drive especially for multi-wheel vehicles with individually controllable wheels. Optimal driving force allocation to each wheel has been formulated by minimizing the slip loss done by all the tires due to ground contact. Solving the equations with the specifications of an eight-wheel vehicle under several conditions, optimal driving force allocation and the combination of optimal steering angles were obtained. The result of the numerical simulation was found to be useful for target driving force on each wheel for efficient drive.

Steering and Driving Systems and Turning Characteristics of Multiaxle Vehicles

This paper presents a mathematical model and numerical analysis for multiaxle vehicles operating on level ground. Considering possible factors related to turning motion such as vehicle configuration and tire slip velocities, equations of motion were constructed to predict steerability and driving efficiency of vehicles. Turning radius, slip angle at the mass center, and each wheel velocity are obtained by numerically solving the equations with steering angles and average wheel velocity as numerical inputs. To elucidate the turning characteristics of multiaxle vehicles, the effect of fundamental parameters, vehicle speed, steering angles and type of driving system, are examined for a sample of multiaxle vehicles. Additionally, field tests using a full-scale vehicle were carried out to evaluate the basic turning characteristics on level ground.