Experiment on movement and dynamic property of driving wheel with offset steering shaft for agricultural vehicle

Abstract: A flexible chassis is a four-wheel-independent-drive and four-wheel-independent-steer electric vehicle chassis with 4 driving wheels. It can make omnidirectional motions and every driving wheel has an offset steering shaft, which means the rotating surface of the wheel is not coplanar with the steering axis, so that the chassis can make a turn using the force of the wheel. This paper presented a new type of test bench, which was built based on the working characteristics of the driving wheel, in order to resolve some key issues about the dynamics of the driving wheel based on offset steering shaft. The feature of this bench was that steering center of the offset shaft shared the same axis with the center of horizontal turntable below the wheel to simulate its moving on the ground. And a force sensor was connected between the forks of the wheel and the frame of the bench. The force analysis showed the traction force and the power for the steering of the offset shaft. And a record and display software was designed for the bench based on Visual Basic 6.0. First, we completed the whole structure design and analyzed the working principle of the device. Horizontal rotary table drove by the same driving wheel was installed, and its rotary center was the same axis with the steering shaft of the driving wheel which was connected to the frame through the bracket; the sensor was used to test the traction force of the driving wheel moving on the horizontal turntable, and keeping its levelness was supported by 4 small wheels connected to the frame. Second, a test system based on Visual Basic 6.0 was developed to show and record the data of the rotation speed, current and force. And according to the working characteristics of this bench, we analyzed the forces for the driving wheel and its fork, and a model was built and the simulation was carried out based on MATLAB/SIMULINK to make a comparison with the test data. Finally, by testing the bench, we recorded variables, such as the time, rotation speed and current of the driving wheel, and the force of force sensor. We tested the performance of the driving wheel on the bench through loading different weights on the wheel. We analyzed the indices such as the force changing progress and the time spent by stabilization of speed. The result showed that the time spent by the rotation speed of driving wheel changing from zero to stable value was not irrelevant with loading; it was 0.667 s on average. And the force, which could supply power for the offset shaft to steer, had linear relationship with loading. And when the 500 N loading was applied, the turning force was 77.24 N. The various performance indicators met the design requirement, which could make the performances satisfy the requirement of flexible chassis. The test results can provide the reference for the study of flexible chassis and also prove that the bench is feasible and efficient. In addition, the research provides the theoretical and technical references for the control design of four-wheel-independent-drive and four-wheel-independent-steer vehicles.