# Design and Lateral Stability Analysis of an Attitude Adjustment Tractor for Moving on Side Slopes
## 6 Conclusions and Future Works  
A tractor with an attitude adjustment function is designed and developed to traverse on side slopes. The lateral stability is also investigated while taking configuration/posture into consideration. Inspired by the traditional tractor, a method to adjust attitude is described. Corresponding mechanisms are also designed to adjust the tractor's posture, adapt terrains, and transfer power. This tractor exhibits two locomotion modes. In the first mode, it can work under uneven terrains while keeping the four wheels in contact with the ground without needing sensors. In the second mode, the tractor can adjust the roll angle in the case that slopes or larger obstacles are encountered. Meanwhile, a leveled attitude is obtained to ensure drivers' comfort. Thus, this four-wheel-drive tractor is able to maintain stability in various situations (especially side slopes and uneven terrains) with a simple control system. The tractor presented in this paper thus has provided new insights into the design of tractors with multiple motion modes, which has potential application in the fields of hilly and mountainous terrains. Tractor stability against a lateral overturn is known to be determined by multiple factors [1; 36]. Exterior factors such as the ground conditions (slope angle and obstacle shape and height) cannot be controlled [2; 37]. Thus, interior factors can be changed to adjust tractor stability. Fortunately, factors such as the moment of inertia, wheelbase, COG position, track width, ballast weight, implement position, and tire properties affecting tractor stability have been clearly explored in previous studies [1; 8; 13; 38; 39; 40]. However, attitude adjustment technology, which can actively adjust a tractor's configuration and posture, has not been considered in previous studies. With specific attitude adjustment  
Figure 10: Lateral stability in theory and test modes. mechanisms, a tractor can adjust its configuration and posture to enhance its stability and trafficability. Therefore, this study also analyzes the effects of posture change on tractor stability on side slopes. A mechanical model relating the configuration of the tractor to its lateral stability is presented. A static study for evaluating the lateral stability of a tractor possibly suitable for working on hilly and mountainous terrains has been made. This developed model allows to treat an attitude adjustment tractor and forests the instability conditions with active inputs. Meanwhile, several conditions are not considered in the proposed model, e.g., steering radius, speed, tire deflection, and soft road. Taking the designed tractor with attitude adjustment mechanisms into consideration, the above model and the stability conditions have been implemented in a MATLAB simulator and they have been validated by means of an experimental emulator. With the designed attitude adjustment mechanism, the designed tractor can actively adjust its roll angle. This tractor can also level itself when the angle of the side slope is less than 15.79\({}^{\circ}\). The results of numerical simulation show that lateral overturn stability increases while adjusting the configuration. lateral instability limit angle (\(\theta_{lim}\)) increases from 33.42\({}^{\circ}\) to 44.87\({}^{\circ}\). A prototype is developed and the reliability of these models is examined through bench tests. The results of numerical simulation show similar tendencies to those of the experiments. Overall, adjusting the tractor's attitude can reduce lateral overturn. The approach developed here provides an effective way to enhance a tractor's lateral stability. In addition, the leveled posture can be considered as an appropriate configuration to ensure the drivers' comfort and stability. Future work will be devoted to the extension of the model in the (quasi-)static and dynamic study for evaluating the stability of a general tractor with posture change.