# Hybrid Model-Based Analysis of Underground Articulated Vehicles Steering Characteristics
## 1 Introduction  
With excellent maneuverability and efficiency, underground articulated vehicles (UAVs) are widely used in the processes of drilling, transportation, supporting and charging, which are of decisive significance to the production of underground mines [1; 2; 3]. The increasing depth of mines leads to significant local environment problems, such as high temperature and high humidity, which cause greater difficulty for mining, and potentially threaten the safety and health of the underground staff. Therefore, autonomous UAVs are urgently needed. Because of the specialty of steering, the lateral precise control of UAV is an important issue [4; 5], which is usually based on the dynamic model and steering characteristics of the UAV. The steering characteristics reflect the control performance, and are the main means to evaluate the handling stability and path tracking of the vehicle [6; 7; 8]. However, the simplified models and ambiguous steering characteristics of UAVs hinder their precise control. In recent years, much research has been directed towards the precise modeling and control of UAVs [9; 10; 11; 12]. [PERSON] [13] et al. established a steering model of UAVs based on the relationship of velocity, centroid and handling stability. The simulation results showed that the velocity andcentroid were the key parameters leading to oscillation and instability. [PERSON] [14; 15] et al. established a simplified three degree of freedom (DOF) model to analyze the snaking motion of UAVs and studied the relationship between lateral stability and steering characteristics. [PERSON] [16] et al. established a kinematic model on the basis of a dynamic model, and the steady steering and pulse steering processes were analyzed. [PERSON] [17; 18] et al. studied the effect of kinematic parameters on a motion planning system, and the kinematic model was used during the process of modeling and control. [PERSON] [4] et al. established a 12 DOF dynamic model of UAV and uncovered the instability area considering the influence of bulk modulus of hydraulic oil. Based on the instability results, an Ackman-based hierarchical controller was designed to improve the stability of UAVs. [PERSON] [19; 20] et al. designed a nonlinear model predictive controller based on the kinematic model of a UAV, with a maximum error of 0.14 m.  
The above studies focused on the stability of UAVs, and different models have been established to analyze the influencing factors on the stability. In addition, strategies were also designed to control lateral motion or improve the accuracy of path following. These achievements greatly improve the stability and control accuracy of UAVs. However, some shortcomings remain to be addressed; for instance, dynamic models have been greatly simplified for the control and analysis of UAV, e.g., the hydraulic power steering system has been separated from the dynamic model of the frames or even ignored. The involved kinematic model in control strategies has generally been based on steady steering, while the transient process and steering characteristics were ignored. Moreover, the trajectories of the front and rear frames were considered to be the same during the system of path following. In reality, the trajectories are different in the transient process of steering, and the process would also be different under different working conditions. Motivated by these shortcomings, we attempt to analyze the steering characteristics based on a hybrid model to uncover the relationship between dynamic steering and the response of frames. Several contributions are summarized as:  
1. A hybrid model including a dynamic model of articulated frames and a model of a hydraulic power steering system is established. 2. A field test is carried out to verify the dynamic model in time and frequency domains. 3. The steering characteristics of a UAV, which involves the effects of load and velocity, are revealed based on the verified model.