# Estimation of Skid-Steered Wheeled Vehicle States Using STUKF with Adaptive Noise Adjustment
###### Abstract  
Skid-steered wheeled vehicles are commonly adopted in outdoor environments with the benefits of mobility and flexible structure. However, different from Ackerman turning vehicles, skid-steered vehicles do not possess geometric constraint but only dynamic constraint when steered, which leads to motion control and state estimation problems for skid-steered vehicles. The controlling accuracy of a skid-steered vehicle depends largely on feedback state information from sensors and an observer. In this study, a 3-DOF dynamic model using a Brush nonlinear tire model is built, first, to model a 6 \(\times\) 6 skid-steered wheeled vehicle in flat ground driving conditions. Then, an observer using the unscented Kalman filter with a strong tracking algorithm and adaptive noise matrix adjustment (AN-STUKF) is established to estimate vehicle motion states based on the 3-DOF dynamic model. Finally, the experiment is carried out in three different driving conditions to verify the accuracy and stability of the proposed method. The results show that the AN-STUKF method possesses better accuracy and tracking rate than the traditional UKF, and the phenomenon of ICRs shifting forward of the skid-steered wheeled vehicle is also verified. skid-steered wheeled vehicle; UKF; adaptive noise matrix; strong tracking; ICRs +
Footnote †: journal: Applied Sciences  
_Article_  
Estimation of Skid-Steered Wheeled Vehicle States Using STUKF with Adaptive Noise Adjustment  
[PERSON]  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) [PERSON]  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) [PERSON]  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [PERSON]_ADDRESS] (S.Y. ); [PERSON]_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) Xufeng Yin  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [PERSON]_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) Xufeng Yin  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) [PERSON]  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (S.Y. ); [EMAIL_ADDRESS] (X.Y. ); [EMAIL_ADDRESS] (X.L. ); [EMAIL_ADDRESS] (Q.L.) [PERSON]  
1 National Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Beijing 100081, China; yuansihu@bit. High nonlinearity and instability are also significant challenges to state estimation for skid-steered vehicles. To meet the requirements of a control system, the vehicle moving states are important information for vehicle control. In view of the special conditions the skid-steered vehicle frequently works in, for example, the complex electromagnetic environment on a battlefield, the estimation algorithm is based on the local sensors (encoder, IMU, etc.) instead of GNSS and other sensors. The focus of this study is to develop an observer to estimate motion states of a skid-steered wheeled vehicle including velocity, yaw rate, and slip parameters. Firstly, a 3-DOF dynamic model using the Brush nonlinear tire model is developed to model the skid-steered wheeled vehicle dynamic characteristics. A kinetic model based on wheel rotation rate and slip rate is also developed to calculate the sideslip angle of each tire and longitudinal slip rate. Then, based on the dynamic model, the UKF observer is built to estimate the vehicle motion states.