# Susceptibility Modeling of a Rubber Track for Lightweight Mobile Robots
## 2 Track Susceptibility in Simulation Models  
In order to properly shape the running gear, simulation tests [27; 30; 31; 32; 33; 34] are widely used. They make it possible to estimate the drive torques necessary to overcome the motion resistance, obstacle negotiation ability [35], maneuver performance resistance [33], and energy consumed by the robot [20]. Despite the impact of rubber track susceptibility on many aspects of the robot's functionality, it is not always taken into account. In fast real-time simulations, in order to shorten the calculation time, the structure of the track belt may be omitted or simplified [36; 37]. Running gear is presented as a system consisting only of driving wheels. The belt adds to the hull weight. To increase the accuracy of the track-terrain contact surface, there are models where the shape of the tracked running gear is obtained by using an increased number of overlapping wheels to form an almost continuous contact surface with the ground [33; 38]. An alternative solution is also to use the non-deformable track model [35; 39]. It allows the track to perform on the ground, developing tractive force, but track deformation in reaction to the ground is impossible. This model allows for relatively quick determination of the parameters of driving straight, negotiating small, simple obstacles, and even turning with a fixed radius. The problem, however, may be situations of point contact with the ground, e.g., curb or stair climbing [37]. This type of model is also used to predict the motion parameters of robots when performing maneuvers [33]. The track model, taking into account its deformation ability, can be achieved by the coupled multibody dynamics-finite elements method model [40] or the finite element method [41; 42]. A model using a system of wheels and a track belt with a structure divided into a finite number of elements was used, e.g., in the research [42] of the rubber-tracked running gear of a farm tractor. Considering the elasticity of the rubber belt, its deflection under its own weight was used to model parameter identification. By using finite elements, it is possible to give the elastomer material non-linear, hyperelastic properties. In this way, its deformations and stresses while driving can be reflected with high accuracy. The disadvantage of the method is its long simulation time. Therefore, despite the possibility of using the FEM method in dynamic simulations, it will not always be fully practical. Another track modeling method is to digitize the belt into a finite number of elements (links) connected with each other by constraints (joints), defining its motions by restricting degrees of freedom [43; 44; 45]. This method is widely used in metal track modeling [28; 46]. It allows deformation of the track in accordance with the adopted constraints as well as a more accurate verification of which of its elements remain in contact with the ground. It is especially useful when simulating overcoming terrain roughness. Three connection methods are most often used between track links: kinematic joints, force constraints, and constraints with plastic deformation ability [44]. The simplest type of track-link connection is one with kinematic constraints. They provide movement in an established angular range, but they do not reflect any forces occurring in the constraint. This method was used in research on heavy vehicle dynamics [28; 45; 46; 47]. The simulations and experiment results for acceleration when driving over small obstacles were compared [48]. The simulation data is compatible with experiments at low speeds. At higher speeds, the omission of the damping constraint properties resulted in too high simulated vertical vehicle body acceleration. This indicates the need to take into account the elastic-damping properties of the track belt constraints. These properties may be described by general force constraints between track links.