## 1 Introduction
[15], which is a modular, cost-oriented quadruped built for research purposes. In modular robots, there may be a set of constraints that reduce the robot construction budget. Furthermore, if the robot is supposed to fulfill more than one objective, the best strategy is to build the platform to be as modular as possible, being adaptable to (almost) any situation. Considering what was mentioned above, two main objectives for the construction of the robot presented in this article were the cost reduction--thus, designing a low-cost robot--as well as the maximization of its modularity. Another major objective is focused on energy saving, in order to increase the robot autonomy, with the inclusion of a low-power mode. Development of realistic simulation models of robotic systems represents an extremely important stage for refinement of the robot, as precise operation can only be assured by finely tuning the variables related to control strategies, dynamics, and the robot mechanics themselves. Simulation tools are valuable for testing purposes due to allowing modeling of a variety of situations for assessment of the performance of the robot, while avoiding damaging the real robot. Whereas the presented platform is a quadruped with several coupled, non-rigid joints, the realistic simulation model significantly reduces the probability of the robot suffering unforeseen damage, as well as decreases, for example, the control algorithms' testing. Available simulators with incorporated dynamics for robotics include Gazebo, Webots, and SimTwo [16]. Several publications report the use of simulations to test legged-wheeled robots. [PERSON] et al. [17] employed a Gazebo-ROS (Robotic Operating System) framework to validate the wheeled-legged motion control scheme for CENTAURO. A 3D dynamic simulation was conducted by [PERSON] et al. [18] to validate the developedmethodologies, namely, for posture control of the robot. [PERSON] et al. [19] evaluated their proposed control strategy for stable walking with cosimulation. The present work is the continuation of the work published in prior articles [20; 21]. Each leg uses almost the same physical configuration. However, there was an evolution to improve the robot's mechanical robustness, sensor data acquisition, data communication, leg synchronism, and robot kinematic control. Despite these, the robot maintains the same low-cost, low-power, and modular concerns and methods that were previously introduced. The complete robot is described, as well as the improved mechanical design and hardware. The software used to control the robot, as well as the communication approach, is also depicted. The built prototype is controlled across the \(x,\ y,\ \text{and}\ z\) axes, and is capable of moving omnidirectionally. The robot can also be controlled across the roll and pitch axes, improving its locomotion on unsmooth terrain. Each leg is controlled individually; the non-rigid joints are controlled using state-space controllers, while the hip joint is controlled using a PID position controller with a trajectory smoothness function, and the wheel is controlled through a PID speed controller. A realistic simulation model of the presented vehicle has been developed and tested in the SimTwo simulator software. This free robotics simulator provides an environment with incorporated dynamics and features the possibility to model different types of robots--from manipulators to mobile robots. Throughout the article, the mechanical design and construction of the robot will be presented, and both the individual and complete control strategy for each leg and the robot are described. The applied communication technique will be detailed, along with the message flow between the robot and the legs. The process followed for obtaining the models for the motor and joint used, and the models themselves, will be described. The kinematic model will also be presented.