The wheeled three-link snake robot is a well-known example of an underactuated system modelled using nonholonomic constraints, preventing lateral slippage (skid) of the wheels. A kinematically controlled configuration assumes that both joint angles are directly prescribed as phase-shifted periodic input. In another configuration of the robot, only one joint is periodically actuated while the second joint is passively governed by a visco-elastic torsion spring. In our work, we constructed the two configurations of the wheeled robot and conducted motion experiments under different actuation inputs. Analysis of the motion tracking measurements reveals a significant amount of wheels' skid, in contrast to the assumptions used in standard nonholonomic models. Therefore, we propose modified dynamic models which include wheels' skid and viscous friction forces, as well as rolling resistance. After parameter fitting, these dynamic models reach good agreement with the motion measurements, including effects of input's frequency on the mean speed and net displacement per period. This illustrates the importance of incorporating wheels' skid and friction into the system's model.

翻译：轮式三连杆蛇形机器人是利用非完整约束建模的欠驱动系统的著名实例，该约束防止车轮的横向滑移（打滑）。在运动学受控配置中，假设两个关节角直接作为相移周期性输入被规定。在机器人的另一种配置中，仅一个关节被周期性驱动，而第二个关节由粘弹性扭转弹簧被动控制。在我们的工作中，我们构建了轮式机器人的两种配置，并在不同驱动输入下进行了运动实验。对运动跟踪测量的分析揭示了与标准非完整模型中使用的假设相反，存在显著量的车轮打滑。因此，我们提出了修正的动力学模型，这些模型包含了车轮打滑和粘性摩擦力，以及滚动阻力。经过参数拟合后，这些动力学模型与运动测量结果达到了良好的一致性，包括输入频率对平均速度和每周期净位移的影响。这说明了将车轮打滑和摩擦纳入系统模型的重要性。