A Wheel-leg Biped (Two-legged) Robot – Prototype 01
The first prototype of the wheel legged biped robot is shown in figure 28. The robot designed from the Solidwork with all the basic requirements which is knee joints, hip joints, wheels and the head.
The traditional inverted pendulum balance principle involves oscillating the centre of mass of the inverted pendulum in an equilibrium position using the chassis movement to achieve dynamic balance. However, in the case of the robot in this paper, the objective is to maintain balance while changing the robot's height, which is a dynamic process. To achieve this, the paper focuses on finding a way to maintain the centre of mass (COM) of the robot's body on the axis AF, which is vertical ground and passes through the centre of the two-wheel axis.
The robot comprises several parts, including waist link, thigh joint, thigh link, calf joint, calf link, wheel joint, and wheel link, each designed with detailed dimensions. The paper introduces the simplified structure of the robot and imports it into Simscape for simulation after establishing the relevant reference coordinate system and axis in Solidworks.
The left and right legs of the robot are synchronized in the case of changing height. Therefore, in the subsequent joint constraint relationship derivation, the top surface of the robot is always kept in the equilibrium position. As a result, the IMU can be directly installed on the top surface of the waist link for measuring the robot's orientation and maintaining its balance.
The Simscape code is shown in the figure 29 once it import from the Solidwork. PID controller is a control algorithm used in many systems to achieve a desired output. PID stands for proportional, integral, and derivative, which are three components that make up the controller. The proportional component of the controller provides an output that is proportional to the error between the set point and the actual output. The integral component integrates the error over time, which helps to eliminate any steady-state error. The derivative component provides an output that is proportional to the rate of change of the error.
In the case of the wheel-legged biped robot, the PID controller is used in dynamic balance control to maintain the balance of the robot while changing the height. The tilt angle error is defined as the difference between the set point (0) and the measured tilt angle. The tilt angle refers to the angle of the robot body with respect to the vertical ground. The PID controller uses this error to adjust the control inputs to the robot to maintain balance.
The proportional component of the PID controller adjusts the control input proportionally to the error. The integral component adjusts the control input based on the integral of the error over time. This helps to eliminate any steady-state error. The derivative component adjusts the control input based on the rate of change of the error. This helps to stabilize the system and reduce overshoot.
By using a PID controller in dynamic balance control, the wheel-legged biped robot can maintain balance while changing its height. The controller adjusts the control inputs to the robot based on the tilt angle error, which helps to keep the centre of mass of the robot body always on the axis AF during height changes.
Figure 28: Solidwork view of the wheel legged robot
Figure 29: Simscape code of the wheel legged biped robot
This presents a method for changing the height of a bipedal wheeled robot while maintaining dynamic balance. The robot is designed to have its centre of mass constrained to an axis that is perpendicular to the ground and passes through the centre of the two wheels. By doing this, the robot is able to change its height without losing balance, thereby allowing it to operate in a larger vertical space.
To validate the feasibility of this method, constructed a simple simulink simulation environment and performed some experiments on a prototype. The simulation and experiments showed that the proposed method is effective in allowing the robot to change its height while maintaining dynamic balance.
Overall, the method presented has potential applications in various fields, such as search and rescue, inspection, and surveillance, where a robot with the ability to change height while maintaining balance can be useful.
30: Isometric view of the wheel legged biped robot
Designing a realistic robot with all the working dynamics and components is a complex process that requires knowledge of mechanical engineering, control systems, and robotics. The first step in this process is to define the specifications and requirements of the robot. This includes the desired size, weight, mobility, and functionality of the robot.
Once the specifications are defined, the next step is to design the mechanical structure of the robot. This involves creating a 3D model of the robot in a CAD software such as Solidworks, which includes all the components such as motors, sensors, and power supply. The design must take into consideration the strength, rigidity, and weight of the materials used, as well as the placement and orientation of the components to ensure proper functionality.
After the mechanical design is complete, the next step is to simulate the robot using a software such as Matlab's Simulink environment. This involves creating a model of the robot that includes all the dynamics and components, and simulating its behaviour under different conditions such as movement, external forces, and sensor inputs. The simulation allows for testing and refining the robot's design before building a physical prototype.
Once the simulation is complete and the design is finalized, the next step is to build a physical prototype of the robot. This involves assembling the mechanical structure and integrating all the components such as motors, sensors, and power supply. The control system is also integrated, which allows for controlling the movement and behaviour of the robot.
Overall, designing a realistic robot with all the working dynamics and components is a complex process that requires knowledge and expertise in multiple fields. The process involves defining specifications, designing the mechanical structure, simulating the robot's behaviour, building a physical prototype, and testing and debugging to ensure proper functionality.