Mechatronic design, dynamic modeling and control of six legged robot

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Dr. Harmati István
Department of Control Engineering and Information Technology

The paper describes the necessary preparations for the construction of an RHex-like robot, which includes movement simulation, motor dimensioning, the design, realization and simulation of the robot’s leg, the construction of the Test Bench measuring device and its validation results, along with the optimization of the robot’s walking parameters and spring constant, and the circuit design of the robot.

The RHex is a bio-inspired six-legged robot with one actuator for each leg. The leg’s geometry is a half circle, which can completely turn around. For this reason the robot’s movement is similar to that of a wheeled robot. Despite its mechanical simplicity the robot can run, turn, jump, climb stairs, and do a backflip.

As a prerequisite for the construction, I conducted the analytical modeling and movement simulation of the robot and the validation of its leg. I determined the robot’s dimensions, mass, locations of its centers of gravity, the spring constant of its leg and its natural frequency using CAD modeling and finite element analysis.

The combined simulation of the walking algorithm, motor control and mechanics was done in SimMechanics environment with the imported CAD model. Based on the results of the movement simulation I selected the appropriate motor and accumulator, which I added to the CAD model. I optimized the walking parameters, energy losses, walking speed and the leg’s spring constant using particle swarm optimization.

The optimal spring constant and mechanical endurance of the leg can be calculated from the weight of the robot. The paper presents multiple variations for realizing the leg with different materials and processing techniques.

The validation of the robot’s leg was done by using Test Bench, which is a partially self-developed measuring device. Test Bench has four main parts: leg hitting device, driving part, measuring circuit and a computer interface. The measurements can be divided into static and dynamic measurements. With the former we can calculate the leg’s spring constant and endurance, while the latter is used for calculating the natural frequency and damping.

The last segment of the paper describes the design of the driver circuit for the robot’s leg.


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