A Low-Cost Fatigue Tester for Maker Spaces

Abstract

The fatigue testing machines (FTMs) commonly available in the market can cost upwards of a hundred thousand euros and require a pneumatic or hydraulic power supply. The pricetag and infrastructural needs of such devices make them unfeasible for maker space applications. A low-cost FTM designed for modularity and flexibility and constructed using easily accessible components can provide a viable alternative. The problem statement is addressed by identifying motors as the right actuation choice and selecting the motor type to accomplish the required operation based on the selection chart developed in this thesis. A hybrid bipolar stepper motor is selected for its precision, speed and torque characteristics. An h-bridge driver circuit is discussed for controlling motor rotation for high current applications. AutoDesk's TinkerCad model illustrates the motor control circuitry and the microcontroller programming necessary to control the motor. The control system is simulated on MATLAB/Simulink. Using a step input controlled PWM, position and speed control, and an h-bridge driver circuit to manage rotation, the motor is driven at different speeds for a variety of test scenarios. The motor has a step angle of 1.8 degrees. The shaft angle graphs demonstrate a cycle frequency of 0.5 Hz for unidirectional and bidirectional motor control. The required 70 Nm torque range, 0.5mm stroke size, and motor speed are dependent on the mechanical coupling used with the actuation system. The results validate the system's adaptability and flexibility for varying fatigue tests and require further research and practical experiments to develop a feasible standardized low-cost alternative for the growing maker space ecosystem.