3D-printed torsional mechanism demonstrating fundamentals of free vibrations

Commercially available turn-key systems are expensive and require substantial lab space, making it harder to accommodate many in vibrations laboratories. This study presents a low-cost, compact, and portable torsional mechanism incorporating multiple rotating disks and a long thin rod supported vertically with bearings and fixed supports at the top and bottom ends to study the modeling of systems using experimental data. The mechanism consisting of a rod, disks, bearing, and disk supports, and the base is built by 3D printing using thermoplastic PETG. The long, thin rod in this mechanism serves as a torsional spring. The equivalent stiffnesses of the 2 DOF system can be changed by adjusting the vertical position of the disks with respect to the ends, thereby shortening or lengthening the effective twist length of the thin rod. The overall dimensions of the mechanism are 6 inches in height, 5 inches in width, and 2 inches in depth, and the expected cost including the experimental setup is around USD$30 if an Arduino is used for data acquisition and $170 if equipped with a National Instruments external data acquisition card. Learning objectives of the lab course utilizing the proposed mechanism are identified. The free response data are collected for a single degree-of-freedom system using an external data acquisition card and potentiometer and unknown parameters of the system are determined by system identification. Mechanism unknown parameters are calculated using system identification and a theoretical model is compared with the experimental data