Abstract :
The limitations of existing pivoted arms are outlined, followed by brief details of some past and present radial tracking arms. The advantages of very low tip mass cartridges tracking at <0.2 g, and the design requirements of suitable arms, are discussed as an introduction to the principles and design of a radial tracking arm with a side thrust of <3 dynes at 33¿ rev/min (`Trutrack¿), in which the weight of the arm, head and counterweight is supported by a float immersed in silicone fluid.Details of setting-up techniques and methods used to seal and package the liquid filled trough to withstand transport shocks of 100 g are given.The calculation and measurement of inertial forces resulting from eccentric and warped records, wow, frequency and damping of various vibrational modes of the arm are described. Details of the magnetic repulsion bearing system used in the device, with some performance curves, are given, and the problems of designing reliable low drag liquid signal contacts discussed. Materials and techniques used to ensure long term reliability of the device are described.
