The paper reports work in progress on the development of an innovative gearless pitch-roll wrist (PRW) for robotic applications. The PRW bears the morphology of a bevel-gear differential, its novelty lying in the absence of gears. Indeed, the PRW motivating this study is based on cams and rollers, intended to overcome the drawbacks of their bevel-gear counterparts— backlash, Coulomb friction and low stiffness. A testbed designed for parameter identification is introduced here. The paper discusses the mathematical modeling of the testbed, starting from its iconic model. The mathematical model is used to obtain the frequency response of the whole testbed, regarded as a multiple-input-multiple-output system, under the assumption that the parts of the spherical epicyclic train are rigid. The numerical values for the inertia parameters used in the model were taken from CAD models, those for stiffness and damping, as yet unknown, were estimated from a similar testbed reported elsewhere. The work ahead targets the experimental derivation of the Bode plots of the testbed, from which the numerical values of its inertia, stiffness and damping parameters are to be estimated. Moreover, having computed the stiffness and damping parameters of the testbed, the next step will be to drive the PRW at high frequencies, of the order of 1 kHz, to enable the identification of the stiffness and damping parameters of the PRW proper.
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