RRR-robot design: basic outlines, servo sizing, and control

The RRR-robot project aims at a manipulator-like system (with three rotational degrees of freedom), to test a variety of advanced nonlinear control strategies. Since for high-speed tracking of complex trajectories, Coriolis and centrifugal torques form an essential part of the occurring nonlinear effects, the main requirement of this robot is to highlight these velocity dependent torques. In this paper the outlines of the manipulator design are discussed. By exploring the main requirements two important features of the RRR-robot are introduced: unconstrained rotation in each link (e.g., by using sliprings) and the use of direct-drive servos. Several types of direct-drive servos are discussed and a choice is made to use brushless DC motors. The iterative dynamic optimization problem of choosing appropriate servos is solved by using a rigid-robot model implemented in a symbolic manipulation program. This program is also used for simulation and evaluation of both open and closed loop behavior.