The experiments were performed using the one degree of freedom manipulandum in our laboratory. For these experiments, the device was configured such that we could easily change the inherent mechanism dynamics, particularly, the physical damping of the motor shaft. A fluid-filled viscous damper was coupled to the motor shaft via steel tape, allowing the device to be implemented either with or without damping (See Figure 8). With the damper attached, the inherent damping of the device was approximately 0.22 Nm-sec/rad.
The display is powered by a DC brushless motor mounted to a sturdy table so that the motor shaft points upward. Attached to the shaft is a crank handle (r~0.15m) which the user may grab with his/her hand. The motor shaft is equipped with two encoders (8000 counts per revolution and 900,000 counts per revolution) for position sensing. Motor currents are supplied by a PWM amplifier, and voltage inputs to the amplifier are provided by a 12-bit A/D converter.
