When a spherical motor with multi degrees of freedom like a human shoulder joint is in practical use, a lot of systems with multi degrees of freedom will be compact, lightweight, and high performance. However, the motors are controlled by open-loop, as there are no good rotor posture sensors. This paper reports the basic experimental results of a developed posture sensor with two mouse sensing devices. The basis transformation matrix is used to represent the rotor posture. At first, researches of the posture sensors for the spherical motor are reviewed. Among the previous work, select a posture sensor with two mouse sensing devices. Show the advantages of using the basis transformation matrix to represent the rotor posture. The basic ideas for getting the posture from the data of two mouse sensing devices are presented. A posture sensor with two mouse sensors is developed and tested.