An apparatus comprises a housing, a bearing member, and a transmission system. The housing has a channel in communication with an opening at a first end of the housing and a first surface at a second end of the housing. The first surface is substantially perpendicular to a rotation axis through the channel. The bearing member is capable of rotating in the channel around the rotation axis. The bearing member has a second surface substantially perpendicular to the rotation axis and substantially parallel to the first surface. The transmission system is coupled to the first surface and the second surface. The transmission system has a transmitter and a receiver. The transmission system is capable of emitting an electromagnetic radiation in a beam that is capable of being received by the receiver, while a rotation occurs between the transmitter and the receiver about the rotation axis.