Aspects of the technology employ sensors having high speed rotating mirror assemblies. For instance, the sensors may be Lidar sensors configured to detect people and other objects in an area of interest. A given mirror assembly may have a triangular or other geometric cross-sectional shape. The reflective faces of the mirror assembly may connect along edges or corners. In order to minimize wind drag and torque issues, the corners are rounded, filleted, beveled, chamfered or otherwise truncated. Such truncation may extend the length of the mirror side. The mirror assembly may employ one or more beam stops, light baffles and/or acoustic/aerodynamic baffles. These sensors may be employed with self-driving or manual driven vehicles or other equipment. The sensors may also be used in and around buildings.