A 3D measurement device is provided that includes a base and a measuring head that can be rotated relative to the base about a first axis. A light emitter is provided which emits an emission light beam and a light receiver which receives a reception light beam. A control device determines the distance to an object. The mirror assembly is provided includes a motor housing and a shaft coaxial with the second axis. A motor is provided having a rotor and a stator, the rotor being coupled to the shaft, the stator coupled to the motor housing. A support structure has a body and a sidewall, the sidewall defining a hollow interior region that receives the rotor and the stator, the support structure further having a slanted section. A reflecting mirror is coupled to the slanted section for deflecting the emission light beam and the reception light beam.