An oscillation generator is developed for the German geological research project KTB (continental deep drilling). The purpose is to explore the structure of the lithosphere by shearing waves. Some technical demands are similar to the requirements made on industrial servo drives: true running without cogging torques, run-up without rotor position sensor, and torque detecting from the cable terminals. Supplying the machine and measuring the data through a thin and long cable impose additional problems that must be solved.