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An impact rotary motor based on a bulk piezoelectric torsional actuator with grooved helical electrodes is proposed. The prototype actuator, with dimensions of Φ 8 mm × 10 mm, produces a maximum torsional angle of 0.035° with a driving voltage of 2200 Vp-p. Its first torsional resonant frequency is 32 kHz with the fixed-free boundary condition. The rotational speed of the developed motor is proportional to both the amplitude and the frequency of the driving voltage in low frequency range. With a saw-shaped driving voltage of 1400 Vp-p at 8 kHz, the motor can rotate at a speed of 22.5 r/min with a braking torque of 0.1 mN·m, and the stall torque can reach up to 1.6 mN·m. Although its maximum efficiency is less than 0.1%, the motor produces a rather small step angle with a large driving torque. It is suitable for ultrahigh precision positioning.