These motors have very high inductances (16 mH or more) and this drives up the max voltage that must be applied to obtain maximum power. Gecko's rule of thumb is that the max voltage (V) = 32 sqrt( I (mH) ). These large inductances can give high holding torque, but you want to be able to move them, which requires faster charging/discharging of the coils, and lower inductances. I bought the G540 with a 48V supply, then shopped for motors with ~2 mH windings. I found mine at Kysan.