Depend on your load, small load you can use stepper. For big load, I use 1-1 1/2" KW AC motor with gear reducer or you can buy ready to use AC motor with adjustable speed (with gear). I use the latest one (cheaper and constant speed and torque can be achieved), max is 7 RPM. I use them at .5 to 1.5 RPM (use timing belt to reduce speed since speed must be constant for welding quality) for welding casing and wellhead. My load max is 1 ton.