Previously, this problem was solved quite simply. In the circuit of the windings included additional adjustable resistances of high power. Thus, the working current of course decreased, and with it the speed of rotation of the shaft decreased and the speed of rotation. But the whole trouble is that significant thermal energy was released on the resistors and, with intensive use, they quickly burned out. In addition, the moment fell on the shaft, and the electric motor could not crank the mechanism attached to it. In engines equipped with a frequency electric drive, these problems are fully resolved. But the whole point is that the servo is a rather complicated and expensive device and its mass use is very costly. That is why specialized devices for smooth launch have gained popularity, which in comparison with drives are quite simple and inexpensive. At the same time, they fully cope with their functions.