I must go to feedback and correct motor position if arm, and for the head I must use a mechanical solution like:
No. All you need is to implement a form of negative feedback.
For example, if the motor moves past the right of your desired position, turn the shaft left; and vice versa. With the negative feedback, the shaft/arm will hold (likely vibrate slightly around the target), mechanical limitations not withstanding.
One area of leading edge research, almost directly comparable to what you are trying to do, is to use brushless motors as steppers.
It is definitely doable. However, getting the whole system stable and responsive isn't simple.