Robin2 does make a point that if you wanted to try to make a stepper act like a hobby servo, you could, but would need to add an encoder.
I am not sure why there is such a desire to mis-use a stepper and try to make it into something other than what it does best.
if you put a stepper on the arm, home it, then move 'x' steps, the arm will move 'x' steps repeatedly for hours on end.
if it hits a brick wall and the arm does not flex, then it might miss a step, or even 100 steps. but that would mean a lot of things gone wrong.
and maybe improper selection of parts.
to start and get a feel for the motion, here is one with hobby servo's
what no one mentioned is that industrial servos are the step up above steppers. they have a VERY large motor, into numbers of horsepower, not fractions. They
have external encoders, and a very complicated driver. used on high-end metal working machines, laser tables, large milling machines, work centers etc.
I would probably limit steppers to something smaller like a Bridgeport mill.
spend some time on youtube and watch what others have done. pretty neat stuff
lots of hobby servo types:
if normal operation made a stepper based system miss steps, tehn this would not work
here is a CNC mill that is retro-fitted with steppers.
will run for hours without missing steps while cutting metal parts.
did I mention run for hours without missing steps ?
I am not sure what the Arduio community has such a poor understanding of steppers in general.