well, I used the system in this following way:
- the left-of-neck limiting switch was triggered, so robot knows that could only turn right
- the set-point of turning write is chosen,
- motor is commanded to turn, and reading pot, until pot<=x (x being the set-point)
I actually tested this system and not that bad, but one thing is really awful and that is the main concept I was for: keeping the load.
If I command motor (still not by PID) to keep on a position, say, if potx turn left, the noisy movement is not only coming from the fact that I didn't use a PID, but also from the pot being a <1$, too noisy type.
I guess - and look for your kindly guides to get sure - that beside PID I must change to a pot type which is less noisy but same time not on cost of 30$ as the question was "turning dc motor to servo", to try to pay less than the servo cost.
Now if the original question is someway wrong (impossible to turn dc motor to hold the load like a servo but for less price), then well, I have nothing more to say, or ask 