I'm working on a project which has two rotating metal arms. These arms need to move in very consistent ways (that is, when I hang weights from the arms, they should behave in the same way every time). I'm looking into using bearings to hinge the rotating arms to the rest of the frame. What kind of bearings are most needed here, or should I not use bearings at all? I tried some ball bearings that I found sitting around, but they didn't provide the necessary consistency. Thanks in advance.