What kind of bearings are best for consistent rotation of metal arms?

[Uname]

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.

 

[AlephZero]

Without some idea of the size and mass of the device, this is impossible to answer.

A drawing or a photograph would help explain what you are trying to do.

 

[Uname]

I'm making a compound lever, like this one:

The bearings will be used to connect the lever arms to the vertical posts holding up the arms.

The masses are fairly light - 2 kg at max, and approximately 30 g at min, so the bearings don't need to be able to handle high torques. I'll be hanging weights onto the arms of this device in various configurations until it balances with (the left arm horizontal). With the cheap ball bearing I used at first, I was able to move a weight around significantly, but still balance the lever with a bit of tapping on the device. I suspect this is because the bearing is causing issues, so what kind of bearing is best for high consistency and accuracy work?

 

[AlephZero]

I would guess the problem is friction between the two lever arms, not the bearings. And if the contact surfaces are flat as in your drawing, the resultant of the contact force can be at any horizontal position along the length of the contact area, so it's not surprising there is a range of possible weights (or positions of the same weight) that will make it balance.

You can check if the bearings are the real cause of the problem by trying to balance each arm separately.