We have shown that zero-stiction flexure bearings are great for dealing with warps
, but do we really need anything advanced for the vertical axis? Shouldn't we just put a miniature ball bearing there and call it a day?
Yes and no. While a zero stiction, zero play flexure bearing would perhaps be an overkill, we need to keep in mind that some of the intense vertical movement caused by disc's warps does translate into the horizontal movement
. It's not as big in amplitude, but still noticeable.
Another important role of the vertical bearing(s) is location and load bearing (excuse the pun). The entire weight of the moving arm assembly rests on them. They also need to keep the vertical axis, well, vertical.
Here, the choice must be made. Ball bearings with low starting torque often have quite a bit of play. This slack can result in the vertical axis rocking. If we use high precision bearings that keep the axis strictly vertical, we'll lose some of the starting torque (stiction) performance. What is more important?