My own 2¢...
I think we all tend to lump at least 4 interrelated but distinct physical processes under "wobble", myself included. They're hard to tell apart just by looking at them, and they can occur in combination. But there are relatively simple ways (like the paintbrush method) to tease some of them apart.
And if the goal is to eliminate all wobble in a top, their causes must be addressed separately.
Unbalance wobble: Here, I borrow Iacopo's term for the motion I still believe to be "whirl" in the engineering sense. But be that as it may, if the paintbrush method or one of its variants works as intended, at least some of the top's wobble is of this kind. Its verified presence is incontrovertible evidence of unbalance, and the only cure is to rid the top of both static and couple unbalance.
Tip-related wobble: Closely akin to unbalance wobble, this type arises when tips are misaligned, inadequately supported, or misshapen at the contact patch. The only cure is to fix the tip.
Elastic wobble: This kind of wobble is probably very uncommon outside the LEGO realm. By design, LEGO's proprietay ABS plastic has a lot more elasticity than metal or hardwood or any number of other plastics. The stresses of abrupt spin-up and release can excite elastic structural oscillations of a twisting or flapping nature in many LEGO top rotors. I think we'd all describe the resulting visual effect as "wobble". Stiffening up LEGO tops to suppress elastic wobble consumes a lot of my time.
Gyroscopic nutation: A normal top motion, but some tops are more prone than others. Can be excited, sustained, or exacerbated by other forms of wobble. Conversely, nutation can feed energy into tip-related and elastic wobble, but nothing can excite unbalance wobble in the absence of, well, unbalance. Nutation remedies include fiddling with mass properties and getting smoother launches through practice or the use of a starter.
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Topic: So what is wobble, really? (Read 1151 times)