The LA is a knitter. Some yarn does not come ready to knit with. However, ball winders are available, some motorised.
The LA realised that she had married me. She therefore commissioned me to make for her a ball winder, using K'Nex, since it had been posted elsewhere. To this end, we procured the following resources:
My first attempt was... overcomplicated.
This monstrosity never got tested, because I realised that I'd overlooked how to transmit torque properly, and thus I could get the required two-axis spinning action with a single shaft. The key was in fact the ability of the gears to free-float.
Version 2 was distinctly less overblown:
The big wheel turns, causing the small cog to turn with it. This rotates the platform. Meanwhile, the vertical shaft is held immobile, and the wheel atop it engages with the spindle cog, causing the bobbin to rotate whle the platform it's mounted to also rotates. Hopefully, once I've figured out precisely how to run this thing, it will produce balls of yarn which can be centre-pull or outside-pull, and will do so at roughly a fifth the cost of a motorised one. It actually cost similar to a hand-wound winder, but is That Much Cooler simply because it's something I built.
Directions are available on request; if you share them, please credit me for them. I put a lot of thought into this device!