What a pretty wheel! Love it!! And I'm loving the cast iron wheel. Is that a leather drive belt? Is the wheel an antique?
I ask, because just a couple of weeks ago I bought a new treadle-driven sweetie. Not a spinning wheel, but a treadle sewing machine, and the cast iron wheel and leather drive belt are very similar to what's on my sewing machine! Whoever built your wheel must've been very familiar with treadle sewing machines and used their mechanism as a model -- and maybe the parts, too!
eta: (and forgive me for slightly hijacking your post, but seeing your wheel inspired me) I thought I'd throw in a photo of my sewing machine (cabinet currently closed) to show the treadle. The wheel is off to the right, so a different orientation than on your wheel. But gets me to thinking, those sewing machine treadle bases can often be found easily on Craigslist, etc., without the sewing machine head installed. People sometimes make those into tables, but I'll bet a very clever person could take a treadle sewing machine base and somehow make themselves a spinning wheel, if they looked at your wheel as an example. Those old treadle bases are often not expensive. I paid only $25 for my entire sewing machine. Also, if it's a leather belt and you ever need advice about replacing it, let me know. I had to replace the leather belt on my sewing machine. Wasn't too hard but helps to have someone talk you through it.