I was one lucky bugger in my youth in that I had a buddy who worked at HP and brought me surplus gizmos [I thought] he acquired for dollars...

As I recall, he brought me two flatbed plotters, two 8.5in floppy drives, an ISA HPIB card with full manual (and BASIC instructions!), and a whole slew more that I was not at all worthy of.

I loved that plotter... watching two interlocked doughnuts form from seemingly-random trapezoids was mesmerizing. I've saved (and modified) and replotted that file countless times over the past 25+ years. From the much more studio-apartment-friendly HP7475A [paper-fed] plotter I eventually acquired, to the wall-hanging plotter made of legos, to the Silhouette vinyl-cutter I got from Goodwill, to #The Artist--Printze wherein I wrote code to treat an inkjet like a pen-plotter...

But nothing beat those old flatbeds, which I STUPIDLY took apart.

They were exceptionally fast, and precise. The mechanics, if I understand correctly, we now call "Core-XY" but were far superior to anything I've seen since. (I later figured it out, from memory, and managed to extend it to three dimensions with legos and pulleys... long before I'd ever heard the term Core-XY). I liked that mechanism so much, after I finally pieced-together in my mind how it worked literally two decades later, that I tried to design a "business card" plotter around it #2.5-3D thing...

Somehow STUPIDLY I took both those flatbeds apart. STUPIDLY. And STUPIDLY only managed to keep a few random pieces...

Including the stepper motors, which are amazingly strong and fast, as I recall, and the weird oil-filled dampeners which nearly look like nothing more than "spare no expense" "eye-candy" yet I remember how smooth those stepper motors were, and fast, and maybe somehow those seemingly physically-useless oil-filled flywheels on bearings actually made that possible.

Anyhow... WAY side-tracked. Man I was STUPID back then. Just downright stupid.

Watching it switch pens was beautiful in and of itself. Such precision and delicacy and yet such speed. What the HE** was I thinking when I scrapped them?!

....

In addition to the bipolar [4-pin] steppers, I also somehow managed to keep a stepper driver-board...

And when I was finally smart enough to understand what a bipolar stepper was, it occurred to me that.... waitaminit. How could 2 bipolar steppers be driven by only 8 power transistors?!

An H-Bridge is 4 transistors... And you'd need two for two windings in each motor! That'd be 16 power transistors, not 8!

...

I mean, it's not like I *really* sat and thought about it, but it's been percolating for probably 20 years, until just now.

And now I feel a bit stupid, again. But not nearly as stupid as I feel thinking about younger-me scrapping those amazing machines.

Anyhow, a big build-up for something probably obvious...