I see it on page 17 (18 including the MIT front page)
It's a linear motor, more like a speaker voice coil without cone.
I'm blind. In my defense, I was looking for a linear-shaped linear motor, and took that for a spinning doodad.
alt Hacker News
I'm blind. In my defense, I was looking for a linear-shaped linear motor, and took that for a spinning doodad.