That's pretty gnarly. So the discs are basically doing little inchworming steps back and forth but never has to break contact by modulating the friction? Very much a bit of cleverness turned magic.

The one thing that I notice is item 726/Fig 7./PDF pg 10, it has "with the soles and attached/embedded ultrasonic transducers". Is that maybe a different or older envisioning of this system? His shoes seemed totally normal.

Just trying to wrap my head around how much the friction can be changed by vibration, like a solid-ish state fluidized bed. Don't know it both contact surfaces need to be vibrating.