Maybe, the part that goes from slippery to sticky with ultrasound is beneath the rubber disks and when there's no load they just rotate freely?
And because of this, the person above is stepping on the "spinning surface" (the "base" surface of a cylinder) of these tiny disks, instead of the curved surface like a normal wheel or some industrial conveyor wheels (as someone linked below, https://www.youtube.com/watch?v=PRS0Uj2WdpA ).
So in a sense, they're not "rotating like rotating wheels" despite being wheels/disks.
BTW, it looks like they also can adjust its axis angle slightly (less than 30 degree), which I imagine is also crucial to how it works.
Feels like a very mechanically-simple strategy, but hard to make durable / safe from fingers (and detecting "skin" vs "shoe" doesn't seem like something you can make foolproof) / that would hurt to fall onto.
The drawback of this is that it requires a firm contact point like shoes to work. You wouldn't want to walk in socks on this. You also couldn't have a performer lay directly on the surface and transport them across the stage, nor allow them to have baggy clothing near it. Running would be difficult from a balance perspective, not to mention holding a wheel at a particular tilt would require quite a bit of force if someone runs on it. It's going to have a very particular use case for Disney.
But anyway, thanks for improving my English.
To mrtksn: yeah I think your original post is pretty clear. But there are indeed other comments in this thread that are confusing the two.
In my mental model its wheels attached in different way that rotate around an axis perpendicular to the ground. I call in wheels because moves the things around.
I'm really confused by the confusion. Isn't it obvious on the video that its cylindrical objects that can be considered thick disks and wouldn't all disks rotate on the round surface around the axis?
From the close-up shots, you can clearly see them rotating and changing inclination.
By changing inclination they can control the contact surface of the rotating wheels and as a result control the direction of your movement. Very clever and simple but might be dangerous(you wouldn't want to have your pinky stuck between load bearing rotating wheels) and prone to tear and wear due to the high dynamic friction.
However, if there's actually a way to make it sticky or slippery with ultrasound then you can get away with a partial rotation back and forth while turning it sticky in one direction to push the objects in that direction and turn it slippery to reset its own position and get ready for another push. This probably will make it quite safe.