motor skate board

That's like asking "how long is a string".

The answer is -- I don't know for sure. If it's consumer junk, though, chances are good that it's a DC brushed motor with a drive that's either a single-FET PWM generator with a flyback diode, or a relay and a few resistors.

High-class (and possibly even less expensive in the absence of legacy parts, if not now then in 2025) would be a DC brushless motor with hall- effect feedback and a six FET driver.

For a definitive answer, get one and take it apart.

Or google it!

Wiki has a page.

BLDC motors, drivers and batteries for RC models are dirt cheap

-Lasse

I hope it includes a dead man's switch so that it doesn't continue on full power after user has fallen off, but it should not start any breaking actions not at least within a few seconds, since both the user and the board may be flying during tricks.

Of course, the bottom side must be strong and flat, so that various tricks on rails can be performed.

Of course. However, the question is hypothetical; "how would you do this?" That's a primary function of these boards - ask the opinion of experts.

Actually, I took it to mean "how are these commonly done _now_?" Which is the question I answered, BTW.

What do you mean by "six FET driver"? A hexfet? Or six discrete FETs. Doesn't make any sense to me at any rate either way.

I seriously doubt they are doing tricks with a motorized board.

It's only a skateboard; not some big industrial piece of machinery!

So use six small fets.