Trying to figure out the Segway...

[sanddrag]

I was exactly in your same mindset a couple years ago. So I tried to build one. After I was done, I would have gladly just paid 5 grand. If you try making one, you will quickly learn why it costs so much. It's purpose may not be worth 5 grand but all the parts and development that's in it certainly is.

[Pat Fairbank]

I would imagine the speed limiting function further complicates the balancing algorithm.

When you're approaching the maximum speed for the key you're on, or when you're otherwise approaching the maximum power the motors can put out (like when facing a strong headwind) the motors sort of put on a burst of acceleration to get the base of the Segway further forward in relation to the handlebars, so that if you wanted to accelerate any more you'd have to lean right over the handlebars (which would prompt a stick-shake warning).

So I'm going to leave speculation on how it works to people who are more qualified to answer.