[wwalker3]

The guy whose thesis this was comments on it here: http://www.reddit.com/r/math/comments/ebql6/double_inverted_...

I had guessed they were using visual sensing because of how the two halves of the pendulum were painted in contrasting, bright colors, but I was wrong. There are angular sensors at the joints of the pendulum, and a position sensor in the wagon at the bottom. The control system also needs the velocities of the parts of the pendulum, which it gets through a state observer (http://en.wikipedia.org/wiki/State_observer).

The interesting part for me was how the control system stands the pendulum up: it figures out the potential energy the pendulum will have when upright, then jerks the wagon around to add that amount of energy into the system as kinetic energy, then guides the system around a constant-energy landscape until it's upright. Pretty clever!

[TorKlingberg]

I wonder if the frequency of the "jerking around" is hard-coded for the lengths of this particular pendulum. It would be cool if it could automatically determine which movement patterns add energy to the system after trying for a while.

[liuliu]

The visual sensing is quite impossible due to the high speed of its movement. Any camera that can capture the color information at that speed is expensive.

[palish]

So how much would it cost to build one of those robots?

[wwalker3]

It looks like a big linear motor like in the video is probably $1000 to $2000 dollars. Angle sensors are pretty cheap (just a few bucks). Then you'd need an A/D-D/A board to control it with ($500 to $1000).

[hartror]

And a smart PHD student, which are pretty cheap I hear ;)

[sdfghjkjhg]

Although the 'smart' ones are something of an endangered species

[mkramlich]

don't worry, one day some smart PhD student will create a robot that's smart enough to replace smart PhD students