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Image On Friday CMU announced via press relase the creation of the "Ballbot" (original, I know). It’s a robot that dynamically balances on one steel ball. It was picked up by several robot websites and was also featured on RocketBoom.

That’s all fine and good, until someone cries "fowl!"  

I just want to note that they bought their own pre-assembled IMU. That takes nearly all of the challenge out of this project.

Theo goes on to say:

Don’t believe me? Take a look at the papers. The entire control system is simple LQR. They’ve added some PI control to correct for some frictional effects, and both coefficients were tuned experimentally.

Translation: It’s not that hard. A PI controller takes about four lines of code, and experimental tuning involves grunt work, not real science. Here is a link to the IMU they use.

While I’m not sure if I’d be as harsh as Theo is with them, I definitely don’t think it was worth all the hype or the press release. Come on CMU, show a little humility!

Update: Theo, made some good comments below.

One response to “CMU's BallBot – Scientific Advancement or Just-Another-Robot?”

  1. Theo (Ted)

    Well, they do do a little bit of science in the design of their LQR controller. They build a simple model of the system and show that their controller is a valid controller for a system modeled as such. The experimentally-tuned PI controller was just added afterwards to get rid of some frictional effects. (the “I” is the important part; it serves as an internal model that deals with the frictional damping by accumulating extra control energy)

    However, none of this is cutting edge control science. A truly sophisticated handling of this robot would include an input (what they built was purely for stabilization/regulation; it is not meant to track an input) and build an appropriate nonlinear controller. (note: for an inverted pendulum like this, the nonlinearities aren’t that great. Gravity adds a sinusoid function, which is globally Lipschitz and looks pretty darn linear when you’re very close to the equilibrium; thus, this problem isn’t even sufficiently nonlinear to be interesting)

    So some real science was done here… But it was classroom science. There was no contribution. Nothing *new* is being done here.

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