Roger Ebert and Three-Legged Robots

By Deane Barker on July 11, 2005

In his two-star review of “War of the Worlds,” Roger Ebert has issues with the design of the three-legged robot invaders:

If evolution has taught us anything, it is that limbs of living things, from men to dinosaurs to spiders to centipedes, tend to come in numbers divisible by two. Three legs are inherently not stable, as the movie demonstrates when one leg of a giant tripod is damaged, and it falls helplessly to the ground.

Two weeks later, in his Movie Answer Man column, Ebert was called on the carpet by someone:

Amateur carpenters are advised to build three-legged stools rather than four-legged stools. Why? Because, even if the seat is not level, all three legs will be in contact with the surface.

So — apparently forgetting that there is still no cure for cancer — Ebert called in someone from the “MIT Computer Science and Artificial Intelligence Lab” who was writing a thesis on something similar, and what follows is an interesting discussion of robotic, legged locomotion:

There is a rhythm to walking and running that may be difficult to achieve with a three-legged machine. A kangaroo is the closest thing to a three-legged animal because it uses its tail. However, its tail is not the same as its legs and the tail does not touch the ground when the kangaroo is hopping.

Ebert states that he just has excerpts there in the Answerman column and that he’s “printing [the discussion] in full on” That’s where I thought I was, but I couldn’t find the whole thing. Anyone else?

(Also, as is custom, I need to point out that I have received two personal emails from Roger Ebert over the years. This fact makes me awesome.)



  1. You are awsome indeed.

    The amateur carpenter argument is bogus, a stool is static and not generally used as an attack device. Think about when ATVs (and farm tractors) used to have 3 wheels. They were very unstable. And that instability was the with all three wheels intact.

    But as for the movie (which I have nto seen) I think the 3-legged concept works to a primitive human awareness that these machines and their creators are unnatural.

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