I'm curious about something for most of the "bug style"
walking robots. (This question really doesn't apply to the
RoboOne style biped robots.) Almost all of the bug-style
walkers have their legs articulated the same way: The
entire leg pivots around a vertical rotary axis at the hip
joint. Also on the hip joint is a horizontal rotary axis
that lets the entire leg move up and down. Past this
there's typically at least one other knee joint, also
usually oriented horizontally.
Earlier when someone posted about the Boston Dynamics "Big
Dog" robot, someone made a comment about how odd the leg
joint arrangement was. It's odd for a robot, but not for a
dog. The primary joint is a horizontal rotary axis,
oriented parallel to the length of the body. This lets the
leg swing in closer to the body or out, farther away.
Mounted on this is another rotary axis that pivots with the
rest of the leg. It's neither always vertical or always
horizontal, but with the leg directly under the robot it's
mostly a horizontal rotary axis that lets the leg swing
forward and back.
It's this hip design (a very good analog to what you see on
a cat or a dog) that lets the Boston Dynamics robot have
such nimble feet and respond so well to a disturbing force
(e.g. a swift kick to the ribs, as you can see on the videos
on their web site.)
The only other place I've seen that close an analog between
nature and robot was the study done at MIT on the mechanics
of cockroach leg joints. It's not nearly as obvious as one
might think, and bears little to no resemblance to the
hexapod arrangements available from most robotic supply
houses. Among other things, the hip joints more closely
resemble those of BigDog.
So I'm curious about two things: One, why haven't more
people tried this hip orientation? For accelerating from a
dead-stop, it places more of the loads along the leg rather
than across it (much easier on the joints!)
Second, and more important, did I just ask the "but why?"
question that's going to get me out of mini-sumo and into my
next phase of exploration in robotics?
In a way I hope the answer to the second question is no. I
love building mini-sumo robots. In another way I hope it's
yes. Walking robots pose REALLY neat questions I'd like to
I guess I really hope the answer is "both"! It means I get
to make walking mini-sumo robots! Though hitting the 500g
limit with three or more servos per leg is pushing it...