forward until the brain tells them to stop. It’s an efficient and stable system,
which is why robotics engineers have borrowed it to use in walking robots.
Most passive dynamic walkers are bipeds and walk on two legs. When
they move, they shift all their weight to one leg, and let the other leg swing
forward. Then they shift their weight the other way to allow the other foot
to take a step. (Check out my book BOTS! to see how to make a two-legged
version.)
However, some robotics labs have tried making passive dynamic walkers
with three, four, or even more legs! The extra legs help with balance, but
they also make the pattern of walking much more complicated. When a dog
walks along, it only picks up one foot at a time. A cheetah or a race
horse can trot with two feet always on the ground at the same
time, or gallop with just one foot touching down as it speeds
by. Trying to get a four-legged robot to move in a realistic way
is a big problem scientists are still trying to solve.
One robot dog called Spot, made by Boston Dynamics, has a gait (or
pattern of walking) that’s so real, it’s spooky. Spot’s legs bend the same way
real dog legs bend. And with its sensors and programming, Spot is good at
getting itself back up if it tumbles over on its side. The Walking Robot Dog
you will be making, on the other hand, doesn’t even have knees, so its legs
don’t bend. But it does move one front foot and then the other in a slow,
steady rhythm as it makes its way downhill. It also has a long skinny neck
and a small head, like Spot. The head and tail help keep it balanced. Even
though it isn’t as advanced as Spot, it’s still pretty good at not falling over.
However, there is one engineering challenge you’ll have to solve: The
Walking Paper Robot Dog has no feet. That means it has very little traction
to keep it from sliding downhill. (Think about how the somewhat sticky
rubber on your sneakers, or a dog’s rough paw pads, help the feet grip the
floor.) You may need to find or add a bumpy or sticky texture to your test
ramp, or directly to the ends of your robot’s legs!
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Making Simple Robots, 2nd Edition
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