Page 351 - Robot Builder's Bonanza

320 BUILD ROBOTS WITH LEGS

Figure 27- 1 Bipeds in both android
and humanoid forms.

BIPEDS: ANDROID OR HUMANOID
The terms android and humanoid are used to describe robots that are modeled after the
human form (Figure 27- 1). There’s a head, torso, two legs, and at least one arm. Though
usage varies, the terms don’t mean exactly the same thing. An android is a robot designed to
look as much like a human being as possible, either male, female, or an androgynous mix of
the two (androgyny is where we get the term andr- oid, meaning “like male and female”). The
robot has eyes where we have eyes, a nose, mouth, ears, and other things that make us look
like we do.
Conversely— and somewhat confusingly— a humanoid robot is one that shares the basic
architecture of a human. It has two legs, with a head at the top, and two arms at the side.
Rather than duplicate the appearance of people, it’s meant more to replicate human ability,
such as being able to walk through a hallway meant for humans or sit down in a chair meant
for humans.

NUMBER OF JOINTS/DEGREES OF FREEDOM

Leg motion is provided by a series of joints. Some joints allow the leg to swing back and forth,
while others permit side- to- side motion. The number of joints that provide motion is called the
degrees of freedom, or DOF. For the most part, the more DOF, the more agile the robot. For
amateur robots the 2- and 3- DOF bot designs are more common.
Except for some unique designs that use clever mechanical linkages, each leg DOF needs
a separate motor to control the joint. The more motors, the more expensive the robot; it’s
heavier and larger, too. So consider the number of leg DOF when picking a walking robot
design. That hexapod with 3- DOF legs looks mighty impressive; just remember it needs 18
motors. It’s not unusual for these kinds of robots to cost upward of $600, and that’s before
any microcontrollers or other electronics.

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