by Bryan Bergeron
My first robotic arm kit — a six DOF,
all-metal model with high-speed, heavy-
duty servos, and ample power supply —
taught me not to be lulled into the
apparent plug-and-play world of hobby
to the servos, the joints abruptly hyper-extended, flinging a hot soldering iron
against a wall. Then, when I applied
power to the servo controller, the
uncalibrated servo chain contracted,
digging the gripper into the workbench. The unsecured arm flipped onto
its side, knocking over a hot glue gun
in the process. Fortunately, the gun
and iron landed harmlessly on the shop
floor and the arm was undamaged.
Robotics presents a real-word test
of AI, computer vision, and sensor
technologies. Moreover, because
robotics involves physical, as well as
the dangers associated
with building and operating robots extend beyond
keyboard-induced carpal tunnel
syndrome. This is especially true with
the current trend toward heavier,
faster, and more complex robots.
Following is a discussion of robot
design, construction, and operating
practices that can improve the survivability of your robots and minimize the
safety risks to you and bystanders.
Safety should be explicitly
designed into a robot, as opposed to
an add-on made in response to a injury
or robot failure. Appropriate platform
layout, the use of safety subroutines,
as well as physical sensors, intuitive
state indicators, energy management hardware and software, and
kill switches all contribute to a
comprehensive safety design.
In designing a robot platform
layout, the primary goal is to provide a stable support for sensors
and associated electronics within a
structure capable of withstanding
the mechanical stress of motion.
In addition, the platform should
be configured in a way that
protects onboard electronics and
minimizes damage to anything or
anyone unfortunate enough to be hit
by the robot body or effectors.
For example, in designing a
crawler, consider using rubber cushions
to provide hard limits on the range of
leg motion so that the legs don’t clash
into the body while you experiment
with various gaits. This safety precaution can limit damage to the robot
body and servos, and minimize pinch
points that can entangle your fingers.
Similarly, avoid sharp edges and
protruding corners on fast-moving
wheeled robots over a few pounds,
which have a way of colliding with
furniture legs and shins. I have several
robots based on the Traxxas e-Maxx
truck chassis — a popular platform
for robot development. Because the
e-Maxx drive system is capable
of speeds in excess of 30 mph, the
potential for damage to both person
and robot is significant.
If you’re working with a high-speed platform, consider a roll bar and
sturdy frame to protect electronics and
a bumper system that will minimize
damage to human and furniture legs.
I’ve found a pair of calf-high boots
handy when debugging high-speed
robots capable of sudden and unexpected acceleration.
FIGURE 1. Physical tilt sensor based
on mercury switches.
Safety subroutines can be the
easiest safety measures to implement –
if you do your homework in selecting
52 SERVO 01.2007