Build Your Own Combat Robot

FIGURE 10-3
Lifting robot
concepts.
Chapter 10: Weapons Systems for Your Robot 211
upcoming section “Launchers”). Pneumatic systems are more complex than electric
linear actuators, having the added bits of tanks, regulators, valves, tubing, and
optional buffer chambers; but in the end, they can make for a weighty and more-flexible
design. A pneumatic-powered lifting arm also has the disadvantage of being
unable to stop in mid-stroke (barring a complex position-controlled feedback system),
which makes it less useful if your tactic is to drag the opponent around the
arena rather than flipping it.
Hydraulics have also been used for lifting arms, but the complexity and weight
of the hydraulic system make this an unlikely option. Unless your robot already
has a hydraulic system onboard for other reasons, an electric linear actuator will
be a much cheaper and lighter weight solution than a hydraulic lifter.
Shaft-driven arms, with the output of a gear or chain reduction directly driving the
arm’s rotation, are a more challenging design for a lifter. Designing a motor drive
capable of supplying, and surviving, the kind of torque needed to lift an opponent
is difficult We’re talking of 500 to 1000 foot-pounds of torque for heavyweights,
here. Most designs of this type use a large-diameter gear or sprocket bolted
straight to the arm as the final drive stage, rather than attempting to drive straight
through a shaft. The advantage of this kind of arm is that the range of rotation
possible is much greater than with a linear actuated arm—often enough to make
the arm able to reach around behind the robot; reach down below it to push it off
obstacles or lift while the robot is upside down; and even, in some cases, travel unrestrained
360 degrees.