Page 376 - Robot Builder's Bonanza

BUILD A FUNCTIONAL REVOLUTE COORDINATE ARM 345

Figure 28- 6 The completed wrist
mechanism provides 3 degrees of freedom. It
can be constructed using ordinary plastic or
wood parts, and three R/C servo motors.

6. Attach the wrist rotator and the wrist flexor/extender subassemblies using two #6 x
3/4″ self- tapping screws. The screws are flat- head and should be tightened so that they
are fairly flush with the surface of the mount.

The completed wrist is shown in Figure 28- 6. When controlling the servos via a microcon-
troller or other means, be careful to limit the movement to the mechanical extents of the pieces.
For the most part, wrists don’t have massive extents of movement— a little goes a long way.

Build a Functional Revolute Coordinate Arm

You can build your own revolute coordinate robotic arm with about $20 in parts— not includ-
ing servo motors. The size of the arm is scalable; the prototype shown in Figure 28- 7 stands
about 8″ tall and has a reach (without gripper) of over 9- 1/2″. It provides 4 degrees of free-
dom, including a rotating base and shoulder, elbow, and wrist joints.

Figure 28- 7 Completed robotic revolute
coordinate arm. Attach the arm to a base or robot
and add a gripper mechanism.

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