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Engineering Projects: Robotic Arm (Phase IIIc)
  [Phase IIIc arm]

Phase IIIc arm removed from the table. The Phase IIIc arm was designed and built within a few weeks between the regional fair held at Worcester Polytechnic Institute and the state fair held at MIT. Because of this unplanned upgrade, I regrettably missed the opportunity to compete in Boston to go to the international science fair in Puerto Rico.

Vital Statistics

Years February 1992 - May 1992
Construction Materials Aluminum, nylon mason's line, threaded rod, bearings, surplus satellite dish rotator motors, misc. surplus motors, misc. plumbing parts, IC foam, etc.
Degrees of Freedom Three plus grip (linear base, shoulder, elbow). Cartesian (box) work envelope. Fourth DOF (pitch wrist) removed from Phase IIIa/IIIb when arm reconstructed out of aluminum.
Drive Techniques Winching nylon lines around a pulleys on DC gear motors to raise joints. Gravity needed to lower joints. Base used a feed-through style winch with tensioning turnbuckle. Wrist pitch motion accomplished via chain drive with 1:1 drive.
Feedback Three potentiometers (shoulder, elbow, wrist). Optical interrupter sensor for linear encoder (base). Optical limit switches on base and for fully open/fully closed on the gripper. Rudimentary analog pressure sensors on gripper pads using conductive IC foam. Photoreflective sensor on gripper to detect presence of objects.
Control Computer Same as Phase IIIa.
Interface Same as Phase IIIa.
Software Same as Phase IIIa.
Capabilities Same as Phase IIIa except for removal of wrist capability.

Additional Photos

[Phase IIIc arm closeup] [Phase IIIc arm] [Phase IIIc gripper]
Phase IIIc arm, showing elbow motor, shoulder motor, and base motor. While the arm retained a similar design to the wood arms from previous phases, several improvements to the design were made. The Phase IIIc arm, side view. The Phase IIIc gripper, the design of which was very much like the Phase IIIa/IIIb gripper. At the very tip of the left side, a homebrew pressure sensor made out of conductive foam can be seen. Also, a photoreflective sensor is mounted near the pressure sensor. This didn't work as well as was hoped and was replaced with tactile switches in Phase IV.
Table of Contents
Robotics Home
Phase I 1989-1990
Phase II 1990-1991
Phase IIIa 1991-1992
Phase IIIc 1992
Phase IV 1992-1993
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