Prefect's Pages.. Engineering .. Robotic Arm (Phase I)

Engineering Projects: Robotic Arm (Phase I)

Photograph of Phase I Arm at Worcester Regional Science Fair, held at Worcester Polytechnic Institute. Phase I was, in several ways, a surprise to many people. It was surprising that the initial version was completed in less than a month, and it was even more surprising that it worked. Many thought the idea of attempting to create a computer-controlled robot arm from scratch was crazy for a 14 year old high school freshman. However, encouragement from my advisors, parents and friends, perseverence, and a little bit of luck led to success. This success and the potential for improvements in the design were primary motivators for the work that would follow.

Vital Statistics

Years	Fall 1989 - Spring 1990
Construction Materials	Wood, steel, carpenter's glue, sheetrock screws, hot glue, nylon mason's line, duct tape, erector set parts, miscellaneous plumbing parts, conductive IC foam, lazy susan bearing, toy truck motor, surplus satellite dish rotator motors, surplus small DC gearhead motors
Degrees of Freedom	Three plus grip (rotary base, shoulder, elbow). Semi-spherical work envelope.
Drive Techniques	Winching nylon line around a pulley on DC motors to raise joints. Gravity needed to lower joints. Base used a feed-through style winch with tensioning springs to rotate base on a lazy susan bearing.
Feedback	Three potentiometers (one per degree of freedom). Limit switch on base rotary motion.
Control Computer	Atari 800XL and Atari 130XE used at different stages of development. At one point an Atari 800XL had been re-packaged into a home-made wooden tower case. Atari 1050 and XF551 floppy drives and ICD SpartaDOS X were used during development.
Interface	Bidirectional joystick ports for digital I/O, paddle controller inputs for analog-to-digital (ADC). The first version of the interface box was constructed in a discarded small DEC case. It was a mess of wires and PC boards. It used reed relays directly driven from the digital I/O lines of the Atari to drive larger relays, which drove the motors. The final revision of the external box improved wiring and reliability considerably, using transistors driving relays for motor control.
Software	Written entirely in Turbo BASIC XL on the Atari 8-bit, using both MyDOS 4.5 and SpartaDOS X (later versions). Provided simple automated tasks via subroutines (no structured arm task language). Several diagnostics tools also written.
Capabilities	Pre-programmed pick-and-place operations with mediocre repeatability, manual operation via joystick.

Video

[Low Quality MPEG1 320x240, 5.8MB]

[High Quality MPEG1 640x480 8.4MB]

Additional Photos


This shot shows the Phase I arm gripper holding a wooden block. Note the ill-fated dual motor design of the gripper. The Phase I arm was entirely dismantled and an entirely new arm was constructed for Phase II (several pieces were saved such as the rounded shoulder supports, motors, etc.)	The Phase Ic interface box sitting atop an Atari XF551 floppy drive.	An Atari 800XL computer repackaged into a tower case, complete with external keyboard.

Software Screenshots


RACS 1.x software intro	RACS 1.x menu example

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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