The Robot Arm
| The brain of the Arm is a Betacomputer, developed as a project for the Dutch popular science monthly KIJK. Hans Otten has a very nice page about it on his Retro Computing site. |
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The computer is just a little `controller', a 4" x 3.2" PCB with a 6502 (cpu), a 6532 (RAM, I/O, timer), a 2716 (EPROM) and a 74LS00. The controller plugs into a `terminal', equipped with a keyboard and six LED number displays, used alphanumerically. On the terminal there is also a socket for writing EPROMS, allowing a very cheap setup where you first use the controller to write programs for it. When finished you replace the monitor program with your own EPROM, and then you plug the controller into your hardware project.
The 6532 offers only 128 bytes of RAM. A shocking lack of space, you may think, but the programming language designed for the robot arm is still able to save 40 `steps'. Each of those consists of a single movement - like "rotate 10 degrees left" - and one of three possible speeds for executing the movement. Programming the steps is done by steering the Arm in the desired position using the keyboard (hold down a button, Arm rotates slowly, let go, Arm stops). Press `enter', select the desired speed, done, and so on for the other steps.
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The Arm was made from a large PCB, with a drawing of the parts in copper lines on it. The dark spots are larger copper pads, used for soldering the parts together: a fast and sturdy method of construction. |
The Arm has four degrees of freedom: cant (60 degrees), extend (2.4"), rotate (100 degrees) and open/close the hand. It is powered by four cassette recorder motors. On the shafts of the motors for canting, rotating and extending a vane is mounted. The vane interrupts the lightbeam of an optocoupler. The computer counts the interruptions and derives both position and speed. Counting starts from a reference position, marked by the closing of a microswitch.
