Well, if Servo Writer is a robot, then so's WhizzyWriter.
Here's the motor. This was the X-axis motor from a printer (the one which pulls the print head across the paper). I have attached a disc of white plastic to it as the reflector for the optical position sensor.
This is an aluminuim U section mounted to the motor. Two screws were screwed into section, one on either side of the motor shaft to fix it in position. Note the black line drawn on the "reflector" and the multicoloured wires from the sensor.
This is the PCB. Couldn't be simpler. 5-way edge connector for the In-Circuit Serial Programmer (ICSP), 8 LEDs and 8 resistors. (Oh, and a pic.) I added 2 resistors and the cable for the opto sensor after this photo was taken.
This is the full machine. The motor is just clamped in a laboratory retort stand. (Doesn't everyone have a couple of these?) Note the batteries at the other end for balance.
WhizzyWriter whizzing and writing.
And, of course, just to fulfill the requirements...
Technically and mechanically, this one's complete, and I'm marking it as such, but I'm going to continue to work on the software (posted above). I want to make it scroll a message and do some other fancy tricks.
14-Dec-2008: Final, final, final update (maybe): New video. New software build (containing COMPLETE ASCII 8x8 font with characters 33 through 127).
Oh, yeah. Here are the uppercase and lowercase portions of the font.