No this isn’t a CD-ROM drive that has been modified to scratch my head but rather a mechanical assembly in a CD-ROM drive that has me scratching my head wondering how it functions. A few weeks ago I ripped apart an old CD-ROM drive to get a DC motor for the VHS Tape Storage Drive, the circuit board was also cut up while testing the CNC machine that was just assembled (yes it was a very productive afterlife for the old drive).Here is the question. The CD-ROM drive had 3 DC motors, one to open the drive door, one to spin the CD and one to move the read head back and forth. We normally see a small stepper or something similar that can provide accurate position moves of the read assembly. In this case the read assembly moves via a rack and pinion drive system powered directly from a DC motor. When there is a CD in the system I can imagine that the drive would be able to get accurate head position information by reading the CD tracks but how could it move with any accuracy? It has me puzzled, if anyone can fill in the blanks I would be real interested to find out what makes this tick. (more…)