A control knob adjusts linear speed onthe-fly without changing motor speed or reducing gears. Mechanical control of speed and travel direction eliminates the need for electronics and programming. Designed for a PCB measurement/cleaning process, the platform can also be used for bar-code scanners and other applications needing repetitive back-and-forth movement. Backlash-free motion is the result of the rolling-ring bearings inside the drive, which have been specially machined and compressed against the shaft for zero play.