A timer with teeth
For accurate tracking on an equatorial mount, the larger the diameter of the final gear in the drive chain, the better. However, this would be at odds with the goal of portability. Using a quadrant arm has the advantage of using an apparently large drive gear in a small physical size as only a small part of the perimeter of the ‘complete’ gear is required. In the case of the MiniTrack, the arm represents a section of a gear that would have a diameter of 290mm.
Although quadrant arms have been used in other designs before, what makes this product so unusual is the clockwork motor that drives the arm. The motor used in this design is essentially a one-hour timer installed at one end of the body. It even pings at the end of the run to alert you to the fact that the hour is up. The clockwork motor engages with a series of intermediary gears that ultimately move the quadrant arm via a set of teeth on its curved outer edge.
Quadrant teeth Clockwork motor Quadrant arm