Fig. 1
From: Smart increment borer: a portable device for automated sampling of tree-ring cores
Planetary gear system used for the gearbox. Planetary gear system consists of a sun gear, b planet gears, and c ring gear. When the sun gear rotates clockwise, the planet gears rotate counter-clockwise (white arrows). The ring gear is fixed. The four axes of the planetary gears rotate in clockwise direction at a slower angular velocity than the sun gear (black arrow), generating a larger torque. The gear ratio of the depicted gear system is about 1:5, which can be calculated from the number of teeth in each gear ((11 + 43)/11 = 4.91)