Mechanism for coupling independent gear trains and associated printing device

A printer device, comprising:

• a main housing including a print media cassette receiving slot;
• a first drive assembly mounted to the main housing, the first drive assembly including a motor operatively coupled to rotate a drive gear having a rotation axis, wherein the drive gear is mounted such that a location of the rotation axis is movable relative to the main housing;
• a print media cassette removably inserted into the print media cassette receiving slot, wherein the print media cassette includes a second drive assembly having a driven gear that is engaged with the drive gear of the first drive assembly;
• a retaining mechanism including a portion movable between a gear train coupling position and a gear train release position, wherein, in the gear train coupling position, the portion is positioned to hold the drive gear and the driven gear in driving contact with each other by inhibiting movement of the location of the rotation axis of the drive gear, wherein, in the gear train release position, the portion is positioned to allow disengagement of the drive gear and the driven gear;
• wherein the portion includes a locking arm that is moveable between the gear train coupling position and the gear train release position, wherein the locking arm is located externally of the main housing to enable manual movement of the locking arm between the gear train coupling position and the gear train release position while the print media cassette is inserted in the print media cassette receiving slot.