The device comprises a shaft 4, a notched mobile memberfor example a wheel 1and at least three arms 2.1, 2.2, 2.3 that together transmit movement between the shaft 4 and the mobile member. Each arm is hinged to two eccentric bearings 3, 3 that hold same parallel to said arm, regardless of the rotational angle of the shaft 4 with which they rotate synchronously. Each arm engages with the notches of the wheel 1 during at least a portion of the cyclic motion of same, by means of at least one tooth 7 of the arm, in such a way as to ensure mutual displacement. The bearings 3, 3 are arranged such that at least one of the arms engages with the mobile member, regardless of the rotational angle of the shaft 4. Said device can be used for producing low-clearance speed reducers.

A developer cartridge may include: a first gear having a small-diameter gear portion and a large-diameter gear portion; and a second gear including: a first columnar portion centered on a second axis; a second columnar portion having a smaller diameter than the first columnar portion; a first engagement portion extending along a portion of a peripheral surface of the first columnar portion and engageable with the small-diameter gear portion; a second engagement portion extending along a portion of a peripheral surface of the second columnar portion and positioned closer to a housing than the first engagement portion in an axial direction and engageable with the large-diameter gear portion; and a protruding portion protruding in the axial direction and rotatable together with the first engagement portion and the second engagement portion. The second engagement portion may engage the large-diameter gear portion after the first engagement portion engages the small-diameter gear portion.

A device having a vibration based propulsion system includes at least one of an extendible and retractable diaphragm, a vibrating mechanism, and an expandable and collapsible body section for driving movement of the device. Some embodiments may also include one or more coverings configured to move to adjust the fluid resistance of the device to improve the efficiency of the device's movement. At least one processor may be connected to at least one of: a transceiver, sensors, a camera, and a drive system for controlling the operations of these mechanisms. A power source may also be attached to these elements of the device to power the device. A remote controller or other computer device may communicate with the device via the transceiver to provide input for steering the device or to receive data collected by the device.

A developer cartridge may include: a first gear having a small-diameter gear portion and a large-diameter gear portion; and a second gear including: a first columnar portion centered on a second axis; a second columnar portion having a smaller diameter than the first columnar portion; a first engagement portion extending along a portion of a peripheral surface of the first columnar portion and engageable with the small-diameter gear portion; a second engagement portion extending along a portion of a peripheral surface of the second columnar portion and positioned closer to a housing than the first engagement portion in an axial direction and engageable with the large-diameter gear portion; and a protruding portion protruding in the axial direction and rotatable together with the first engagement portion and the second engagement portion. The second engagement portion may engage the large-diameter gear portion after the first engagement portion engages the small-diameter gear portion.

A developer cartridge may include: a first gear having a small-diameter gear portion and a large-diameter gear portion; and a second gear including: a first columnar portion centered on a second axis; a second columnar portion having a smaller diameter than the first columnar portion; a first engagement portion extending along a portion of a peripheral surface of the first columnar portion and engageable with the small-diameter gear portion; a second engagement portion extending along a portion of a peripheral surface of the second columnar portion and positioned closer to a housing than the first engagement portion in an axial direction and engageable with the large-diameter gear portion; and a protruding portion protruding in the axial direction and rotatable together with the first engagement portion and the second engagement portion. The second engagement portion may engage the large-diameter gear portion after the first engagement portion engages the small-diameter gear portion.