A gravity rotary device (20; 60; 80; 90; 100) comprising: - a first disk (21; 61; 81; 101; 118) comprising: - a central axis (AA') about which the disk is capable of turning; and - at least one peripheral axis of rotation (BiBi') arranged at a distance from and parallel to the central axis (AA'); - at least one peripheral rotary shaft (26i; 65i; 85i) arranged at a distance from the central axis (AA') of the first disk (21; 61; 81; 101), and suitable for turning about the peripheral axis of rotation (BiBi'), parallel to the central axis (AA'), and coupled to the first disk (21; 61; 81; 101; 118); and - at least one mass support (27i; 66i; 86i; 91i; 102i; 110i) mounted on the peripheral rotary shaft (26i; 65i; 85i); characterized in that the mass support comprises a mass (Mi) suitable for being moved away from the rotary shaft in order to produce torque causing the rotary shaft and consequently the first disk to pivot and in that the device further comprises: - reduction gearing (30i, 301, 302, 303, 304; 40i; 120i) for reduction from the first disk to the mass support, the gearing being arranged between the peripheral rotary shaft (26i; 65i; 85i) and the first disk (21; 61; 81; 101; 118), the gearing comprising a rotary inlet part (37; 41; 121) connected to the peripheral rotary shaft and a rotary outlet part (33; 51; 127) connected to the first disk, the rotary inlet and outlet parts being on the same axis, the reduction gearing enabling the rotation of the peripheral rotary shaft to be transmitted to the first disk; - means (34, 35i, 35i-1, 35i-2, 36i; 44, 49, 531, 532, 561, 562, 59i, 59i-1, 59i-2, 59i-3; 130, 131, 132) for fastening at least a portion of the reduction gearing in a stationary position in order to prevent it from turning about the peripheral axis of rotation; - a freewheel (28i; 67i) arranged on the peripheral rotary shaft (26i; 65i, 85i); and - means (82, 84, 87, 88; 92, 93, 94, 95, 96, 97; 103i, 104i; 111, 112, 113, 114, 115) for modifying the angle of inclination (a11, a12, a13, a14) of a mass support (86i; 91i; 102i; 110i) on the peripheral rotary shaft (26i; 65i; 85i) relative to the horizontal passing through the peripheral axis of rotation (BiBi') of the shaft. - a first disk (21; 61; 81; 101; 118) comprising: - a central axis (AA') about which the disk is capable of turning; and - at least one peripheral axis of rotation (BiBi') arranged at a distance from and parallel to the central axis (AA'); - at least one peripheral rotary shaft (26i; 65i; 85i) arranged at a distance from the central axis (AA') of the first disk (21; 61; 81; 101), and suitable for turning about the peripheral axis of rotation (BiBi'), parallel to the central axis (AA'), and coupled to the first disk (21; 61; 81; 101; 118); and - at least one mass support (27i; 66i; 86i; 91i; 102i; 110i) mounted on the peripheral rotary shaft (26i; 65i; 85i); - reduction gearing (30i, 301, 302, 303, 304; 40i; 120i) for reduction from the first disk to the mass support, the gearing being arranged between the peripheral rotary shaft (26i; 65i; 85i) and the first disk (21; 61; 81; 101; 118), the gearing comprising a rotary inlet part (37; 41; 121) connected to the peripheral rotary shaft and a rotary outlet part (33; 51; 127) connected to the first disk, the rotary inlet and outlet parts being on the same axis, the reduction gearing enabling the rotation of the peripheral rotary shaft to be transmitted to the first disk; - means (34, 35i, 35i-1, 35i-2, 36i; 44, 49, 531, 532, 561, 562, 59i, 59i-1, 59i-2, 59i-3; 130, 131, 132) for fastening at least a portion of the reduction gearing in a stationary position in order to prevent it from turning about the peripheral axis of rotation; - a freewheel (28i; 67i) arranged on the peripheral rotary shaft (26i; 65i, 85i); and - means (82, 84, 87, 88; 92, 93, 94, 95, 96, 97; 103i, 104i; 111, 112, 113, 114, 115) for modifying the angle of inclination (a11, a12, a13, a14) of a mass support (86i; 91i; 102i; 110i) on the peripheral rotary shaft (26i; 65i; 85i) relative to the horizontal passing through the peripheral axis of rotation (BiBi') of the shaft.