A mechanical speed reducer, in particular for a device for driving at least one wheel of an aircraft landing gear, this reducer including a first sun gear including external toothing, first planet gears meshed with the external toothing of the first sun gear, these first planet gears being carried by a first planet carrier, a stationary ring gear meshed with the planet gears, and second planet gears meshed with a ring gear and with an external toothing of said first planet carrier, these second planet gears being carried by a second planet carrier.

This modular planetary transmission uses a single shared floating carrier to house both input and output planetary gearsets. The input and output sun-gear-shafts are mechanically isolated, and torque is transferred solely through internal gear interactions within the shared carrier. Gear ratios are established by selectively braking one input and one output selector sun-gear-shaft using case-mounted braking elements. Torque flows from the input sun-gear-shaft through the input gearset, rotating the carrier, which in turn drives the output gearset and the output sun-gear-shaft. The resulting input-to-output ratio is defined by the product of the input-to-carrier and carrier-to-output gear ratios. Unique gear ratios are achieved through a two-brake control matrix formed by different combinations of braked selector shafts. The architecture enables fast, full-power shifts without rotating clutches, allows high gear counts, improves packaging efficiency, reduces complexity, and increases durabilitymaking it suitable for high-performance or compact driveline applications.