In a planetary gearbox, many teeth are engaged at once, which allows high speed reduction to be achieved with relatively small gears and lower inertia reflected back to the motor. Having multiple teeth share the load also allows planetary gears to transmit high levels of torque. The combination of compact size, large speed reduction and high torque transmission makes planetary gearboxes a popular choice for space-constrained applications.
But planetary gearboxes do have some disadvantages. Their complexity in design and manufacturing tends to make them a more expensive solution than other gearbox types. And precision manufacturing is extremely important for these gearboxes. If one planetary gear is positioned closer to the sun gear than the others, imbalances in the planetary gears can occur, leading to premature wear and failure. Also, the compact footprint of planetary gears makes heat dissipation more difficult, so applications that run at very high speed or experience continuous operation may require cooling.
When using a “standard” (i.e. inline) planetary gearbox, the motor and the driven equipment must be inline with each other, although manufacturers offer right-angle designs that incorporate other gear sets (often bevel gears with helical teeth) to provide an offset between the input and output.
Input power (max)27 kW (36 hp)
Input speed (max)2800 rpm2
Output torque (intermittent)12,880 Nm(9,500 lb-ft)
Output torque (continuous)8,135 Nm (6,000 lb-ft)
1 Actual ratio is dependent on the drive configuration.
2 Max input speed related to ratio and max output speed
3 Max radial load placed at optimum load position
4 Weight varies with configuration and ratio selected
5 Requires tapered roller planet bearings (not available with all ratios)
Approximate dry weight100 -181 kg (220 - 400 lb)4
Radial load (max)14,287kg (31,500 lb)3
Drive typeSpeed reducer
Hydraulic motor inputSAE C or D hydraulic