Planetary Speed Reducer Selection: Sizing a P Series Unit

A planetary speed reducer is the unit to specify when a drive turns slowly and pulls hard: our P series delivers up to 2,600,000 N·m at output speeds of 0.19 to 60 r/min, from motors of 0.4 to 1,293 kW, in sizes 9 to 36. It earns that rating by splitting the power across several planet wheels through involute planetary gearing that uses both internal and external meshing, so the housing stays light and small for the torque it carries. This guide covers what the series is for, the four decisions its type designation forces, and the three checks that get skipped. Which family of gear unit you need in the first place is a separate question, and the gear reducer selection guide answers it.

Key definitions

• Planetary gearing: a sun wheel driving planet wheels carried on pin shafts in a planet carrier, meshing against a ring gear. The load is shared between planets rather than carried on one tooth pair.
• Power splitting: the reason the unit is compact. Several meshes carry the torque at once, so the same rating fits a smaller housing than a single gear train would need.
• Stage: one sun-planet-ring set. Our units are built with two (YFP2) or three (YFP3) planetary stages.
• Structure: what sits in front of the planetary stages — N for the standard in-line unit, L for an added bevel gear stage, S for a helical gear stage, K for a bevel-helical stage.
• Nominal ratio: the catalogue ratio printed in the tables, which is not always the ratio you calculated; the selection method checks the difference.
• Thermal capacity PG1: the continuous power the unit can carry without auxiliary cooling, published separately for each installation environment.
• Add-on piece: a numbered accessory in the designation — bell housing, motor bracket, swing base, torque arm, base frame — ordered with the unit rather than fitted later.

Where the P series starts and the geared-motor series stop

Series	Transmission	Sizes / frames	Motor or input power	Output speed	Max output torque
R	coaxial helical	13 (R17–R167)	0.12–160 kW	—	17,700 N·m
K	right-angle helical-bevel	12 (K37–K187)	0.18–200 kW	—	49,400 N·m
H/B	modular helical or bevel-helical, 1–4 stages	22 (1–22)	2.52–5,366 kW	1.7–1,200 r/min	470,000 N·m
ZDY / DBY	cylindrical and bevel-cylindrical, hardened teeth	ZDY 80–560, ZLY 112–710	nominal input to approx. 6,666 kW in the ZDY table	—	—
P	2- or 3-stage planetary with power splitting	9–36	0.4–1,293 kW	0.19–60 r/min	2,600,000 N·m

Read the output-speed column before the torque column. The P series is the only series in our range with a published output-speed ceiling of 60 r/min, and that is the real selection boundary. A drive that has to turn a kiln, a mill, a bucket wheel or a winch at a few revolutions a minute needs a ratio that a single coaxial or right-angle unit cannot reach, long before torque becomes the argument. Conversely, a drive at 100 r/min and 300,000 N·m is an H/B series question, not a planetary one — and the two sit side by side in our industrial gear reducer series overview.

Note also what is not in the P row: it is not offered as a geared motor. The catalogue specifies it by the motor power that drives it, and the motor arrives through a named add-on piece. If you want the motor and the gear unit to be one flanged assembly with one nameplate, that is the R, F, K and S range, and the trade-off is set out in our geared motor guide.

Reading the type designation

The printed pattern is YFP2 S AZ -12 -80 -B512 -96 -CW, and every field is a decision:

Field	In the example	What it fixes
Series and stages	YFP2	two planetary stages; YFP3 for three
Structure	S	added helical input stage; N standard in-line, L bevel, K bevel-helical
Output shaft	AZ	hollow shaft with shrink disk; AH hollow with involute splines, BS solid with parallel key, BH solid with splines
Size	12	one of sizes 9 to 36
Nominal ratio	80	the catalogue ratio, not the calculated one
Mounting position	B512	horizontal group B500–B556; vertical V100–V130 shaft down, V300–V330 shaft up
Add-on piece	96	gear housing base; 99 none, 70 input bell housing, 71/72 motor bracket, 73 motor swing base, 74 output bell housing, 75/76 torque reaction arm one side / both sides, 77 torsion shaft support
Input rotation	CW	clockwise; CCW counter-clockwise

Four of those fields are worth dwelling on because they cannot be changed on site.

1. Stages and structure decide the input direction. The standard N structure is in-line: the input shaft is on the same axis as the output. Adding a bevel stage (L), a helical stage (S) or a bevel-helical stage (K) gives a right-angle or offset input, which is usually a question about where the motor fits rather than about the gearing. Decide it from the layout drawing, not after the unit arrives.
2. The output shaft decides whether you need a coupling at all. AZ, the hollow shaft with shrink disk, mounts the unit directly onto the driven shaft and removes the coupling, the base frame and the alignment job — at the cost of needing a torque reaction arm (75 or 76) to hold the housing. BS, the solid shaft with a parallel key, is the conventional foot-mounted answer.
3. The mounting position is also a lubrication decision. Dip lubrication is standard and forced lubrication is available on request, but a motor-driven oil pump is required for the larger vertical mounting arrangements. A unit ordered as V100 or V300 is therefore a different scope of supply from the same unit ordered as B500, and that cost belongs in the comparison. The wider point that mounting position sets the oil fill and the position of the breather and oil plug applies to every series and is covered in our gear reducer maintenance guide.
4. The add-on pieces are the order line, not an afterthought. Because the P series is not a geared motor, the bell housing, bracket or swing base that carries your motor is a numbered item in the designation. So is the base frame (96) and so are the torque arms. A quotation without those numbers is not a complete drive.

The three checks that get skipped

The catalogue's selection pages run six steps: transmission ratio, nominal power against the service factors, peak torque, permissible radial force, actual ratio, and thermal balance. The first two are always done. These three usually are not.

Thermal balance, where the room changes the rating. The two-stage in-line thermal capacity PG1 is published three times over, by installation environment:

Installation environment	Thermal capacity PG1, sizes 9–36
Small confined spaces	21–437 kW
Large halls	29–619 kW
In the open	39–838 kW

The same unit in a closed pit carries roughly half the continuous power it carries outdoors. That makes the installation environment a selection input, not site information — and it is the figure most often missing from an enquiry.

Actual ratio. The nominal ratios in the two-stage in-line table are 25, 28, 31.5, 35.5 and 40 at input speeds of 750, 1,000 and 1,500 r/min, and three-stage units reach far higher; our data publishes no single ratio range for the series, so the ratio comes from the table for the structure and size you are in. The catalogue's own worked example is the lesson: a 75 kW belt conveyor drive at 1,500 r/min calculates a required ratio of 227 and the unit selected is YFP3N-AZ-17-225-B500-96 — a nominal 225. The output speed you actually get is not the one you asked for, and whether the difference matters is a process question only you can answer.

Peak torque and radial force. The continuous rating is not the whole duty. A drive that starts against a loaded conveyor, reverses, or takes a shock load has a peak the frame must survive, and an overhung load on the output shaft has to be inside the permissible radial force for that size. Both are table look-ups and both are ours to do — send the duty and we will run them.

Sizing a P series unit, step by step

1. State the output speed and the output torque, or the absorbed power and the speed. Below 60 r/min, this series is in scope.
2. Calculate the ratio from your input speed. The tables are built around 750, 1,000 and 1,500 r/min inputs.
3. Apply the service factors to the required power and compare against the nominal power rating for the size, structure and ratio. The published two-stage in-line ratings run from about 13 kW (size 9, ratio 40, 750 r/min) to about 12,934 kW (size 36, ratio 31.5, 1,500 r/min) as printed.
4. Check peak torque against the duty: starts per hour, load character, reversals.
5. Check permissible radial force if anything hangs on the output shaft.
6. Take the actual nominal ratio from the table and confirm the resulting output speed is acceptable.
7. Check thermal balance for your installation environment, and add forced lubrication or an oil pump if the position demands it.
8. Fix the geometry and the scope: structure, output shaft, mounting position, add-on pieces, input rotation.

Our recommendation

Specify the P series when the output speed is below 60 r/min or when the torque is beyond the 49,400 N·m that our largest right-angle geared-motor unit carries. Choose AZ with a torque arm where the unit can sit on the driven shaft and BS where it cannot. Treat the mounting position as part of the lubrication scope, treat the installation environment as a rating input, and put the add-on piece numbers on the order line, because this series is supplied as a gear unit with a mounting arrangement rather than as a geared motor. Where the duty is fast rather than slow, the comparison is the H/B series, and where it is a belt conveyor specifically, start from our conveyor gearbox selection guide.

Send the output speed, the output torque or absorbed power, the input speed, the load character, the starts per hour, any overhung load, the installation environment and the mounting arrangement through the enquiry form. Our Reducer Sales department and engineers return a size, a complete type designation, the nominal power and permissible torque against it, the thermal rating for your environment and a dimension drawing; the P series catalogue and every other series catalogue are on the gear reducers pages. Yanfeng Group Co., Ltd. has designed and built reducers and plastic weaving machinery in Pingyang, Wenzhou since 1987, and these units are used in metallurgy, mining, hoisting and transport, electrical power, energy resources, construction and building materials, light industry and traffic. Office hours are Monday to Saturday 08:00–17:30 and Sunday 09:00–17:30, China Standard Time (UTC+8).