Mechanical Design Data and Machine-Element Reference: PRIME MOVERS

Context and scope

Comprehensive Reference for Mechanical Design, Power Transmission, and Machine Element Selection

PRIME MOVERS

Electric Motors — Three-Phase

Overview

This chapter covers the selection, specification, and application of electric motors used in mechanical design. It addresses both three-phase and single-phase motor types, focusing on enclosure protection ratings, mounting configurations, wiring connections, shaft load capacities, and combined load analysis. Understanding these parameters is essential for correctly specifying motors in industrial and commercial applications.

Key Concepts

• Enclosure Protection (IP Ratings) — Standardised codes indicating the degree of protection a motor enclosure provides against solid objects and water ingress
• Mounting Arrangements — The physical orientation and method by which a motor is secured to equipment or a base structure
• Connection Diagrams — Wiring schematics showing how motor terminals are connected for different configurations (e.g., star, delta, multi-speed)
• Maximum Shaft Loads — The permissible radial and axial forces that can be applied to a motor shaft without causing premature bearing failure
• Combined Load Capacity — The relationship between simultaneous radial and axial loading, where increasing one reduces the allowable proportion of the other
• Single-Phase Motor Types — Different capacitor configurations used to achieve varying starting torque and running efficiency characteristics

Totally Enclosed Fan Cooled (TEFC) Three-Phase Motors

• Enclosure type: Totally Enclosed Fan Cooled (TEFC)
• Protection rating: Designed to achieve a high-level dust and water ingress protection rating
• Insulation class: Class 'F' insulation standard
• Power range: Typically available from fractional kilowatt ratings up to several hundred kilowatts
• Frame sizes: Standardised frame designations enabling interchangeability between manufacturers

Degrees of Protection (IP Rating System)

• The IP (Ingress Protection) code uses two numerals to describe protection levels
• First numeral — Protection against contact with live/moving parts and ingress of solid foreign bodies
• Second numeral — Protection against water ingress

IP Rating Breakdown

• IP44 — Protected against solid objects greater than 1 mm and water splashed from any direction
• IP54 — Complete protection against contact with live or moving parts inside the enclosure; water splashed from any direction shall have no harmful effect
• IP55 — Protected against harmful dust deposits; protected against water jets projected by a nozzle from any direction
• IP56 — Dust cannot enter in sufficient quantity to interfere with operation; protected against heavy seas or powerful water jets
• IP65 — Complete protection against dust ingress; protected against water jets from any direction
• IP6X — Dust-excluding, ignition-proof rating

Mounting Arrangements

• Foot Mounting (Horizontal) — Motor secured via feet on the base; most common arrangement
• Flange Mounting — Motor attached via a flange on the drive end for direct coupling
• Face Mounting — Motor secured via a face plate, typically for close-coupled applications
• Foot/Flange Combination — Provides flexibility for both base-mounted and direct-coupled installations
• Foot/Face Combination — Allows either foot or face mounting depending on the application
• Foot Mounting (Vertical) — Used where vertical shaft orientation is required (e.g., pumps)
• Standard designation codes (e.g., B3, B5, B14, V1, V3, V5, V6) identify the specific mounting configuration

Connection Diagrams — Three-Phase Motors

• Star (Y) Connection — Used for standard voltage applications; provides lower starting current
• Delta (Δ) Connection — Used for lower voltage applications; provides higher starting torque
• Star-Delta Starting — A switching method that starts in star (reduced voltage) then transitions to delta (full voltage) to limit inrush current
• Multi-Speed Motors (Dahlander Connection) — Use tapped windings to achieve two operating speeds from a single winding
• Multi-Speed Motors (Separate Windings) — Use two independent windings for two distinct operating speeds with greater flexibility

Maximum Shaft Loads

• Motor bearings are rated for specific maximum radial and maximum axial loads
• Loads are specified per frame size and number of poles
• As frame size increases, both radial and axial load capacities increase proportionally
• Larger pole counts (lower speed motors) within the same frame generally have similar load ratings

Combined Radial and Axial Load Capacity

• When both radial and axial loads are applied simultaneously, neither can reach its individual maximum
• The relationship follows a curved reduction line — as the proportion of one load type increases, the allowable proportion of the other decreases
• Smaller frame sizes have steeper reduction curves (less tolerance for combined loading)
• Larger frame sizes show more gradual curves (greater tolerance for combined loading)
• The combined load chart is used to verify that the actual operating loads fall within the safe operating envelope

Single-Phase Motor Designs

• Manufactured to comply with relevant international standards
• Standard enclosure provides high-level protection against dust and water ingress

Construction

• Stator frames are typically die-cast with integral end-shields and flanges
• Bearings: Ball-type bearings, fitted as standard and packed with grease for life

Insulation and Temperature Rise

• Insulation: Class F rating as standard
• Temperature rise: Class B temperature rise standard
• Operates satisfactorily at ambient temperatures from approximately −30°C to +45°C
• Rated for altitudes up to 1000 metres above sea level

Protection

• Thermal overloads: Manual-reset type, fitted as standard
• Located conveniently in the top-mounted terminal box
• Important: Capacitor-type motors must not be run under no-load conditions (risk of capacitor or winding damage)

Single-Phase Motor Types

• (1) Permanent Capacitor (4APC)

  • Suitable for fans, blowers, and centrifugal pumps
  • Starting torque: 30–50% of full load torque (depending on frame size)
  • Motor started by a permanently connected capacitor

• (2) Capacitor Start / Induction Run (4APJC)

  • Suitable for industrial and agricultural applications requiring higher starting torque
  • Starting torque: 160–230% of full load torque (depending on frame size)
  • Uses a start capacitor with an auxiliary winding
  • Auxiliary winding disconnected by centrifugal switch after start-up

• (3) Capacitor Start / Capacitor Run (4APCC)

  • Offers the highest starting performance, efficiency, and power factor
  • Uses both start and run capacitors permanently connected
  • Allows higher output within a given frame size

Mounting Arrangements (Single-Phase)

• Standard: Foot mounting (B3)
• the practitioner: "C" type face mounting (B14) at the drive end
• Can be supplied with or without feet

IP Protection Rating Summary

Maximum Shaft Loads (Selected Frame Sizes)

Single-Phase Motor Type Comparison

Mermaid Diagrams

IP Rating Selection Flowchart

flowchart TD
    A[Identify Operating Environment] --> B{Dust Exposure?}
    B -->|Minimal| C{Water Exposure?}
    B -->|Moderate - not harmful| D[IP5X First Numeral]
    B -->|Heavy - must exclude| E[IP6X First Numeral]
    C -->|Splashing only| F[IPX4 Second Numeral]
    C -->|Water jets| G[IPX5 Second Numeral]
    C -->|Heavy seas / powerful jets| H[IPX6 Second Numeral]
    D --> I[Combine First + Second Numeral]
    E --> I
    F --> I
    G --> I
    H --> I
    I --> J[Selected IP Rating]

Single-Phase Motor Type Selection

flowchart TD
    A[Single-Phase Motor Required] --> B{Starting Torque Requirement?}
    B -->|Low: 30-50% FLT| C[Permanent Capacitor - 4APC]
    B -->|High: 160-230% FLT| D{Efficiency Priority?}
    D -->|Standard| E[Capacitor Start / Induction Run - 4APJC]
    D -->|High efficiency + power factor| F[Capacitor Start / Capacitor Run - 4APCC]
    C --> G[Fans, Blowers, Centrifugal Pumps]
    E --> H[Industrial, Agricultural, Demanding Starts]
    F --> I[High-Performance Applications]

Motor Mounting Decision Process

flowchart TD
    A[Select Mounting Arrangement] --> B{Shaft Orientation?}
    B -->|Horizontal| C{Coupling Method?}
    B -->|Vertical| D[Vertical Foot Mount - V5/V6]
    C -->|Base mounted - belt/chain drive| E[Foot Mount - B3]
    C -->|Direct coupled - aligned| F{Space Constraint?}
    F -->|Standard| G[Flange Mount - B5]
    F -->|Compact / close-coupled| H[Face Mount - B14]
    C -->|Flexible - both options needed| I[Foot/Flange or Foot/Face Combo]

Combined Load Assessment Process

flowchart TD
    A[Determine Applied Loads] --> B[Identify Frame Size and Pole Count]
    B --> C[Look Up Max Radial Load from Table]
    B --> D[Look Up Max Axial Load from Table]
    C --> E[Calculate Radial Load Proportion]
    D --> F[Calculate Axial Load Proportion]
    E --> G[Plot on Combined Load Chart]
    F --> G
    G --> H{Point Within Envelope?}
    H -->|Yes| I[Motor Selection Acceptable]
    H -->|No| J[Select Larger Frame Size and Re-check]

Key Terms Glossary

• TEFC (Totally Enclosed Fan Cooled) — A motor enclosure type where an external fan provides cooling air over the motor casing, while the internal components are sealed from the environment
• IP Rating (Ingress Protection) — A two-digit classification system indicating the level of protection an enclosure provides against solid objects (first digit) and water (second digit)
• Insulation Class — A rating (e.g., Class B, Class F) defining the maximum temperature a motor's winding insulation can withstand continuously without degradation
• Frame Size — A standardised dimensional designation ensuring physical interchangeability of motors from different manufacturers
• Radial Load — A force applied perpendicular to the motor shaft axis, typically from belt tension, gear mesh forces, or coupled equipment weight
• Axial Load (Thrust Load) — A force applied along the motor shaft axis, typically from fans, pumps, or helical gears
• Star (Y) Connection — A three-phase winding configuration where one end of each winding is connected to a common neutral point; used for higher voltage operation
• Delta (Δ) Connection — A three-phase winding configuration where windings are connected end-to-end in a closed loop; used for lower voltage operation
• Dahlander Connection — A winding arrangement that allows a single set of windings to operate at two different speeds by reconfiguring the pole count
• Centrifugal Switch — A speed-activated switch that disconnects the starting capacitor or auxiliary winding once the motor reaches a set percentage of operating speed
• FLT (Full Load Torque) — The torque produced by a motor at its rated power and rated speed; used as a reference for expressing starting torque percentages

Quick Revision

• TEFC motors are sealed enclosures cooled by an external fan — suitable for dusty/wet environments
• IP ratings use two digits: first = solid protection, second = water protection; higher numbers = more protection
• IP55 is a common industrial standard — dust-protected and jet-water-protected
• IP65 provides complete dust exclusion — required for severe environments
• Mounting codes (B3, B5, B14, V1, etc.) define the physical attachment method and shaft orientation
• Star-delta starting reduces inrush current by starting at reduced voltage (star) then switching to full voltage (delta)
• Dahlander motors achieve two speeds from one winding; separate winding motors offer more speed flexibility
• Shaft loads increase with frame size — always check both radial and axial limits from the data table
• Combined loading reduces individual capacity — use the combined load chart to verify both loads simultaneously
• Single-phase permanent capacitor motors have low starting torque (30–50% FLT) — suitable only for easy-start loads
• Capacitor start/induction run motors provide high starting torque (160–230% FLT) — suitable for demanding applications
• Capacitor start/capacitor run motors offer the best efficiency and power factor — ideal for high-performance needs
• Never run capacitor-type single-phase motors unloaded — risk of damage to capacitors or windings
• Class F insulation with Class B temperature rise is a common conservative rating approach — provides thermal margin
• Standard operating conditions: ambient −30°C to +45°C, altitude up to 1000 m above sea level

Electric Motors — Gears, Motors & Geared Motor Units

Overview

This set of notes covers three interconnected areas of mechanical power transmission and drive system design:

• Geared motor units — pre-engineered combinations of electric motors and gearboxes classified by drive type, including selection tables for output speed, torque, power, and unit sizing
• Spur and helical gears — fundamental gear types used in mechanical power transmission, covering gear geometry, velocity ratios, tooth parameters, module selection, design principles, clearance, and force analysis
• Electric motors — selection and specification of three-phase and single-phase electric motors, including performance data, efficiency characteristics, mounting arrangements, synchronous speeds, overhung load calculations, and a step-by-step motor selection method

Together, these topics form the core knowledge required to design and specify mechanical drive systems from the prime mover (motor) through the transmission (gears/gearbox) to the driven load.

Key Concepts

• Geared motor drive classifications define standard combinations of motor power, gear ratio, output speed, output torque, and unit frame size for pre-engineered gearmotor assemblies
• Velocity ratio (VR) is the fundamental relationship between driver and driven gear, determined by the ratio of teeth or pitch circle diameters
• Module (M) is the key sizing parameter for gear teeth, linking pitch circle diameter to the number of teeth and governing tooth strength
• Hunting teeth ensure even wear distribution by requiring no common factor between the number of teeth in the pinion and wheel
• Gear tooth forces consist of tangential, separating (radial), and (for helical gears) axial components — all of which must be accounted for in shaft and bearing design
• Gear efficiency is typically 95–96% per pair for well-machined, lubricated gears on rolling-element bearings; overall efficiency compounds across multiple stages
• Squirrel cage induction motors are the most common type in engineering applications, self-adjusting to load via changes in current draw and slip
• Motor selection follows a structured method: determine mechanical requirements → choose motor from performance tables → verify speed at design load → check overhung and thrust loads → extract dimensions

Geared Motor Units

Drive Classification System

• Geared motor units are pre-engineered assemblies combining an electric motor with an integrated gearbox
• Units are classified into drive classifications (e.g., Classification 2, 3, 4) which represent different ranges of output capability
• Each classification provides a selection table cross-referencing:
  • Nominal output speed (rev/min) — ranging from approximately 20 to 288 rev/min
  • Nominal gear ratio — typically from 5:1 up to 70:1
  • Motor power (kW) — ranging from 0.12 kW to 4.0 kW (varies by classification)
• For each combination, the table specifies:
  • Output power (kW)
  • Output torque (Nm)
  • Unit frame size (e.g., JPM11, JPM17, JPM22, JPM26, JPM30)

Selection Considerations

• As gear ratio increases, the available motor power range narrows (higher ratios support fewer high-power options)
• As output speed decreases (higher ratio), output torque increases proportionally
• Actual output speeds depend on the full-load speed of the motor and the exact gear ratio, and may differ from nominal speeds listed
• Higher drive classifications generally support higher output torques and powers for equivalent speed ranges
• Frame size increases with increasing power and torque requirements

Geared Motor Dimensions

• Geared motors are available with plug-in and solid output shafts
• Standard mounting is foot mounting (Type 2), with dimensions specified for each frame size
• Key dimensional parameters include:
  • Overall envelope (height, width, length)
  • Shaft dimensions (diameter, keyway, length)
  • Mounting bolt patterns (foot bolt spacing, flange PCD)
  • Centre height and shaft centreline offsets
• Dimensions scale with frame size — larger frames (e.g., JPM30) have significantly larger envelopes and shaft diameters than smaller frames (e.g., JPM11)

Spur and Helical Gears

Types of Gears

• Common gear types in engineering include: spur, helical, double helical (herringbone), bevel, hypoid, and worm
• Two gears in mesh are called a gear pair
  • Mesh is normally external, but may be internal (one gear has teeth cut internally)
  • The smaller gear is the pinion; the larger is the wheel
  • The gear transmitting input torque/power is the driver; the output gear is the driven
• In standard mechanical power transmission, the driver is typically the pinion — the wheel rotates slower, providing speed reduction
• When more than two gears are in continuous mesh, this forms a gear train
  • Simple gear train — gears in series on separate shafts; intermediate gears are called idler gears (they do not change the overall velocity ratio)
  • Compound gear train — multiple gear pairs where intermediate shafts carry both a wheel and a pinion; the overall VR is the product of individual pair VRs
  • Planetary (epicyclic) gear train — compact arrangement with a sun gear, planet gears, and a ring gear

Spur vs Helical Gears

• Spur gears have teeth cut parallel to the shaft axis
• Helical gears have teeth cut at an angle (the helix angle, α) to the shaft axis
  • Typical helix angle: ~20° for single helical, ~30–35° for double helical (herringbone)
  • In a helical gear pair, one helix must be right-hand and the other left-hand
  • Helical gears are inherently stronger than spur gears of the same module, allowing a smaller module selection (one standard size down)
  • Helical gears produce an axial force component not present in spur gears

Velocity Ratio (VR)

• For all gears except worm-and-wheel: VR = number of teeth in wheel ÷ number of teeth in pinion
• For a compound gear train: overall VR = product of individual pair VRs
• For a worm and wheel: VR = number of teeth in wheel ÷ number of starts in worm

• Very high velocity ratios are undesirable due to the large number of teeth needed on the wheel, making accurate machining difficult and requiring large centre distances

Number of Teeth

• It is impractical to have gears with too few teeth (below ~3 teeth causes profile issues)
• Rule of thumb minimums:
  • Spur gears: ≥17 teeth on the pinion
  • Helical gears (20° helix angle): ≥14 teeth on the pinion
• Hunting teeth — for maximum life with meshing gears, it is desirable to distribute wear uniformly among all teeth
  • The ideal condition (all teeth hunting) requires no common factor between the number of teeth in the pinion and the wheel
  • This ensures that the same teeth re-mesh only after the pinion has completed a number of revolutions equal to the number of teeth in the wheel
  • The velocity ratio in this case cannot be reduced to a simpler ratio

• Note: 20/38 and 20/40 have very low cycle repeats (2) because they share a common factor — these combinations lead to uneven wear

Gear Parameters and Geometry

• Pitch Circle Diameter (PCD) — the theoretical circle on which the gear teeth are considered to mesh; denoted as d for pinion and D for wheel
• The relationship between VR and PCD: VR = N/n = D/d (where N = teeth in wheel, n = teeth in pinion)
• Nominal centre distance: C = 0.5 × (d + D) — actual centre distance is usually slightly greater
• Addendum (A) — height of tooth above the PCD line
• Dedendum (B) — height of tooth below the PCD line
• Pressure angle (θ) — angle made by the tangent to the gears at the point of contact; usually 20° (assume unless stated otherwise)
• Pitch point (P) — the point of contact on the PCD; must remain fixed as gears mesh to maintain constant velocity ratio
• Involute profile — the standard tooth profile that keeps the pitch point fixed; can be visualised as the curve traced by unwinding a cord from a cylinder
• For a rack and pinion, the mating profile on the pinion is involute while the rack profile is a straight-sided form at the pressure angle

Clearance

• To minimise friction, teeth should contact only along the front face of the driver and back face of the driven
• Two types of clearance are required:
  • Radial clearance (bottom clearance) — obtained by making dedendum > addendum; usually B = 1.25A
  • Circumferential clearance — very small when gears are new; increases with wear; obtained by making centre distance slightly larger than nominal
• Circumferential clearance causes backlash — the back-and-forth play when one gear is held fixed and the other is rocked

Module (M)

• Module is one of the most important parameters in gear design, defined as: M = d/n = D/N (PCD divided by number of teeth)
• The module must be the same for both pinion and wheel in a gear pair
• Standard modules (first choice, in mm): 1, 1.25, 1.5, 2, 2.5, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 32, 40, 50
• As module increases, tooth size increases → stronger teeth capable of transmitting more torque and power
• Standard proportions based on module:
  • Addendum: A = M
  • Dedendum: B = 1.25 M
  • Tooth depth: A + B = 2.25 M
• Face width (W) rules of thumb based on loading:
  • Light loads: W = 8M
  • Moderate loads: W = 10M
  • Heavy loads: W = 12M
• The face width of the pinion is typically 5–10% larger than the wheel (depending on assembly tolerances)
• Module selection can be done using a module selection chart (log-log plot of power vs pinion speed with module lines)
  • For spur gears with face width = 10M and 18 teeth on pinion
  • Can also be used for face widths 8–12M and pinions with 17–19 teeth
  • Can be used for helical gears with helix angles up to 20° by choosing one standard size smaller module

Gear Design Approach

• A comprehensive gear design procedure references detailed engineering standards with dozens of variables and charts
• The most critical factor: the greater the loading, the larger the module (and therefore the larger the teeth)
• A simplified approach uses the module selection chart to determine appropriate module based on power and pinion speed

Gear Tooth Forces

• Forces act at the pitch point (point of contact on the PCD)
• The resultant transverse force F acts perpendicular to the tooth at the pitch point and represents the total load on the gear shaft at the gear location
• This resultant decomposes into:
  • Tangential force (Fₜ) — the useful force that transmits torque
  • Separating force (Fₛ) — the radial force pushing gears apart along the line of centres; keeps gears in mesh
  • θ is the pressure angle between F and Fₜ (typically 20°)

Spur Gear Forces

• Tangential force: Fₜ = 2T / d
  • Where T = torque (Nm), d = PCD (m)
• Separating force: Fₛ = Fₜ × tan θ
• Resultant transverse force: F = √(Fₜ² + Fₛ²)

Helical Gear Forces

• Tangential force is the same as for spur gears: Fₜ = 2T / d
• Separating force (modified): Fₛ = (Fₜ × tan θ) / cos α
  • Where α is the helix angle
• Axial force (additional): Fₐ = Fₜ × tan α
• Resultant transverse force: F = √(Fₜ² + Fₛ²)
• The resultant transverse force for a helical gear is only slightly larger than for a spur gear, but the axial force is an important additional load that must be carried by the bearings

Worked Examples Summary

Example — Spur Gear Pair Design:

• Given: VR in range 2.5–2.7, pinion teeth = 18, module = 5 mm
• Approach: Tabulate possible wheel teeth (45, 46, 47, 48) and check VR and hunting condition
• Result: 18:47 ratio selected (VR = 2.556, all teeth hunting — no common factors)
• PCD of pinion = 5 × 18 = 90 mm; PCD of wheel = 5 × 47 = 235 mm
• Centre distance = 0.5 × (90 + 235) = 162.5 mm
• Addendum = 5 mm, Dedendum = 6.25 mm, Tooth depth = 11.25 mm
• Face widths (moderate load): Wheel = 50 mm, Pinion = 53.5 mm

Example — Spur Gear Force Calculation:

• Given: PCD = 100 mm, Torque = 800 Nm
• Fₜ = 2 × 800 / 0.1 = 16 kN
• Fₛ = 16 × tan 20° = 5.82 kN
• F = √(16² + 5.82²) = 17 kN

Example — Helical Gear Force Calculation (20° helix angle):

• Fₜ = 16 kN (same as spur)
• Fₛ = (16 × tan 20°) / cos 20° = 6.2 kN
• F = √(16² + 6.2²) = 17.2 kN (only marginally greater than spur)
• Fₐ = 16 × tan 20° = 5.82 kN (additional axial load on bearings)

Electric Motors

Motor Types

• The two most common motor types used in engineering are:
  • Three-phase squirrel cage induction motor — the workhorse of industrial applications
  • Single-phase squirrel cage induction motor — used for domestic and light commercial applications where three-phase supply is unavailable

Three-Phase Motors

• Available configurations include: totally enclosed fan cooled, dust ignition proof, non-sparking, flameproof, two-speed, brake motors, geared motors, and slip ring motors
• The standard off-the-shelf configuration is the totally enclosed fan cooled type with protection designation IP55 or higher
• Data in standard references typically covers sizes from 0.18 to 110 kW (frame sizes 63–280)
• Frame size = distance in mm between the base of the motor feet and the centreline of the rotor — a common designation used by all manufacturers; as frame size increases, motor power increases

Synchronous Speeds (Three-Phase, 50 Hz)

Single-Phase Motors

• Available in three starting methods:
  • Permanent capacitor type
  • Capacitor start / induction run type
  • Capacitor start / capacitor run type
• Three mounting arrangements: standard foot mount, flange mounted, and "C" type face mount
• Only two synchronous speeds available: 2-pole (3000 rev/min) and 4-pole (1500 rev/min)

Motor Operating Characteristics

• Under no-load conditions, the actual motor speed equals the synchronous speed (approximately)
• Full-load speed is less than synchronous speed (the difference is called slip)
• Between no load and full load, the speed-load relationship is very close to linear — linear interpolation can be used for intermediate loads with little error
• Squirrel cage motors self-adjust to load: as load increases, current draw increases to provide the required torque
  • It is poor practice to overload the motor (excess current causes overheating and failure)
  • It is also poor practice to significantly undersize the load relative to motor capacity (motor runs at lower efficiency and wastes space/cost)
• Electric motors, like most prime movers, have lower efficiency at part load than at full load

Performance Data

• Performance tables list for each motor type:
  • Output power (kW), full-load speed (RPM)
  • No-load and full-load current (A), locked rotor current
  • Efficiency at 100% FL, 75% FL, and 50% FL
  • Power factor at 100% FL, 75% FL, and 50% FL
  • Full-load torque (Nm)
  • Starting torque, pull-up torque, maximum torque (multiples of FL torque)
  • Moment of inertia (J), net weight

Motor Mounting Arrangements

• B3 Footmount — standard arrangement with feet for floor mounting
• B5 Flangemount — flange mounted to driven equipment
• B14A / B14B Facemount — face-mounted configuration
• Additional variants exist for combined foot/flange mounting (Type F 160/280 series)
• Dimensions are standardised and tabulated by frame size for all mounting types

Overhung Load and Thrust

• When a gear, pulley, chain-wheel, or flywheel is directly attached to the motor shaft, it creates an overhung (radial) load

• This load must not exceed the motor's allowable value, or bearing life will be reduced

• Overhung load formula:

  F = (2fT) / d = (60fP) / (π × d × N)

  Where:

  • F = overhung load (N)
  • T = motor torque at design load (Nm) — not maximum/full-load torque
  • P = motor power at design load (W) — not maximum/full-load power
  • d = PCD of pulley, sprocket, or gear (m)
  • N = speed at design load (rev/min)
  • f = drive application factor:
    • Chain drive or toothed belt: f = 1.0
    • Gear drive: f = 1.25
    • Vee belt: f = 1.5
    • Flat friction belt: f = 2.0

• If overhung load is excessive, options include:

  • Use a larger pulley or gear (increases d, reducing F)
  • Use a larger motor (higher allowable load)
  • Use an intermediate (lay) shaft with its own bearings coupled to the motor via a flexible coupling — this prevents the overhung load from reaching the motor bearings

Thrust (Axial) Load

• If a mechanism produces a thrust (axial) load on the motor shaft, this must also not exceed the allowable value
• When both radial and axial loads act simultaneously, the allowable thrust load is reduced:
  • If radial load equals maximum allowable → allowable thrust = table value × 0.68
  • If radial load is 50% of maximum → allowable thrust = table value × 0.84

Motor Selection Method (Three-Phase)

1. Determine mechanical requirements — torque, power, and speed
2. Select motor from performance tables — choose a motor at the appropriate synchronous speed with maximum power output (full load) ≥ required design power
   • "Full load" in manufacturer catalogues refers to the maximum continuous load rating
   • The actual load requirement (design power) is often less than maximum
3. Calculate speed at design load — use linear interpolation between no-load (synchronous) speed and full-load speed
4. Check overhung load — if a pulley, gear, or sprocket is directly attached, calculate F and verify it does not exceed allowable values
5. Check thrust load — if applicable, verify axial load is within limits (reducing for combined loading if needed)
6. Extract performance and dimension data — efficiency at design load (interpolated), torque at design load, current draw, shaft diameter, mounting bolt patterns, and overall dimensions

Worked Example — Motor Selection

• Given: Design power = 12 kW at approximately 1450 rev/min, wedge belt pulley (PCD 100 mm, max bore 42 mm) directly on motor shaft
• Step 1: Synchronous speed = 1500 rev/min → 4-pole motor required
• Step 2: Selected motor: frame size 160, 4-pole, maximum output = 15 kW
• Step 3: Speed at design load = 1500 − (12/15) × (1500 − 1455) = 1464 rev/min
• Step 4: Overhung load: F = (60 × 1.5 × 12000) / (π × 0.1 × 1464) = 2348 N → within allowable limit of 2800 N
• Step 5: No axial load in this case
• Step 6: Design load is 80% of full load; efficiency at full load = 88%, at 75% = 87% → efficiency at design load ≈ 87.2%; torque at design load = 78.3 Nm