Load and drum
- Load lifted by the winch
- Diameter of winch drum
- Steady lifting speed
- Target acceleration up to speed
Mechanical · worked example · 4 pages
Geared motor driving a winch
Sizing the electric motor of a winch that lifts a load through a single gear stage: the torque to accelerate the load and both shafts, the steady lifting power, and a check against a candidate motor. Based on example 12.2 from Design Engineer's Handbook (Richards, K.).
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What this calculation covers
Machine and gearing
- Mass of motor shaft assembly
- Motor shaft radius of gyration
- Mass of drum shaft assembly
- Drum shaft radius of gyration
- Number of teeth on the motor gear
- Number of teeth on the drum gear
- Gear stage efficiency
- Gear ratio (drum rev per motor rev)
Lifting force and drum torque
Two demands to keep apart: holding-and-lifting at constant speed takes gravity only; getting up to speed briefly adds the acceleration force on top.
- Standard gravity (from the constants sheet)
- Steady force to lift the load
- Steady torque at the winch drum
- Force while accelerating the load
- Drum torque while accelerating
Referred inertia and motor torque
- Motor shaft inertia
- Drum shaft inertia
- Equivalent inertia at the motor
- Motor angular acceleration
- Torque to accelerate the inertias
- Steady motor torque (gravity only)
- Peak motor torque while accelerating
Speed and power
- Motor speed at the lifting speed
- Motor speed in revolutions per minute
- Steady lifting power at the motor
Motor capacity check
- Candidate motor rated torque
- Candidate motor rated power
- Peak torque within the motor rating
- Steady power within the motor rating
- Torque utilisation (peak)
Comparing a second gear ratio
Peak torque as a reusable function of the ratio (steady power is ratio-independent).
- Peak motor torque for a ratio n
- The chosen 10:1 ratio
- An 8:1 alternative (N_h = 160)
Results summary
- Steady lifting at 0.5 m/s (127 rpm at the motor) is a gravity-only demand: about 409 N·m and 5.45 kW. Getting up to speed briefly needs about 450 N·m of peak torque. The 500 N·m / 5.5 kW candidate passes both checks — 90% of its torque at the peak, 99% of its power steadily; the 8:1 alternative peaks near 553 N·m and fails the torque rating.
Try changing…
- Halve a_req — T_req falls toward the steady 409 N·m; T_ss and P_ss do not move.
- Raise v_L to 0.6 m/s — steady power grows in proportion and fails the 5.5 kW rating.
- Set the efficiency to 100% — referred inertia and steady torque both drop a tenth.