Winch drum torque and capacity calculator

Constant-radius drum, supplied drivetrain efficiency.

belts-winch.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	torqueN*m	omegarpm	powerW
	7.5	31.831	25
	6	31.831	20

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

motor torque budget7.50 N*m✓ passes

BASELINE INPUTS

load200 Nradius30 mmspeed0.1 m/sefficiency0.8

CALCULATED

torque7.5 N*m

omega31.831 rpm

power25 W

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Winch drum torque and capacity
# Scope: Constant-radius drum, supplied drivetrain efficiency.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

load = 200 N
radius = 30 mm
speed = 0.1 m/s
efficiency = 0.8

torque := load*radius/efficiency [N*m]
omega := speed/radius [rpm]
power := load*speed/efficiency [W]

check motor torque budget: torque <= 10 N*m

scenario alternative: load = 160 N

Calculated from your source · not saved

Baseline · Baseline

motor torque budget7.50 N*m ✓ passes

alternative · alternative

motor torque budget6.00 N*m ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

torque: torque = load*radius/efficiency [N*m]
omega: omega = speed/radius [rpm]
power: power = load*speed/efficiency [W]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

load: 200 N
radius: 30 mm
speed: 0.1 m/s
efficiency: 0.8

Calculated

torque: 7.5 N*m
omega: 31.831 rpm
power: 25 W

Assumptions and limits

Constant-radius drum, supplied drivetrain efficiency.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Winch drum torque and capacity. Inputs: line pull; drum radius; layers; rope diameter. Outputs: drive torque; speed; winding capacity. Model scope: No-slip kinematics with explicit tension and efficiency assumptions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: line pull, drum radius, layers, rope diameter
Outputs: drive torque, speed, winding capacity
Modes: calculate, compare, sweep
Drawing: Animated belt or chain

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS