Motor gearbox selection calculator

Torque/speed after a reduction with supplied efficiency.

motors-gear-reduction.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

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

Scenario	torqueN*m	speedrpm
	4.5	300
	3.6	300

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.

output torque target4.50 N*m✓ passes

BASELINE INPUTS

motorTorque0.5 N*mmotorSpeed3000 rpmratio10 efficiency0.9

CALCULATED

torque4.5 N*m

speed300 rpm

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Motor gearbox selection
# Scope: Torque/speed after a reduction with supplied efficiency.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

motorTorque = 0.5 N*m
motorSpeed = 3000 rpm
ratio = 10
efficiency = 0.9

torque := motorTorque*ratio*efficiency [N*m]
speed := motorSpeed/ratio [rpm]

check output torque target: torque >= 4 N*m

scenario alternative: motorTorque = 0.4 N*m

Calculated from your source · not saved

Baseline · Baseline

output torque target4.50 N*m ✓ passes

alternative · alternative

output torque target3.60 N*m × fails

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 = motorTorque*ratio*efficiency [N*m]
speed: speed = motorSpeed/ratio [rpm]

Original worked example

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

Given

motor torque: 0.5 N*m
motor speed: 3000 rpm
ratio: 10
efficiency: 0.9

Calculated

torque: 4.5 N*m
speed: 300 rpm

Assumptions and limits

Torque/speed after a reduction with supplied 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: Motor gearbox selection. Inputs: motor envelope; desired output torque and speed; efficiency. Outputs: feasible reduction ratios. Model scope: Motor and load parameters with explicit operating limits. 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: motor envelope, desired output torque and speed, efficiency
Outputs: feasible reduction ratios
Modes: calculate, compare, sweep
Drawing: Torque-speed and duty plots

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