DC-motor operating point calculator

Linear DC motor steady-state torque/speed line using supplied stall/free-speed data.

motors-dc-motor.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

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

Scenario	speedrpm	powerW
	4800	100.531
	4500	94.2478

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.

below stall0.20 N*m✓ passes

BASELINE INPUTS

stallTorque1 N*mfreeSpeed6000 rpmloadTorque0.2 N*m

CALCULATED

speed4800 rpm

power100.53 W

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# DC-motor operating point
# Scope: Linear DC motor steady-state torque/speed line using supplied stall/free-speed data.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

stallTorque = 1 N*m
freeSpeed = 6000 rpm
loadTorque = 0.2 N*m

speed := freeSpeed*(1-loadTorque/stallTorque) [rpm]
power := loadTorque*speed [W]

check below stall: loadTorque < stallTorque

scenario alternative: stallTorque = 0.8 N*m

Calculated from your source · not saved

Baseline · Baseline

below stall0.20 N*m ✓ passes

alternative · alternative

below stall0.20 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.

speed: speed = freeSpeed*(1-loadTorque/stallTorque) [rpm]
power: power = loadTorque*speed [W]

Original worked example

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

Given

stall torque: 1 N*m
free speed: 6000 rpm
load torque: 0.2 N*m

Calculated

speed: 4800 rpm
power: 100.531 W

Assumptions and limits

Linear DC motor steady-state torque/speed line using supplied stall/free-speed data.

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: DC-motor operating point. Inputs: voltage; resistance; torque constant; load. Outputs: speed; current; mechanical power. 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: voltage, resistance, torque constant, load
Outputs: speed, current, mechanical power
Modes: calculate, compare, sweep
Drawing: Torque-speed and duty plots

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