CALCULATORS / GEARS AND GEAR TRAINS

Planet spacing and assembly feasibility calculator

Equal planet spacing: assembly phase integer and pitch-circle clearance.

gears-planet-spacing.napkin / editable
✓ checks pass
PLANET SPACINGRing 60 teethSun 20 teeth4 planets × 20 teethPlanet centers 56.569 mm · outside Ø 44 mmAssembly phase 20 · must be a whole number

Dashed circles mark pitch geometry. Tooth outlines are schematic, not manufacturing profiles. Labels come from the evaluated .napkin model.

GEARS / TOOTH SCHEMATICSAME SOURCE

Change an input to see the consequences.

planet clearance56.57 mm✓ passes
assembly phase integer0.00 ✓ passes
whole sun0.00 ✓ passes
positive sun20.00 ✓ passes
whole ring0.00 ✓ passes
positive ring60.00 ✓ passes
whole planet0.00 ✓ passes
positive planet20.00 ✓ passes
whole planets0.00 ✓ passes
positive planets4.00 ✓ passes

BASELINE INPUTS

CALCULATED

planet20
phase20
centers56.569 mm
planetOutside44 mm

Edits change the baseline source.

Calculated from your source · not saved
Baseline · Baseline
planet clearance56.57 mm ✓ passes
assembly phase integer0.00 ✓ passes
whole sun0.00 ✓ passes
positive sun20.00 ✓ passes
whole ring0.00 ✓ passes
positive ring60.00 ✓ passes
whole planet0.00 ✓ passes
positive planet20.00 ✓ passes
whole planets0.00 ✓ passes
positive planets4.00 ✓ passes
alternative · alternative
planet clearance53.74 mm ✓ passes
assembly phase integer0.00 ✓ passes
whole sun0.00 ✓ passes
positive sun16.00 ✓ passes
whole ring0.00 ✓ passes
positive ring60.00 ✓ passes
whole planet0.00 ✓ passes
positive planet22.00 ✓ passes
whole planets0.00 ✓ passes
positive planets4.00 ✓ 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.

planet
planet = (ring-sun)/2
phase
phase = (sun+ring)/planets
centers
centers = module*(sun+planet)*sin(pi/planets) [mm]
planet outside
planetOutside = module*(planet+2) [mm]

Original worked example

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

Given

sun
20
ring
60
planets
4
module
2 mm

Calculated

planet
20
phase
20
centers
56.5685 mm
planet outside
44 mm

Assumptions and limits

Equal planet spacing: assembly phase integer and pitch-circle clearance.

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: Planet spacing and assembly feasibility. Inputs: sun, ring, planet teeth; planet count. Outputs: spacing and phasing checks; adjacent clearance. Model scope: Rigid involute-gear kinematics; qualified stress approximations. 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: sun, ring, planet teeth, planet count
  • Outputs: spacing and phasing checks, adjacent clearance
  • Modes: calculate, compare, sweep
  • Drawing: Animated gear assembly

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

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