Transmission

8-speed planetary automatic

A cutaway 8-speed automatic transmission with four helical planetary sets and five shift elements, every tooth an exact involute. It reproduces all nine published gear ratios and runs a 3rd-to-4th shift as a mechanism.

Part documents: 34
Mechanisms: 10
Joints: 649
Ratios reproduced to: 6.5e-14

Part Design Surface Design Assembly Kinematics Rendering

The cutaway 8-speed planetary automatic transmission rendered photoreal in the Rendering workbench: a bead-blasted aluminium case with bright machined cut faces opens onto ground-steel helical planet gears, bronze thrust washers and copper-coloured clutch packs, on a glossy dark floor under soft studio light. — 8-speed planetary automatic, cutaway — path traced

The model

What’s included

Gear train

Four helical planetary sets, four planets each — 16 planets
12 external and 4 internal tooth bands at a 20° helix angle
Shafts, bearings and thrust washers

Shift elements

Two brakes and three clutches with their plate packs and drums

Housing

A ribbed, bossed main case with a quarter cut for the cutaway
Bell housing and torque converter envelope
22 quarter-section part variants for the presentation assembly

Assemblies & kinematics

A kinematic assembly, a cutaway presentation assembly and a copy posed mid-shift
One mechanism per gear — nine in all — plus a 3rd-to-4th shift
184 features, each checked against a volume predicted in advance
A 541-pair clearance audit and a clash sweep over the shift

How it was made

The techniques that stand out

Built headlessly by an LLM driving VulkanForge’s MCP server — no UI involved. Before modelling anything it searched the possible layouts, proved the obvious in-line one cannot be built, and modelled one that can.

Exact helical involute teeth

Each tooth follows the true involute to within 2.3e-5 mm and is swept along an exact helix. Tooth-band volumes match the closed-form value to 3.2e-9.

Part Design · Rib along a Helix

Ring gears cut from a solid blank

The four internal ring gears are slotted through solid blanks and land within 7e-7 of the formula volume.

Part Design · Rib + Pocket

Planetary sets as true mechanisms

Every mesh is a gear coupling between two joints on the carrier, so the planetary speed relation holds to 1.7e-15 — the gearbox is solved, not animated.

Kinematics · Gear Joint

One mechanism per gear

The nine gear mechanisms differ only in which three shift elements are locked, and every ratio matches its published fraction — first gear is exactly 108/23.

Kinematics · Rigid joints, Commands

A shift you can check

During the 3rd-to-4th shift the clutch that should hold slips −7.6e-10°, and the one taking over −1.6e-9°: the shift logic is verifiably right.

Kinematics · Command, Mechanism Analysis

Clash-free, measured

Zero clashes over the shift, again with all 16 planets at mid-shift; mesh clearances of 0.082–0.089 mm against a designed backlash of 0.0889 mm.

Kinematics · Clash

Path-traced close-up inside the cutaway transmission: helical planet gears in ground steel with bronze thrust washers, stacked friction and steel clutch plates and machined drums, with shallow depth of field. — Helical planetary sets and clutch packs

The transmission posed mid-shift in the Kinematics workbench: the spec tree lists housing, rotating members, planet gears, shift elements and the gear mechanisms, while the rotating drums and planets are shown turned to the shift pose. — Mid-shift in the Kinematics workbench

Simplified on purpose

Clutch plates are plain rings; packs, bearings and the converter are static.
The torque converter is an outer envelope; pump, valve body, parking pawl and seals are not modelled.
The layout is the one the search found, not a manufacturer’s production arrangement.