RcTek : Information & Resources for the Model Car Racer

Planetary Geared Differential - Parts Identification

This section of the RcTek site is devoted to differentials, what they are, what they do and the different types of that can be fitted to radio controlled model cars.

This particular article aims to inform the model car owner about the internal parts of a basic planetary geared differential.

Basic Geared Differentials

SVM assembled differential

There are a few different types of geared differentials but they fall into two distinct categories. The bevel geared planetary type differential is featured in this article and the example used is from an SVM Columbia (no longer in production) large scale car made by Radiosistemi. The other type of geared differential uses straight cut gears and works using the same principle. Geared differentials are normally very reliable and durable assemblies and some owners may never feel the need to open them up for maintenance.

Parts Identification

SVM differential exploded view Planet Gear Planet Gear Sun Gear Shim Shim Shim Output Cup Bearing Differential Case Sealing Gasket Ring Gear Pivot Pin Sun Gear Shim Sealing Gasket Differential Case Bearing Output Cup


To serve as a reference for the other articles in the differential section of this site we have an exploded diagram of the SVM differential shown in the illustration.

If you place the mouse pointer over the various parts, the name and a description will appear of that particular part.

Parts Descriptions

The bearings support the differential assembly so that it can rotate freely.
Differential Cases
The casings hold all the internal parts, provide a mounting point for the ring gear and bearings.
Output Cups
The output cups are the part that connect the internal parts of the differential to the driveshafts and are splined or otherwise keyed so that they can be driven by the sun gears.
Pivot Pin
The pivot pin is held in slots in the differential casing and acts as a pivoting/mounting point for the planetary gears.
Planet Gears
The planet gears are not keyed and are free to rotate on the pivot pin. These are sometimes referred to as spider gears.
Ring Gear
This gear is the one that the engine drives via the layshaft. The SVM uses a chain drive, but other cars use either a drive belt or direct gear drive system.
Sealing Gaskets
The sealing gaskets stop the grease from escaping that is used to lubricate or stiffen the action of the differential.
The shims are used to alter the mesh (how close they are together) of the gears. Too little clearance can lead to seizing of the differential due to heat expansion of the gears. Too much clearance can lead to failure of the differential due to the gears becoming damaged.
Sun Gears
The sun gears are splined or otherwise keyed so they can transfer drive the output cups.

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© 2001, 2009 by Darren Burnhill