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
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.
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.
- 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