Transmission

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The transmission uses the power created by the engine or the electric motor to put the RC vehicle into motion. It is a collection of components that moves the power from the engine to the wheels. The transmission system is mounted onto the chassis of a vehicle and in RC cars can include one or several differentials.

Transmission systems for RC cars widely differ between engine based cars (nitro or gas) and electric powered vehicles.

The different components of the transmission system

Transmission systems vary greatly from simple rear-wheel drive to complex four-wheel drive cars. In any case, the understanding and the smooth operation of the transmission and its parts is paramount to the efficiency of the car.

Majot components of a 4WD RC transmission system
Components of a 4WD RC transmission

The transmission system of a simple two-wheel drive RC car is basically shafts and gears. In more advanced systems or in four-wheel drive cars, there might be one or up to three differentials and in order to understand how an RC transmission works, it is important to understand what a differential is and how it works.

Understanding a differential

The differential is a system that allows the drive wheels to turn at different speeds, which is required when any car is negotiating a turn. In a turn, the outside wheel must travel farther, which means it must travel faster than the inside wheels. If a car had no diffential, when turning, one set of wheels on one side of the car would skid and create an important resistance and torque in the wheels axle(s) in the long run possibly damaging the axle(s).

View of the internal and external parts of a differential
View of the parts of a differential

Cars with four-wheel-drive (4WD) have several differentials to perform the same task as a two-wheel-drive (2WD) differential, sometines adding a third and central differential to distribute the power load between the rear and the front wheels.

There are different types of differentials such as gear differentials or ball differentials.

Differentials should be serviced regularly and such maintenance should include:

  • Inspection and cleaning (both for ball and gear differentials)
  • Replacement of differential bearings or worn gears
  • Changing of the oil and lubricant
  • Inspection of the slipper clutch and adjustment

Modern RC cars use oil-filled differentials. The choice of oil particularly its viscosity will influence the distribution of power between the front and rear wheels and ultimately the car's handling abilities.

For more information on the precise operations of the different types of differentials, their maintenance and the choice of differential oils see the 'Differential' article.

Electric cars transmission systems

Contrary to automobiles or engine RC cars, electric RC cars have a "single speed" transmission system. This is due to the brushed or brushless electric motor they use and which can deliver power instantly to the wheels, even when the car is standing still, making the presence of an advanced or complex transmission system unnecessary.

The transmission system of an electric RC car can range from extremely simple such as in a formula 1 car in which the electric motor is connected to a spur gear which connects the power directly to the wheels, or much more complex such as in the case of four-wheel-drive (4WD) RC cars which can have as much as 3 different differentials.

Complete RC 4WD transmission system
View of a complete RC 4WD transmission system

The transmission system consists of a pinion gear which is plugged onto the motor output shaft. The motor and pinion gear are placed in close promixity of the spur gear to allow the pinion gear when rotating to transfer its rotation to the spur gear. The spur gear can be a standalone gear or mounted on the center differential. In any case, the spur gear will transfer the power to the rear and front axles either directly or through the center differential, the axles will in turn transfer the power to the front and rear differentials which are themselves connected to the wheels through axles.

Some transmission systems will use belts instead of driveshafts. This allows drivers to modify the tension of the belts and alter the behavior of the vehicle accordingly. The downside is that belt driven transmissions will be more susceptible to rocks and small gravels to get caught between the belt and the gears. See the 'Belt transmission' article for more detailed information.

The amount of power transfered from the motor to the wheels will then depend on several factors:

By playing around with gear sizes and oil viscosity, RC drivers are able to adjust the behavior of the car by allowing more power to be transferred to the front or back wheels.

Engine cars transmission systems

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In vehicles that make use of internal combustion engines whether nitro or gas, the transmission system is quite different than in electric models. Engine cars use a multi speed gear system that will take longer to build up the torque required to enforce movement of the wheels while an electric vehicle make use of the full torque instantly.

2-speed gearbox

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3-speed gearbox

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