Just like their real-life counterparts, LEGO transmissions are mechanisms capable of changing their internal gear ratio. They can increase gear reduction in the drivetrain when more torque is needed and decrease it when speed is of greater importance. It’s the same principle at play when shifting gears in a car or in a bicycle, and this ability makes LEGO electric motors much more versatile.

A typical transmission has a number of fixed gear ratios, one of which can be selected at a time. Such a gear ratio is often simply called a speed or a gear: We can shift to lower gear (increasing the gear reduction) or to higher gear (decreasing the gear reduction). Therefore, a transmission must have at least 2 gears (as shown in Figure ...

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