# Documentation

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# Simple Gear

Represent gear with fixed gear ratio

Gears

## Description

The Simple Gear block represents a gearbox that constrains the two connected driveline axes, base (B) and follower (F), to corotate with a fixed ratio that you specify. You can choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, ωF and ωB have the same sign. If they rotate in opposite directions, ωF and ωB have opposite signs.

### Axis Motion and Constraint

The Simple Gear imposes a single constraint, specified by the fixed gear ratio gFB, on the motions and torques of the two axes:

±gFB = ωBF = τFB

The plus and minus signs refer to the axes corotating in the same or opposite directions.

If the Simple Gear represents two coupled gear wheels, the gear ratio is related to the ratio of the radii r of the gear wheels and the ratio of the number N of teeth on each gear wheel:

gFB = rF/rB = NF/NB

 Warning:   All gear ratios must be strictly positive. If any gear ratio equals 0 or becomes negative at any time, a Simscape™ Driveline™ simulation stops with an error.

## Dialog Box and Parameters

Follower and base rotate in opposite directions

Select to make the follower and base axes rotate in opposite directions. The default is selected.

Follower (F)/Base (B) gear ratio

Fixed ratio gFB of the follower axis to the base axis. The gear ratio must be strictly positive. The default is `2`.

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