# Common Gear Constraint

Kinematic constraint for transferring rotational motion at a fixed ratio about parallel axes

## Library

Gears and Couplings/Gears

## Description

This block represents a common gear constraint between two frames, base and follower. The constraint restricts motion, forcing the frames to spin in sync. Each frame, possessing at least one rotational degree of freedom, spins about its individual Z axis.

To assemble, the common gear constraint imposes several restrictions on the relative position and orientation of the port frames. Through blocks such as Rigid Transform, Joints, and Constraints, the remainder of the model must provide the geometric and kinematic relationships to satisfy these restrictions:

• The Z axes of the base and follower frames must point in the same direction.

• The X and Y axes of the base and follower frames, and therefore the frame origins themselves, must lie in the same plane.

The common gear constraint can be internal or external. If the constraint is internal, the base and follower gear shafts spin in the same direction. If it is external, the shafts spin in opposite directions. The tooth ratio between the two gears determines the magnitude of the angular velocity ratio:

$|\frac{{\omega }_{F}}{{\omega }_{B}}|=\frac{{N}_{B}}{{N}_{F}}=\frac{{R}_{B}}{{R}_{F}},$

where:

• ωB and ωF are the angular velocities of the base and follower gears.

• NB and NF are the tooth numbers of the base and follower gears.

• RB and RF are the pitch radii of the base and follower gears. These are the radii of the gear pitch circles, imaginary circles tangent to each other at the tooth-tooth contact point.

Gear Frames and Dimensions

## Dialog Box and Parameters

The block dialog box contains a Properties area with common gear options and parameters.

Type

Select gear type. Options include internal or external. Internal gears have teeth along the inner circumference. External gears have teeth along the outer circumference. The default type is `External`.

Specification Method

Select the method to specify the common gear with. Options include ```Center Distance and Ratio``` and `Pitch Circle Radii`.

### Center Distance and Ratio

Specify the common gear constraint in terms of the center-to-center separation distance and the gear teeth ratio (Nf/Nb).

Center Distance

Enter the center-to-center distance between base and follower gears. Select a physical unit. The default value is ```20.0 cm```.

Gear Ratio

Enter the gear teeth ratio between base and follower gears. This ratio is Nf/Nb, where Nf and Nb represent the number of teeth in the follower and base gears, respectively. The default value is `1.0`.

Specify the common gear in terms of the base and follower gear radii.

Enter the radius of the gear associated with the base frame. Select a physical unit. The default value is `10.0 cm`.

Enter the radius of the gear associated with the follower frame. Select a physical unit. The default value is `10.0 cm`.

## Ports

The block contains frame ports B and F, representing base and follower frames, respectively.