In this example, you model a simple pivot mount. This mount
is a compound rigid body with a hexagonal shape and a protruding cylindrical
peg. You represent the hexagonal shape using solid shape ```
Regular
Extrusion
```

. You then offset the protruding peg from the
hexagonal shape using a Rigid Transform block. In later examples,
you use this mount to support mechanical linkages like the double
pendulum and the four bar system.

To model the pivot mount, you use two Solid blocks.
Because the pivot mount has a hexagonal shape, you can model it using
the `Regular Extrusion`

shape. To represent
the cylindrical peg, you use the `Cylinder`

shape.

Each shape has a reference frame with origin at the geometry center. To offset the cylindrical peg with respect to the hexagonal mount, you apply a rigid transform between the two reference frames. You do this using the Rigid Transform block.

The Z axes of the two reference frames align with the cylindrical
and extrusion axes of the peg and mount, respectively. Assuming the
two solids both have thickness *T*, the rigid transform
between the two reference frames is a translation *T* along
the common Z axis.

In later examples, you connect the pivot mount to a binary link
using a revolute joint. One example is a double pendulum that moves
due to gravity. In this example, it helps to rotate the Z axis of
the mount so that it is orthogonal to the world frame Z axis. This
task, which involves a Rigid Transform block, makes the pivot rotation
axis orthogonal to the gravity vector, `[0 0 -9.81] m/s^2`

.

Drag these blocks into a new model.

Block Library Quantity Solid **SimMechanics**>**Second Generation**>**Body Elements**2 Rigid Transform **SimMechanics**>**Second Generation**>**Frames and Transforms**2 Solver Configuration **Simscape**>**Utilities**1 Connect and name the blocks as shown in the figure.

**Note:**Include the disconnected frame line. This line becomes important when you generate a subsystem for the pivot mount. To add this line, right-click on the solid frame line and drag to the right.In the Hexagon block dialog box, specify these parameters.

Parameter Value **Geometry**>**Shape**Select `Regular Extrusion`

.**Geometry**>**Number of Sides**Enter `6`

.**Geometry**>**Outer Radius**Enter `HexagonR`

. Select units of`cm`

.**Geometry**>**Length**Enter `T`

. Select units of`cm`

.**Inertia**>**Density**Enter `Rho`

.**Graphic**>**Color**Enter `HexagonRGB`

.In the Peg block dialog box, specify these parameters.

Parameter Value **Geometry**>**Shape**Select `Cylinder`

**Geometry**>**Radius**Enter `PegR`

. Select units of`cm`

.**Geometry**>**Length**Enter `2*T`

.**Inertia**>**Density**Enter `Rho`

.**Graphic**>**Color**Enter `PegRGB`

.In the To Peg block dialog box, specify these parameters.

Parameter Value **Translation**>**Method**Select `Standard Axis`

.**Translation**>**Axis**Select `+Z`

.**Translation**>**Offset**Enter `3/2*T`

. Select units of`cm`

.In the To World block dialog box, specify these parameters.

Parameter Value **Rotation**>**Method**Select `Standard Axis`

.**Rotation**>**Axis**Select `–Y`

.**Rotation**>**Angle**Enter `90`

.

You can now generate a subsystem to encapsulate the pivot mount
block diagram. The subsystem mask provides a convenient place to initialize
the MATLAB^{®} variables that you defined the block parameters with.
To generate the subsystem:

Select all the blocks excluding Solver Configuration.

Press

**Ctrl+G**to enclose the blocks in a subsystem. Name the subsystem block Pivot Mount.Select the Pivot Mount block and create a subsystem mask, e.g., by pressing

**Ctrl+M**.In the

**Parameters & Dialog**tab of the Mask Editor, drag six edit boxes into the**Parameters**group and specify their properties. Click**OK**.Prompt Name `Hexagon Outer Radius`

`HexagonR`

`Hexagon Thickness`

`T`

`Mass Density`

`Rho`

`Hexagon Color`

`HexagonRGB`

`Peg Radius`

`PegR`

`Peg Color`

`PegRGB`

In the Pivot Mount block dialog box, specify these parameters.

Parameter Value **Hexagon Outer Radius (m):**`4`

**Hexagon Thickness (m):**`0.8`

**Mass Density (kg/m^3):**`2700`

**Hexagon Color [R G B]:**`[0.25 0.4 0.7]`

**Peg Radius (m):**`0.4`

**Peg Color [R G B]:**`[1 0.6 0.25]`

Update the block diagram. You can do this by pressing **Ctrl+D**. Mechanics Explorer opens with a static
display of the pivot mount rigid body. To obtain the view shown in
the figure, in the Mechanics Explorer toolstrip select the isometric
view button
.

To view a completed version of the pivot mount model, at the MATLAB command
prompt enter `smdoc_pivot_mount`

.

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