﻿ Getting Started Tutorials - MechDesigner > Tutorial 13: Forces: Introduction  > Step 13.4: Rocker [Cam-Follower] and 2D Cam

# Step 13.4: A Rocker Driven by a 2D-Cam

### Add a 2D-Cam and Configure the Power Source

When we add a 2D-Cam, we must also Configure the Power Source

In this Step 13.4, we will

1.Delete the Spring FB

2.Delete the wire from Linear-Motion FB to the Motion-Dimension FB

3.Do Add Polyline and Add Profile to extrude the 2D-Cam as a Solid (Note this is not needed to  establish the  Contact-Force

4.Configure the Power Source. to make the 2D-Cam the Power Source for the Cam-Follower.

#### A Stationary Rocker and a 2D-Cam

Give the Cam a Mass

Note: We do not need to Give the Cam a Mass. However, it is a good opportunity to remind you of how you can, if you really want to, do Add Polyline and Add Profile. to extrude the 2D-Cam as a Solid.

STEP 1: Add a Polyline to the 2D-Cam

Before we can add a Profile to a 2D-Cam, we must first add to it a Polyline.

 1.Mechanism-Editor: Click the Home (or ALT+H ) key on your keyboard. 2.Mechanism-Editor: Click Solids toolbar > Add Polyline 3.Mechanism-Editor: Click the 2D-Cam shape 4.Click in the Command-Manager

STEP 2: The Polyline of a 2D-Cam is a sketch-loop. We can add a Profile to a sketch-loop

 1.Mechanism-Editor: Click Solids toolbar >Add Profile 2.Mechanism-Editor: Click the Polyline (sketch-loop) 3.Click in the Command-Manager

You can see the force and moment that act on the Rocker are the same as before, 19.61N and 2.942Nm, respectively.

The Problem : Where is the Contact Force between the Cam and Cam-Follower?

(For convenience, I have made the mass of the 2D-Cam equal 4kg (editing its Density). Therefore, there is a Reaction Force from the Base-Part of 39.227N to support the Cam).

Configure the Power Source

 Why is the Cam-Force zero? In the image to the left, there are two Power Source ( 2 Motors) •A Motor to drive the Rocker •A Motor to drive the Cam-shaft There is usually ONE motor to drive this mechanism! This is because: •Motor does not really exist. The cam drives the Cam-Follower / Rocker, and not a motor. •Motor is OK. It rotates the Cam-shaft We must reconfigure the Power Source to make the 2D-Cam drive the Rocker. To open the Configure Power Source dialog-box: In the Kinematics-Tree, do these three clicks A: Click the Kinematic-Chain that includes the Cam-Follower B: Right-Click the Kinematic-Chain C: Click Configure Power Source STEP 12: Or: A: Click the kinematic-chain with the Cam-Follower B: Click Force Toolbar >Configure Power Source The Configure Power Source dialog-box is now open. Power Source tab > Box Motion-Dimensions  | Motor Elements Select the Motion-Dimension for which you want to configure the Power Source. STEP 13: In box : click the Mot-Dim Rocker Box lists the possible Power-Sources (or Motor Elements) that can drive the Motion-Dimension you select in box •Pin-Joint – icon to indicate it is the default Power-Source •2D-Cam - We want to use the 2D-Cam as the Power-Source STEP 14: In box : Click the 2D-Cam Now, the icon is to the left of the 2D-Cam to indicate the 2D-Cam is the Power-Source Also you should see the 2D-Cam in box  as the Motor-Element for the Mot-Dim Rocker STEP 15: Click to close the dialog You should see that: 1.The Motor symbol is not at the Pin-Joint of the Cam-Follower Rocker   2.There is not a Torque vector at the Cam-Follower Pin-Joint. This 2D-Cam does not need a torque because it does not do useful work. The Cam simply supports the mass of the Cam-Follower and Cam-Follower Roller. 3.Action and reaction forces at the Cam Contact 4.The Motor symbol at the Cam-Shaft 5.The Action and Reaction Forces at the center of the 2D-Cam  are now 53.94N, The center of the Cam must support the weight (m.g) of the Cam-Follower/Rocker and the Cam-Follower Roller