<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 13: Forces: Introduction > Step 13.1A: Stationary Rocker |
To understand how MechDesigner calculates and shows the Forces Vectors, we will start with a very basic kinematic-chain.
In this Step:
•The kinematic-chain is a stationary Rocker
•The Motion-Dimension FB does not have a wire connected to its input-connector.
•The Base-Value of the Motion-Dimension FB specifies the position of the Rocker.
•We add a Profile / Extrusion to add mass and inertia to the Rocker.
![]() Center-of-Mass Symbol(1) with Forces Display ON |
STEP 1: Add a Rocker
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STEP 2: Add the Profile and specify its shape
* From the shape of the Extrusion, MechDesigner calculates its Mass(kg), its Moment-of-Inertia(kg.m2), and its center-of-mass. In this case, because the sketch-loop is symmetrical and equal to the half the length of the Part - center-of-mass is 100mm from the Start-Point of the CAD-Line in the Part. The symbol for the center-of-mass is the |
There are two icons in the Force toolbar: Calculate and Display Force Vectors. |
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1.Mechanism-Editor: Click Force toolbar > Calculate Forces |
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1.Mechanism-Editor: Click Force toolbar > Display Force Vectors |
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When a minimum of one Part has mass, MechDesigner will display Force Vectors. The Force-Vectors give the direction and magnitude of each Force. Notes: If necessary, increase or decrease the length of the Force Vectors. If necessary, change the colours of the Force-Vectors with the Configure-Power-Source. See Force and Torque Vector Scale buttons. |
Force Analysis - Information:
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Move your mouse-pointer to the Part-Outline of the Rocker. You will see that the Force-Vectors that ACT ON the Rocker are Red Vertical Forces (N) acting on the Rocker - upwards is +ve
Moments (N.m) at the Pin-Joint - Counter-clockwise is +ve
Force Explanation of the RED Force Vectors and Moments
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Now move your mouse-pointer to the vertical Force-Vector that acts on the Base-Part. All vectors that ACT ON the Base-Part turn Red. There is:
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Make the Rocker Vertical: Edit the Base-Value in the Motion-Dimension FB to +90º, or 270º •My mouse-pointer is above the Part-Outline of the Rocker - the Part-Outline and the Force-Vector are Red. • Vertical Force = 9.807N. It is the equal to as when the Rocker is Horizontal. This is not a surprise. The Part has the same mass and it is the only joint through which the force can act. •Torque Moment = 0Nm. The Center-of-Mass of the Rocker above the Pin-Joint. Therefore, a Torque is not necessary to hold the Rocker. |