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Four Bar Mech. / Friction in Motion

Question asked by 1-M68PZO on Sep 17, 2009
Latest reply on Sep 22, 2009 by Ian Hogg

I have a simple, equal length-link, 4 bar mechanism that I am simulating using CosmosMotion. (Running SW2008 sp5.0)

 

Set-Up:

Mechanism is started at equilibrium

Gravity is applied in the negative Y direction

An arbitrary initial velocity is applied to link 3 (the coupling link)

An arbitrary friction is applied to the two concentric mates on link 3 (to eventually slow the mechanism to a stop at equilibrium). The frictions are the same, same sizes, same coefficient of friction.

A mass is added to link 3 and adjusted by 2.5" across the length (and further) of link 3

The two "Needles" are used to measure the angle of link 2 (the right link), they have no mass and are therefore (I hope) not included in the simulation

 

Objective:

I wanted to see how the location of Mass (center of gravity) affects the time it takes for the mechanism to reach equilibrium. (time it takes for the mechanism to stop swinging)

 

Problem:

The times the different configurations take to reach equilibrium are not consistent as would be expected. The configuration that lasts the longest is when the CG is directly over the left joint of link 3 but this result is not mirrored when the CG is over the right joint of link 3. I tried reversing the initial velocity to see if the graph of duration times would also reverse themselves, however they did not.

 

attached is a screen cap of the mechanism and graph of results

 

Why would the results be this way?

How is friction calculated in CosmosMotion (SolidWorks Motion)?

 

-Kyle Mason

CSWP

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