Free Body Diagram of 3-Bar Linkage. Splitting the force?

Click For Summary

Discussion Overview

The discussion revolves around analyzing a free body diagram of a 3-bar linkage mechanism, particularly focusing on the forces acting on the system and how to account for them in calculations. Participants are addressing a homework problem related to the mechanics of the linkage, including the effects of angles and constraints on the system's behavior.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to account for the third angled beam in the force calculations.
  • Another participant points out that the mechanism, as drawn, is floating and lacks constraints, which would lead to unrealistic behavior.
  • A suggestion is made that linkages typically require angles greater than 25 degrees to function properly, contrasting with the original 4-degree angle.
  • Participants discuss the need for a proper free body diagram that clearly shows all forces acting on the linkage.
  • There is a mention of missing forces in the diagrams presented, indicating that not all components of the force system have been accounted for.
  • Questions arise about how to find the X and Y components of forces at specific points in the mechanism, particularly at the ground fixing pin.
  • Clarification is sought regarding the calculations for the required force "F ??", with participants discussing the separation of calculations for the sum of forces in the X and Y directions.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the angles used in the problem and the completeness of the free body diagrams. There is no consensus on the correct approach to calculating the forces, as multiple interpretations and methods are presented.

Contextual Notes

Participants highlight the importance of constraints in the mechanism and the need for accurate representations of forces in the free body diagram. There are unresolved questions regarding the specific forces that need to be included and how to calculate them accurately.

noodle951
Messages
9
Reaction score
0

Homework Statement


Hi, please see the attached file. I am trying to find the force as illustrated in the diagram.

Homework Equations


Picture1.png
[/B]

The Attempt at a Solution


I've found the force for the 4deg beam and therefore the horizontal beam however I am unsure how to take into account the third angled beam.

Thank you in advanced for any help. It is much appreciated.
 
Physics news on Phys.org
As drawn that mechanism is just floating in space with all the links loose relative to one another .

Any applied forces will distort the mechanism and accelerate the whole thing away from the starting location .

You need to have some constraints somewhere .
 
Last edited:
Hi Nidum, does this explain it better? The long horizontal beam represents an actuator. The mechanism is to tip a container.

Picture2.png
 
That's better . We don't want our problems propelled into outer space .

The mechanism won't actually function with the 4 deg angle . Linkages like that typically need 25 deg + to work .

Do you want to alter the problem to be a bit more realistic ?
 
Last edited:
Nidum said:
That's better . We don't want our problems propelled into outer space .

The mechanism won't actually function with the 4 deg angle . Linkages like that typically need 25 deg + to work .

Do you want to alter the problem to be a bit more realistic ?

Alright, handy to know! :)

So if i change the 4 deg angle to 25, I get: 9/(sin(25)) = 21.3KN on the upper angled beam.
 
Let's see a proper free body diagram for the linkage with all the forces acting shown clearly ..
 
Pic3.png


This ok?
 
There are three missing forces ...?
 
Pic4.png

This better? Not sure what other forces I need.
 
  • #10
Left hand side of diagram ? Two horizontal forces + one vertical force ?
 
  • #11
The horizontal component of F1? at either end of the beam? Then the vertical at the end of the first angled beam?
 
  • #12
Reaction forces from container fixing pin and ground fixing pin . Four in total but you are given one so three to find .

The mechanism and force system is symmetric about c/l so not much work to do .
 
Last edited:
  • #13
Something like this?
PIC5.png
 
  • #14
y mech.jpg
 
  • #15
Nidum said:
View attachment 114047

Ah that makes more sense. How would I go about finding the X and Y components at the lower ground fixing pin? Would I find the force going along the lower angled beam (hypotenuse) and go from there?

Also, once I've found the X and Y components, how do I go about finding the force required "F ??".

Thanks
 
  • #16
For the complete mechanism what can you say about the sum of externally applied forces in the X direction and in the Y direction ?
 
  • #17
So the force required "F ??" Is taken from the the sum of the X components and the sum of the Y components for the container and linkage fixing pin?
 
  • #18
Not quite - sum in X direction and sum in Y direction are separate calculations .
 

Similar threads

Beam boundary condition problem
  • · Replies 12 ·
Replies
12
Views
3K
Free body diagram of a preloaded system with a gasket
  • · Replies 2 ·
Replies
2
Views
2K
Engineering Static Vs Dynamic Force Analysis in Mechanism
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Force Generated By Leg Muscles in Free Body Diagrams
  • · Replies 8 ·
Replies
8
Views
2K
Truss Free Body Diagram & initial conditions
  • · Replies 5 ·
Replies
5
Views
2K
Free body diagram of a beam construction
  • · Replies 3 ·
Replies
3
Views
2K
Free body diagram from whole system-direction of forces in free-body d
  • · Replies 1 ·
Replies
1
Views
3K
Potential Mistake in Free-Body Diagram
  • · Replies 5 ·
Replies
5
Views
2K
Distributed weight of inclined beam.
  • · Replies 11 ·
Replies
11
Views
3K
Symbolic relationship between the input and output load
  • · Replies 1 ·
Replies
1
Views
2K