How to Calculate Pressure Exerted by C in a Lever and Fulcrum Configuration?

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Discussion Overview

The discussion revolves around calculating the pressure exerted by a piston in a lever and fulcrum configuration, specifically in the context of a bell crank mechanism. Participants explore the mechanics of force transfer, pressure calculations, and the implications of design choices in a system intended for compressing soil into a building block. The conversation includes theoretical considerations, practical applications, and the need for precise measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes a configuration involving a bell crank and a piston, seeking clarity on how to calculate the pressure exerted by the piston.
  • Another participant emphasizes the importance of working with forces in Newtons or pounds-force and mentions the relationship between applied and reaction forces in the system.
  • Discussion includes the recommended pressure of 20 MPa for compressing soil, with calculations suggesting that this translates to a significant force requirement on the piston.
  • Participants explore the implications of the lever's length and the angles involved in the bell crank mechanism, noting that the effectiveness of force transfer may vary with the angle of operation.
  • There is mention of a toggle effect that could amplify the force applied, with some participants seeking to understand how to calculate this effect within their specific application.
  • Clarifications are made regarding terminology, distinguishing between a bell crank and a toggle mechanism, and how these relate to the forces at play in the system.

Areas of Agreement / Disagreement

Participants express varying degrees of understanding regarding the mechanics involved, with some agreeing on the basic principles of force and pressure calculations while others raise questions about specific configurations and their implications. The discussion remains unresolved on several technical aspects, particularly regarding the toggle effect and the optimal angles for force application.

Contextual Notes

Participants note the need for consistent units in calculations and the importance of understanding the dimensions of the piston and lever arms. There are also references to the potential for high pressures and the implications of design choices on the effectiveness of the mechanism.

  • #181
Below is a sketch of how I visualize the crosspiece to lifting arm connections. (See above for details)

Crosspiece to Lifting Arm Connection.jpg
 
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  • #182
Ok, I think I got the problem I was having now.

The tube is welded to the crosspiece bars only.

No U piece.

I get what you mean re the lifting assembly at the other end.

Rough idea:

Showing 2" edge of tube with 1" thick bar with hole inserted with additions either side, shaft through them and case wall and piston etc.
lifter03.jpg
 
  • #183
That is a good start but now the challenge is finding a way to get the same strong reinforcement and load transfer connection between the axle plate and the arm that is now at the top end of the arms.

I am turning a number of variations for that connection running through my mind right now. I need to know what range of bars and plate you have or have access to that I can work with, including the width of the 1" bar you have. Once I have that information I will work on coming up with some connection suggestions.
 
  • #184
I have a number of the 1" which are actually 1 3/16 x 2 9/16 x 7 3/4 " that fit very nicely in the 2x3 tube. they are all pre-drilled for the shaft so I need to use them. Then I have 1/4", 3/16" plate.
 
  • #185
I think I have found a possible solution for connecting the tubing to the axle bar using your available materials, but, I need to know the distance between the inside edges of the two holes in the 7 3/4 long axle bar(s) and the length from the the inside edge of the axle hole to the opposite end of the bar.
 
  • #186
This is a drawing of the bar.

lifter04.jpg


The lower hole is where the axle goes (c).

The upper hole is serrated and gripped on to a serrated torsion bar suspension on the 'rail car' by clamping it on with a bolt through the small hole.

Can you describe in more detail which dimensions you are after?

note. after writing the above I reread your post and I think you mean between the two bars in the two arms. ?
 
  • #187
Using your above figure as reference, I am asking for the distance from the top edge of the bottom hole to the bottom edge of the top hole; and also, the distance from the top edge of the bottom hole to the top end of the bar.
 
  • #188
the distance from the top edge of the bottom hole to the bottom edge of the top hole is 3 3/16".

the distance from the top edge of the bottom hole to the top end of the bar is 5 1/2".
 
  • #189
OK, what I am going to suggest requires a fair amount of fabrication so I will make some illustrations to help you to understand it.
 
  • #190
One more question, What type and size of spacer on the axle between the inside of the lifting arm and the side of the box are you planning on using.
 
  • #191
my idea is to cut the lower part off a couple of bars and use them as the spacers.
 
  • #192
Are you going to drill them to fit around the shaft or just place them on the inner face of the lifting tube?
 
  • #193
I mean to cut the lower part that is pre-drilled.

lifter05.jpg
 

Attachments

  • upload_2016-12-5_9-56-19.png
    upload_2016-12-5_9-56-19.png
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  • #194
Ok, I can work with that.
 
  • #195
Attached is a suggested bottom connection design. The stacked 1/4" & 3/16" strips welded to the outside face of the axle bar are there to bring that to the 1 5/8" thickness required for a close side to side fit inside the 3 x 2 tubing for a strong welding attachment from the tube to the bar. I would have placed the 1/4" plate on one side of the bar and the 3/16' plate on the other but that will affect the inside 1" spacer clearance between the bar and body of the unit. Unfortunately, the top hole in the bar forced me to shorten the weld slot on the bar side without the added spacers.

I have also added reinforcing strips to the outside of the 2" faces of the tubing in the bottom region where there has been material removed for the welding slots in the 3" faces.

I made a composite using part of one of your figures to reduce my drafting time and the time of my response.

Review this layout and let me know what you think and any questions you have.

Arm Btm Connection Layout.jpg
 
Last edited:
  • #196
Ok, that's a neat setup. I'm sure I understand all of it. I can do that. At the moment I'm finishing off the cross piece and starting preparing the arms. I'll post pics later.
 
  • #197
current: car battery for visual scale.

fin03.JPG


yet to add strengthening strips.

Cut crosspiece inserts too short to have them protrude beyond outer strips.

Arms not cut to length. Don't want to make mistake again of precutting to find mistake later.

found I've cut the c shaft too short. ie can't add third outer layer. I think I was miscalculating/mismeasuring for the inner strips.
 
  • #198
Explain exactly what you mean by the "third outer layer".

Be sure to make a good weld connection between the crosspiece and the bottom slot and the reinforcing plates
 
  • #199
I mean this layer pointed to in red. The rod reaches to the red dotted line.

lifter03.jpg
 
  • #200
OK, I don't see that as any issue for the arm or the end attachment as long as you are still going to use the two inserted spacer plates for welding.
 
  • #201
Yes I will. That's good. Thank you.
 

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