calculate bucket pryout force.

[wedge40]

How would one go about calculating the bucket pryout force for a BH.
Since I know the basic force at the cylinder end. I'm guessing there is some simple dynamics formula I can use to figure this out. (I barely passed dynamics 25 years ago.)

Wedge

 

[john_bud]

Calculate the linear force from the cylinder.

Measure the distance from the cylinder force point on the bucket to the bucket pivot. Call this "A"

Measure the distance from the bucket pivot to the bucket lip. Call this "B"


Your BEST CASE force is the cylinder force* A/B. Other factors are in place with the variable geometry of the moving curved surfaces.


A slightly harder, but more accurate way is to call the company that made the hoe and ask.

jb

 

[wedge40]

I would ask the company but I don't speak chinese or korean.

I think I understand.. I'll try and draw a stick figure and see if I have it correct.

Wedge

 

[dfkrug]

Calculate the linear force from the cylinder.

Measure the distance from the cylinder force point on the bucket to the bucket pivot. Call this "A"

Measure the distance from the bucket pivot to the bucket lip. Call this "B"


Your BEST CASE force is the cylinder force* A/B. Other factors are in place with the variable geometry of the moving curved surfaces.


A slightly harder, but more accurate way is to call the company that made the hoe and ask.

jb

Good answer, JB.

Unfortuantely, backhoe published numbers (if any) are woefully incomplete,
for the most part. If a force is given, the manuf does not always tell at what
operating hydraulic pressure. If calling the company helps get better data,
I have not tried that.

As you say, there will be different curl forces delivered to the bkt teeth
at different curl positions. The greatest force is when A is greatest.

In trying to do a fairer measured comparison of b/hs out there, I have
tried to collect data on the cyl size and dipper stick ratio (A/B for the
dipper). I can then calulate max dipper stick force for different pressures. I
can only estimate the ID of the dipper cyl, however, unless it is opened
up or published.

 

[jmc]

I think most BH's have linkage between the cylinder and bucket, like in the attached picture. I don't think there is a simple formula for such an arrangement and calculating it by ignoring the linkage may be misleading.

John

 

[schmism]

its fairly simple statics

the hardest part is measureing the angles and distances.

in the case of the linkage, they simply provide a link to change the angle at which the force acts on the lever arm. (and or generate diffrent ranges of motion)

the red angle can be broken down from its vector from to 2 forces parrell and perpendcular to the arm (parrrell force on arm you toss out) perpendcular force (yellow) acts on the moment arm green (distance between the pins)

to find the break out force at the teeth, (second yellow line) you must take the moment around the pin (were the two green lines intersect)

M=Force*distance.

so F(breakout) = M(around pin)/distance from pin to teeth

PS youll need some trig to translate the purple number into the red number and the red number into the yellow number

NOTE: as the angle of the bucket changes, more (or less) force from the purple line is transfered to the red line, because of this the breakout force changes durring the entire sweep of the bucket.

if your really good youll slove the above 3 bar linkage problem in generic form, then plot the results to see how the force varries, then you could tell us the peak break out force and at what angle it occurs at. (hears a hit, its when the angle of the red linkage is directly in line with the purple cylinder force)

also remember that cylinder push/pull values are not the same due to area diffrences. In the case of an FEL bucket, your breakout force (upward) is the weaker of the 2 cylinder values. (this is the exact oppisite as shown in the hoe example above)

 

[jmc]

its fairly simple statics

Wedge,

"simple statics" isn't the same as "simple formula"! Schmism is correct in his analysis- you just need to remember your trig and how to resolve vectors...

John

 

[wedge40]

Wedge,

"simple statics" isn't the same as "simple formula"! Schmism is correct in his analysis- you just need to remember your trig and how to resolve vectors...

John

Did I forget to mention I got a D in statics as well.. LOL
I'm sure I can clear some of the cobwebs and figure it out. Besides it'll be fun. "I like math"

Wedge

 

[Rara Avis]

Untitled Document

Search for this on the page...Calculation of Breakout Force and Digging Force on Backhoe Attachment

 

[john_bud]

I still like my answer. "Call and ask"

jb