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

 

[Rara Avis]

I still like my answer. "Call and ask"

jb

I agree, but he seemed to reject it...so I provide him with the math...

 

[MJPetersen]

Paul,

That is indeed an interesting site and shows how you also have to take into account the dipper movement. Thanks for finding that for us.

Mike

 

[dfkrug]

Untitled Document

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

Interesting site. Seems the standard (DIN) method of quoting dipper
stick digging force is not the maximum. The max occurs when the
bkt is curled all the way. The bkt curl point at which breakout force is
max is NOT the position at which the dipper stick force is max.

 

[wedge40]

Interesting site. Seems the standard (DIN) method of quoting dipper
stick digging force is not the maximum. The max occurs when the
bkt is curled all the way. The bkt curl point at which breakout force is
max is NOT the position at which the dipper stick force is max.

I found this on a site that sells backhoes. These are made in the US.
Please tell me if these numbers are close or are they bending the truth.
I'm interested in the forces.


Maximum digging depth....................................................................8?
Digging depth (two foot flat bottom) .................................................7?
Reach from swing pivot ...............................................................10?1
Transport height ..........................................................................7?0
Bucket clearance............................................................................6?
Bucket Rotation.............................................................................165ｰ
Swing arc.....................................................................................180ｰ
Stabilize spread down (Operating).....................................................7?
Stabilize spread up (Transporting) .....................................................5?
Bucket pry-out power - in excess of ...........................................6900 lbs.
Bucket curl power at cutting lip .................................................3200 lbs.
Crowd power at end of dipping stick ...........................................1692 lbs.
Lift at end of boom....................................................................760 lbs.
Lift at end of stick w/boom & dipper stick extended.........................455 lbs
Hydraulic system relief valve setting.. ......................................2000 P.S.I.
Hydraulic flow requirements ..............................................4.5 to 6 G.P.M.
Shipping weight (less bucket)......................................................860 lbs.
Recommended tractor size ....................................................40 to 45 HP
Boom cylinder..........................................................Bore 2.5?Stroke 20
Dipper stick cylinder .................................................Bore 2.5?Stroke 14
Bucket cylinder ........................................................Bore 2.5?Stoke 14
Swing cylinder (two).................................................Bore 2.5?Stroke 10
Stabilizer cylinder (two).............................................Bore 2.5?Stroke 10納/SIZE]

With a 2.5" bore and 2000 psi the force at the cylinder end is 9812.

 

[dfkrug]

WEDGE, the dipper stick force seems low, and I don't know what that
"bucket pry out power" is.

"Bucket pry-out power - in excess of ...........................................6900 lbs.
Bucket curl power at cutting lip .................................................3 200 lb"

The largest force quoted should be the bucket breakout force, which
seems to be the latter #, 3200.

What hoe is that you quoted?

 

[dfkrug]

With a 2.5" bore and 2000 psi the force at the cylinder end is 9812.

Yeah that is the force applied by the cylinder. Now you need to look
at the moment arms to determine what net force will be applied to the
end of the dipper, and to the teeth of the bkt.

 

[rbargeron]

The biggest "pryout" force happens when the back/bottom of the bucket is pressing against the ground and becomes the pivot point - like when you push with the boom while curling the bucket to break roots around a stump. The discussion above will give the force available from the bucket's curl linkage - then boom force can be added to the mix to get the max total force available at the teeth. The exact answer is usually not as important as whether or not it is enough

 

[dfkrug]

RBARGERON,
It is true that you can gain leverage when prying with the bkt
by pivoting on the bottom of the bkt. This transfers the curl
cylinder force to a shorter moment arm. This is how we can
tip up the edges of multi-thousand pound rocks. You can go
further than that, too. If you stick your bucket's teeth into
a fairly narrow gap, as between 2 rocks, you can apply many
more thousands of lbs of force, as now the moment arm pivot
is just a few inches.

 

[wedge40]

WEDGE, the dipper stick force seems low, and I don't know what that
"bucket pry out power" is.

"Bucket pry-out power - in excess of ...........................................6900 lbs.
Bucket curl power at cutting lip .................................................3 200 lb"

The largest force quoted should be the bucket breakout force, which
seems to be the latter #, 3200.

What hoe is that you quoted?

Its a Koyker KB75. They use to sell three different models but now they are down to just one.

 

[dfkrug]

Koyker. OK, that company has been around a while and is known
for its aftermkt loaders. They acquired the Kelly line of b/hs a
few years ago and both products were sold for a while.