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  1. #1
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    Question Digging Force

    Hello,
    Has anyone done or heard about any working measurements on cylinder pressures to help calculate actual digging forces?

  2. #2
    J_J
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    Default Re: Digging Force

    The engineers calculate all that data before the device is even built. They also take in the fact that the cyl force may cause problems as to tipping, breakage, and may specify the pressure to stay within the bounders of safe operation.

    If you know the force of the cyl, and the mechanical relationship, you should be able to compute a figure.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  3. #3
    Silver Member indianaEPH's Avatar
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    Default Re: Digging Force

    John: In order to determine actual digging fore a lot more information would be required. IN addition to the cylinder force the geometry of the hoe/machine is required to calculate the force at the point of contact with the earth. This force will vary as the machine implement position varies. This is called kinematic analysis. There are probably calculators on the net that can help with this but in general it is a complex analysis.
    M59 TLB, 66" HD Grapple, Woods 72" BB, Kubota Trencher, Stump Bucket, Taylor 72" Box Blade, 7 ft back blade, woods 7 ft rock rake.

  4. #4
    J_J
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    Default Re: Digging Force

    If you look at the specs for a loader or a BH, they have already calculated the lift , breakout force, etc, for the attachment.

    If building on your own, and when finished, a hyd pull gage may help you in finding the force.

    For example.

    JCB*3CX 14FT (214)*Loader Backhoe
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  5. #5
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    Default Re: Digging Force

    I have worked for several OEM's in the off road equipment business over the last 18 years and I can tell you that they do lots of calculations before any steel is ever cut. Then we take the prototype and make sure it does what we thought it would do. This includes cylinder forces, structural stresses and tipping capacity.

    As far as calculating forces, it is certainly possible. Some machines, like cranes, do this already. But like indianaEPH said you need sensors to determine the angles of all the joints plus the real time cylinder pressures. In reality there will be some error due to cylinder seal drag and if your machine isn't level.

    ISZ

  6. #6
    Elite Member dfkrug's Avatar
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    05 Kioti CK30HST w/ Prairie Dog backhoe

    Default Re: Digging Force

    Quote Originally Posted by johngateley View Post
    Has anyone done or heard about any working measurements on cylinder pressures to help
    calculate actual digging forces?
    It is an interesting question. The calculations are quite easy and I have made them many
    times.

    For years, I have tried to do a fair comparison of backhoe attachments for compact
    tractors. The problem is that the manufacturers typically put digging forces into
    their spec sheets, but don't always tell you what the hydraulic pressures are. Consequently,
    it is hard to do a fair comparison between hoes.

    What I did is measure the dipper cylinder OD, the dipper stick length, and the dipper stick
    arm in the field. I then calculated the cylinder force as well at the "dipper stick ratio". The
    DSR is the ratio of the DS arm to the DS length. The DS arm is the distance between where
    the DS cylinder attaches to the DS, and the DS pivot point. I then calculated the digging
    force at the bucket pivot in the maximum case. The max is where the DS arm is perpendicular
    to the boom.

    Well, Excel is a wonderful tool, and I made a spreadsheet with the formulae entered. Here
    is a snapshot for some of the hoes I have measured. Note that I am able to compare them
    using 2 different hydraulic pressures 2000 and 2500psi. I had to estimate the cylinder IDs if
    I did not have that info. Cyls of this type usually have about 0.2" wall thickness.

    Also note that I have ignored the "breakout force" calculation. The BF depends on the
    bucket geometry (length of bkt pivot to end of tooth).
    Attached Thumbnails Attached Thumbnails Digging Force-hoe_specs.jpg  
    See my TBN projects at:
    http://mysite.verizon.net/resyfcgt/

  7. #7
    J_J
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    Default Re: Digging Force

    One reason for the lack of pressure statements is that the pressures are changing all the time when using the attachment as to the load imposed on the bucket, and other components in the attachment.

    The load factor determines the pressure.

    You could figure for max relief setting on the BH relief valve or loader relief valve for max force.

    If you change buckets, the figures for the loader and or BH may change.
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  8. #8
    Elite Member dfkrug's Avatar
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    Default Re: Digging Force

    Quote Originally Posted by J_J View Post
    One reason for the lack of pressure statements is that the pressures are
    changing all the time when using the attachment as to the load imposed on the bucket, and
    other components in the attachment.
    All manufacturerers quote max digging force using the dipper, and using the bkt cyl (the
    breakout force). Some of them state the test conditions (hydraulic RV setting). Some
    don't. Hard to make a comparison when shopping by spec sheet.

    The max forces are what we are all interested in, and that's partially determined
    by the RV setting, assuming there are no upstream RVs set lower. In using a backhoe,
    the user hits the RV setting on many, if not most strokes when digging a
    new hole.
    See my TBN projects at:
    http://mysite.verizon.net/resyfcgt/

  9. #9
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    Default Re: Digging Force

    As far as breakout force goes, all manufacturers with use whichever combination of cylinders gives them the higest numbers. But where it gets a little shady is with which bucket? They will use the shortest bucket they "sell" so they can publish the biggest number.

    For example, when I was working on skid steers, I was told that John deere does their capacity ratings with a small bucket designed only for foundry use. This keeps the CG of the load close to the front wheels and decreases the tipping moment, which increases the rated load. We could never prove this, but otherwise their numbers don't jive. Granted it doesn't up the numbers a lot, but some people just go off of the spec sheets.

    ISZ

  10. #10
    Elite Member dfkrug's Avatar
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    Default Re: Digging Force

    Quote Originally Posted by IceStationZebra View Post
    Granted it doesn't up the numbers a lot, but some people just go
    off of the spec sheets.
    Yes, they do, and they kinda have to if they have nothing else to go by.

    The bucket variable is why I did not even consider breakout force to campare hoes.

    It is hard to hide the force capabilities of the dipper. So a fairer comparison is
    possible.

    The other things I look at to compare are the diameter of the pins, the width of the
    dipper at the bkt pivot, and other design choices that add to the hoe's strength. One
    indicator of strength is the weight of the unit, sans bucket. That spec is not always
    published either.
    See my TBN projects at:
    http://mysite.verizon.net/resyfcgt/

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