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building bush hog need help with hyd motor choice

Discussion in 'Compact Equipment Attachments' started by wheeliewebb, Jun 18, 2010.

  1. wheeliewebb

    wheeliewebb Member

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    Trying to build a bush hog. Not familiar enough with hydraulics to figure out what motor i need. Building a 5ft bush hog and my machine is a new holland L170. Its 52 hp, 113ft lbs torque, 17.7gpm hyd flow (does not have high flow) 12.5 hyd capacity(reservior and system capacity) machine rpm is 3130 to 3300 high speed. If anyone knows who i could call that could help me or a part number for a motor that would work it would be greatly appreciated thanks....
     
  2. Deeretime

    Deeretime Senior Member

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    Montanna hydraulics
     
  3. TriHonu

    TriHonu Well-Known Member

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    Using the stated specs from Bobcats and Brush Wolf for their 60 in brush cutters and assuming you are direct driving the blade at 1:1 (no gear up or gear down) my math says:

    A hydraulic motor with a displacement of 3.3 cubic inches will spin the blade at 1239 rpm and the motor will create about 131 ft lbs of torque. The equivalent Bobcat mower is rated for material up to 3 inches in diameter.

    The smallest motor you should use is 1.8 cubic inch displacement. This will give you around 2273 rpm but only 71 ft lbs of torque.

    The largest motor you should use is 5.5 cubic inch displacement. This will give you 750 rpm and 218 ft lbs of torque.

    These numbers should be close (on the high side).

    You will have to consider what you are mowing and whether you want more power for difficult material or you have easy stuff and want travel faster.
     
  4. mowzall

    mowzall Active Member

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    You may also consider the type of hydraulic motor as these will impact theoretical calculations. eg, piston motor @ 95+% efficiency. gear motor 80% efficiency.
    Heat generation is a consideration with any hydraulic motor driven accessory.
    The knife bar/stump jumper design will also affect the choice motor re- the recovery rate and performance.
    The knife style (straight, updraft etc.) and tip speed for different materials should also be considered if your intent is for a specific type of work, meadow grass or brush or small trees or ?
    Are you building it because you can't buy one or because you just want to?
     
  5. stumpjumper83

    stumpjumper83 Senior Member

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    before you sink thousands into building one, I believe rhino offers theres for about 5k I think... But have fun building it if you stay the course. Put a heavy duty piece of steel on for the mower deck that area always need beefed up in the comercial models.
     
  6. wheeliewebb

    wheeliewebb Member

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    well i just figured i could build one one for about $1000. Buy an old three point bush hog with one wheel buy a hydraulic motor and couple it to the gear box. build a face plate and wa la got a mower for cheap. easier said than done.
     
  7. joispoi

    joispoi Senior Member

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    What's the hydraulic pressure on your machine? If it's 2,500 psi and 17.7 gpm, that gives you 25.8 hydraulic horse power. Factor in the efficiency of the motor you mount to the mower to calculate how much power is turning the blades.
    The 25.8 hp is probably closer to 25. If you find a motor that's 95% efficient, you've got 23.75 hp turning the mower. It's slightly underpowered for a 5 foot brush hog if you go by the 5hp per foot of diameter of the mower, but it should be okay.

    If you're replacing a tractor pto shaft with a hydraulic motor, you need a motor that turns at 540 rpm given 17.7 gpm.

    You're not going to find one that's rated "540" rpm. You'll have to pick what's closest. Here are a couple options.

    https://www.surpluscenter.com/sort.asp?catname=hydraulic&keyword=HML2
     
    Last edited: Jun 26, 2010
  8. willie59

    willie59 Super Moderator

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    Keep in mind another component that you may need to purchase is a crossover relief valve for the motor, unless you purchase a motor that has that built into it. Some skid loaders don't have port relief valves on the auxilliary circuits. If your machine has no port reliefs, and you don't use a crossover relief in the circuit, as soon as you release the control that sends oil to your brush cutter, it's going to come a very abrupt stop, like, KA-BLAM! Kinda hard on hyd components.
     
  9. joispoi

    joispoi Senior Member

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    This looks like it matches what you're looking for. https://www.surpluscenter.com/item.asp?item=9-7490&catname=hydraulic

    I would follow atco's advice on the cross over relief valve. Stumpjumper is right about reinforcing the deck. Most bush hogs are pretty light and take a real beating once you start using them in the heavy stuff.

    Post some pictures when you get started on it.
     
  10. HillsideVT

    HillsideVT Member

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    I'm just getting to the end of a similar project. Running mine on a Deere 250 std flow (15 gpm I think). I started with a new 5' king kutter bought cheap at auction. Already had hoses + QT plate. Originally I fitted it with a little Chinese motor that I had on hand, don't really know specs but would estimate 5 cubic inch or so. Whatever it is was not enough power so today I upgraded to a "Sonic" knockoff of a Char-Lynn 103-1028. It's between 9-10 cubic inch displacement and turns about 340 rpm. Much better, it's plenty fast, but at the upper limit of the skidsteer's capacity has no problem going through 4' tall grass and sumac, brambles, saplings up to 2" or so etc. X3 on the relief valve, I was using a check valve but too restrictive even for the small motor. Hope some of this is usseful, I'll be happy to post pics and/or video once I have a few posts to my name.
     
  11. HillsideVT

    HillsideVT Member

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    I'm just getting to the end of a similar project. Running mine on a Deere 250 std flow (15 gpm I think). I started with a new 5' king kutter bought cheap at auction. Already had hoses + QT plate. Originally I fitted it with a little Chinese motor that I had on hand, don't really know specs but would estimate 5 cubic inch or so. Whatever it is was not enough power so today I upgraded to a "Sonic" knockoff of a Char-Lynn 103-1028. $178 new on ebay. It's between 9-10 cubic inch displacement and turns about 340 rpm. Much better, it's plenty fast, but at the upper limit of the skidsteer's capacity has no problem going through 4' tall grass and sumac, brambles, saplings up to 2" or so etc. X3 on the relief valve, I was using a single 1/2" check valve but too restrictive even for the small motor. Hope some of this is usseful, I'll be happy to post pics and/or video once I have a few posts to my name.
     
  12. HillsideVT

    HillsideVT Member

    Joined:
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    Location:
    NEK, Vermont
    I'm just getting to the end of a similar project. Running mine on a Deere 250 std flow (15 gpm I think). I started with a new 5' king kutter bought cheap at auction. Already had hoses + QT plate. Originally I fitted it with a little Chinese motor that I had on hand, don't really know specs but would estimate 5 cubic inch or so. Whatever it is was not enough power so today I upgraded to a "Sonic" knockoff of a Char-Lynn 103-1028. $178 new on ebay. It's between 9-10 cubic inch displacement and turns only about 340 rpm. Much better, it's plenty fast, but at the upper limit of the skidsteer's capacity has no problem going through 4' tall grass and sumac, brambles, saplings up to 2" or so etc. X3 on the relief valve, I was using a single 1/2" check valve but too restrictive even for the small motor. Hope some of this is useful, I'll be happy to post pics and/or video once I have a few posts to my name.
     
  13. HillsideVT

    HillsideVT Member

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  14. amunderdog

    amunderdog Senior Member

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    That looked scary to me.
    Hope it was just a test run.
     
  15. bunkclimber

    bunkclimber Well-Known Member

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    hyd bush hog

    it's all fun until you hit that monster hornet's nest!:eek:
     
  16. HillsideVT

    HillsideVT Member

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    ^^^ hehe, i stepped in one last year with my stihl clearing saw strapped on. hopefully the skidsteer will drive away faster than i was able to run that day!
     
  17. BAKERELECT

    BAKERELECT New Member

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    Location:
    henryetta, ok
    building a brushhog

    this is my first post so bear with me. saw the brush hog that hilside built. it was great. I used the info that you posed for sizing my motor but I couldnt find a ( X3 ) crossover and I am not sure exactly what I am looking for?? I did find a crossover relief valve by prince item# 204601-2101 from northerntool.com is this the right item?? thanks for any help. the motor I am ordering isItem # 1042-2101 from northern tool as well.