Three point, Lift Capacity

[imarobot]

My tractor has a lift force of 3860lbs at the lift points and 2980lbs 24" beyond the lift points. This is a difference of 880lbs in 2 feet. Is there a linear decrease in weight the further out you go? In other words, do you lose 440lbs lift force for every foot past the lift points?

(Mod Edit: Title change)

 

[RCW]

It’s not PTO (power take off) lift capacity, it’s the lift capacity of the 3 point hitch.

The reduced capacity at 24” is strictly a function of physics, and my mathematical abilities have waned over time.

I believe it’s linear, but I’m guessing some. I believe the relative distances have a bearing but I can’t come up with a mathematical equation off the top of my head to demonstrate it.

Good question that maybe some of the more technical guys can answer.

 

[GreensvilleJay]

Bet it isn't 'linear' but some gawdawful 'math' that involves all those things like SINEs,COSes, TANs and other 'weird' math we never really understood in highschool and KNEW we'd never use later.....

 

[North Idaho Wolfman]

PTO has Zero lift capacity.
That's the spinning shaft out the back, PTO= Power Take Off

The three point on the other hand, now that has lift.
And anything past 24" is pretty much worthless to configure to.

 

[Russell King]

Yes it is a linear formula for moments. See this site for information

Moment or Torque

Moment, or torque, is a turning force. ... Moment Force times the Distance at right angles.

www.mathsisfun.com

Now there may be some complex math involved in how much force the hydraulic system can exert onto the lower arms through the upper to lower arm linkages but I don’t think that would be in effect on the lower arm and how they move. Pull up with a pound force and you can move some weight at the pins, but less weight 24 inches past the pins.

There may be some alternate holes in the lower arms where the vertical lift linkages are attached on some tractors that would also effect how much weight can be lifted and how high.

 

[RCW]

Bet it isn't 'linear' but some gawdawful 'math' that involves all those things like SINEs,COSes, TANs and other 'weird' math we never really understood in highschool and KNEW we'd never use later.....

Jay - if you change the location the lifting point, you also change the relative length of the parts of the lifting arm.

Re-thinking the question, I don’t believe it’s linear…..there’s some “squared” stuff mixed in there.

Rattling my old noggin on that one…..not a bad thing.

Physics and it’s associated math was a LONG time ago…

 

[RCW]

Yes it is a linear formula for moments. See this site for information

Moment or Torque

Moment, or torque, is a turning force. ... Moment Force times the Distance at right angles.

www.mathsisfun.com

Now there may be some complex math involved in how much force the hydraulic system can exert onto the lower arms through the upper to lower arm linkages but I don’t think that would be in effect on the lower arm and how they move. Pull up with a pound force and you can move some weight at the pins, but less weight 24 inches past the pins.

There may be some alternate holes in the lower arms where the vertical lift linkages are attached on some tractors that would also effect how much weight can be lifted and how high.

Russell - I was hoping you would reply…

How does changing the lift-point change the capacity? Is that also linear?

 

[Russell King]

I think it would also be linear since it is just a distance change on the lever. But it is changing the geometry between the upper arms through pin and the lower arm. I would have to get into drawing a free body diagram to be sure but it seems linear at first thoughts.

on edit…

The change in position would not be linear since the vertical link is now more (or less) vertical than in previous position. That would chan the vertical component of lift using the sine (or cosine function from high school geometry class that you “will never use again”). The vertical component is the effective component that lifts the weight attached to the arms.

 

[GreensvilleJay]

to add more 'fuel to the fire'..... the 3PH doesn't rise straight up, goes in an 'arc', which changes depending on where the lift arms are pivoting relative to the top link pivot points. There's a few good drawing about this on the internet and someone must have 'done the math'....?

 

[Bee-Positive]

It should be somewhat linear, but it's complicated. Two different types of fulcrums involved. Upper arms pulling on the lower arms, the upper fulcrum values will be constant. The further out the load goes on the lower fulcrum the less load can be lifted. Fe x De = Fr x Dr

 

[imarobot]

Sorry for the wrong info, I meant 3 point not PTO. Thank you to whoever did that for fixing this for me.

 

[imarobot]

The reason I am asking is because I'm looking into getting a Del Morio Flipper Super 186 flail mower that has hydraulic shift and tilt capability. It weighs 1135 lbs and the back of it will extend out 83" from the rear tire. I'm trying to figure out if this is too heavy, especially when it is off the ground and extended fully out.
I could go with the Centurian Super 158 which is much lighter at 820 lbs, but would like the wider working width if possible.

 

[Russell King]

You would not want to lift it if it is extended out to the extremes. It would be sitting on its roller(s) as you were mowing.

But I guess you are saying you have to have it slightly off the ground to move it out to those extremes?

@McMXi has a Del Morino adjustable flair so would be able to give you some good advice. He should be along sometime soon.

 

[imarobot]

I would need to lift it to extend it or tilt it up in the vertical position. I realize that's a lot of weight hanging out there on one side of the tractor, that's why I'm questioning this.
I contacted Del Morino about this and their response was that it is too big for my tractor. I wanted to know what they meant by too big, weight or HP so I emailed them again. I got an answer back from a different person that it would work as long as I kept the tractor speed down if the PTO load gets strained while mowing. No mention of weight.
Asked around with a few dealers and also get varied answers, too heavy, pushing the PTO if I don't take it slow, will work just fine.
The end of the mower sticks out 7' so I I went ahead and calculated how much weight the lower links would support at this distance. Sounds like it's looks like it is not a linear drop in lift force, and I don't know if using the distance, the back of the mower hangs out there, but using 440 lbs/ft loss of lift and end of mower is out there 7' I come up with 780 lbs of lift capacity. May not be correct, not a linear drop in lift and maybe using the distance to the back of the mower isn't the right place to determine this, but don't know what else to use.
If this is somewhat accurate then a 1135 lb mower won't work.
Looks like I may need another, bigger tractor.

 

[North Idaho Wolfman]

It's both too heavy and requires more HP than your tractor is capable of producing.
With it side shifted it's going to put a huge strain on the three point system.

Will it work, maybe.
Will it work perfectly, probably not.

 

[imarobot]

Well, from all your comments and from other recommendations I could find, I agree that the Flipper Super 186 is too big for my tractor.
Ordered the Centurian Super 158 which my tractor and wallet will thank me for.
Size matters, but you gotta live with what you got.
Thanks for all your inputs. Still would like to know how to calculate the lift, but I see it ain't that easy to do.