Conversion Factor for 3PH load capacity

[datanull]

Hi,

New member here.

I am trying to compare 3PH load capacity but they are measused differently. I found a thread that seemed to have a conversion but I was unable to get a seemingly reasonable answer. Perhaps I'm just too stupid.

How can I convert from say 2400lbs @ lift link ends to 24" behind link arms.

Thanks,

John King

 

[SPYDERLK]

You cant without an analysis of the lift geometry. Ideally, it is a parallelogram linkage. If it truly were it would lift the same at the balls and any distance behind them. The closeness with which the 3ph setup matches this determines how much loss in lift you get as you go back from the eyes. The match will vary with the placement of pivot points on the tractor and implement and many are selectable on both ends. Trust #s the manufacturer provides is a conservative average. The best you can achieve is 1:1 -- this would be if the implement rose straight w/o pivoting at all wrt the tractor. The worst would be if the implement pivoted the same as the lift arms [or more] as it rose. Real life will show a variable % loss across tractor brands due to the non ideal geometry achievable....and to a small extent Friction.
larry

 

[mwb]

The best you can achieve is 1:1 -- this would be if the implement rose straight w/o pivoting at all wrt the tractor. The worst would be if the implement pivoted the same as the lift arms [or more] as it rose. Real life will show a variable % loss across tractor brands due to the non ideal geometry achievable....and to a small extent Friction.
larry

I agree with your initial statement but I don't understand what you are trying to explain here. The simple fact is that the further the load is away from the tractor the less it can lift. It is a straight forward calculation of torque, mass x distance (lbs x inches).


o___________x___________________y----------z

o is the pivot (tractor end)
x is the lift arm linkage connected to the rockshaft (what the tractor lifts with)
y is the ball ends

if the length of o-x is 1 and x-y is 2 then the force y is 1/3 of the force at x.
if you extend the arm to z so the lenght of x-z = 3 then the force at z is 1/4 of x.

You do need the geometry (applicable lengths above) of the hitch to calculate the extended load capability but thats it. The rotation of hitch does not significantly affect the lift capability - certainly not for answering th OP.

Correct?

Cheers,
Mike

 

[nunyabinis]

mwb, that's the way I would figure it.


Just like measuring the tongue-load of a trailer using a bathroom scale, a balance beam and a fulcrum....only upside down.






.

 

[Reg]

Right;
Basically you just need to know the length of the lower lift arms.
Example arithmetic;
Spec sez: 2500 lbs at end of lower lift arms.
(Go measure 'em, center to center)
They are 33 inches long, so 33 x 2500 is the starting number.

24 inches behind that would be 57 inches behind their front end, so...
(33 x 2500) /57 lbs of lift force is available 24 inches behind the pins.
Another way of thinking about it is that you have 33/57 times whatever you have at the pins (33 inches back) this is about 58% and is a good/fair working rule of thumb - 1/2 if you want to make the arithmetic easy and/or be more conservative.

 

[SPYDERLK]

I agree with your initial statement but I don't understand what you are trying to explain here. The simple fact is that the further the load is away from the tractor the less it can lift. It is a straight forward calculation of torque, mass x distance (lbs x inches).[SNIP]
Correct?
Cheers,
Mike

No. When you lift something straight up w/o pivoting it torque does not enter in. If you lift a hammer straight up by the end of the handle or by the head you apply exactly the same upward force. The resistance you must apply to keep the heavy extended end from drooping is surely felt by you but doesnt amount to any work. If you have a boom pole to put on your tractor try lifting it from its tip, middle, and lift eyes while installed. The forces you must apply to lift it will be near the same at each place because it is going up w/o much pivot. Intuitively you would think that it would be a cinch to lift way back at the tip... All that leverage. The linkage cancels it for your lift, making you lift the same full weight of the pole and the tractor 3ph no matter where [rearward of the eyes] you lift from. Likewise for the tractor hydraulics, the linkage cancels the intuitive mechanical disadvantage of where on the length of the pole the weight is as the tractor lifts it.
larry
larry

 

[SPYDERLK]

I agree with your initial statement but I don't understand what you are trying to explain here. The simple fact is that the further the load is away from the tractor the less it can lift. It is a straight forward calculation of torque, mass x distance (lbs x inches).
o___________x___________________y----------z

o is the pivot (tractor end)
x is the lift arm linkage connected to the rockshaft (what the tractor lifts with)
y is the ball ends

if the length of o-x is 1 and x-y is 2 then the force y is 1/3 of the force at x.
if you extend the arm to z so the lenght of x-z = 3 then the force at z is 1/4 of x.

You do need the geometry (applicable lengths above) of the hitch to calculate the extended load capability but thats it. The rotation of hitch does not significantly affect the lift capability - certainly not for answering th OP.Correct?
Cheers,
Mike

mwb, that's the way I would figure it.
Just like measuring the tongue-load of a trailer using a bathroom scale, a balance beam and a fulcrum....only upside down.
.

Right;
Basically you just need to know the length of the lower lift arms.
Example arithmetic;
Spec sez: 2500 lbs at end of lower lift arms.
(Go measure 'em, center to center)
They are 33 inches long, so 33 x 2500 is the starting number.

24 inches behind that would be 57 inches behind their front end, so...
(33 x 2500) /57 lbs of lift force is available 24 inches behind the pins.
Another way of thinking about it is that you have 33/57 times whatever you have at the pins (33 inches back) this is about 58% and is a good/fair working rule of thumb - 1/2 if you want to make the arithmetic easy and/or be more conservative.

All on the wrong track. Take a look at how a laboratory balance scale works. The weighing platform is controled with a //ogram linkage so that it does not pivot as the balance arm moves. Consequently it does not matter where on the platform the sample to be weighed is placed.
larry

 

[Reg]

The point is that we don't know the torque available at the rocker arm.
If we knew that we could do ALL the arithmetic, well more of it.

What we DO know is what the manufacturers tell us and what we can measure.
On my tractor the lower link arms are 33 inches long and whatever the unknown torque available at the rocker arm is results in a quoted available lift force at the eyes.
I don't have the specs in front of me, but from memory it is about ~2500 lbs.

THIS is the effective lever;
O_________33_______^_______24____^
front......................2500 lbs...............x
eye;......................rear eye;

Solve for x.
In "fact" it is two levers, each supporting half the load, but we can represent them as one lever with the full load (-:

Hence the 33/57 arithmetic for 24 inches beyond the eyes.
YES, it is a shortcut, BUT it is accurate (accurate enough).

There is an unknown mechanism about halfway along the lower lift arm, it's details are irrelevant but some of it could be deduced,
e.g. IF the side link is AT the half way point then it would need to have a lifting force of 5,000 lbs (yeah, so what ?).
Similarly, if you measured the length of the rock shaft's arm and it;s angle to the side link (it almost certainly passes through 90 degrees) you could calculate the needed torque (again, "Yeah, so what ?).
Golly Gee; a few more details about the internal geometry and you could get all the way back to a recommended relief valve pressure (-:

Forget the lab scales, similarly forget any ideas about lifting 2000 lbs on an 8ft boom pole.
(-:

EDIT:
If you have a ASC flyer go to page 36.
They have "Lower Link Arms", which I have been calling "Lower Lift Arms".
Anyway, they are described as Cat 1 and 32 inches eye to eye.
I don't know how universal the Cat 1 spec is when it comes to this part, but an interesting thing about this part is that it has THREE(3) holes near it's center, I'm fairly sure mine have only one.
With these I could trade lift capacity for lift height (lift "range") simply by connecting the side links to different holes in the Link Arms.
Their on line catalogue item #11918 is here;
http://www.agrisupply.com/product.asp?pn=11918&sid=&eid=

:END EDIT

 

[SPYDERLK]

The point is that we don't know the torque available at the rocker arm.
If we knew that we could do ALL the arithmetic, well more of it.

What we DO know is what the manufacturers tell us and what we can measure.
On my tractor the lower link arms are 33 inches long and whatever the unknown torque available at the rocker arm is results in a quoted available lift force at the eyes.
I don't have the specs in front of me, but from memory it is about ~2500 lbs.

THIS is the effective lever;
O_________33_______^_______24____^
front......................2500 lbs...............x
eye;......................rear eye;

Solve for x.
(-:
Hence the 33/57 arithmetic for 24 inches beyond the eyes.
YES, it is a shortcut, BUT it is accurate (accurate enough).
[[[There is an unknown mechanism about halfway along the lower lift arm, it's details are irrelevant but some of it could be deduced,
e.g. IF the side link is AT the half way point then it would need to have a lifting force of 5,000 lbs (yeah, so what ?).
Similarly, if you measured the length of the rock shaft's arm and it;s angle to the side link (it almost certainly passes through 90 degrees) you could calculate the needed torque (again, "Yeah, so what ?).
Golly Gee; a few more details about the internal geometry and you could get all the way back to a recommended relief valve pressure (-:]]]
Forget the lab scales, similarly forget any ideas about lifting 2000 lbs on an 8ft boom pole.
(-:

[Yes, these things can be ignored because their resultant at the eyes is given.]....However, ignoring the fundamentals of a //ogram linkage by modeling it as a simple lever brings no understanding of the factors that cause its superior performance. Getting a "close" answer with your shortcut encourages you into thinking you are considering all the correct factors. You are not. The reason your answer comes close is that, in its normal lift and carry usage the linkage does not lend itself to a purely correct // setup so the manufacturer gives 24" numbers for the degraded setup that actually happens in normal use. These #s come out at about 80% of what is available at the eyes. [Not really all that close.]

In order to get 100% of what is available at the eyes all 4 arms must form a true //ogram. -- The top link must be the same length as the lift arms. Also, on the implement, the vert dimension from the pins to top link connection must be the same as that vertical dimension at the link connection points on the tractor body. Now all opposite arms will remain // as they move.

All that remains to test this straightforwardly is to get the vertical going segments of the //ogram truly vertical. [In many cases the tractor body lift link pins are well forward of the top link attach point. -- so the tractor rear would have to be elevated to acheive this.] Set up thusly an implement would rise straight and level and would rise exactly as far as the lift eyes. If you have 2K# lift at the eyes you would be able to lift 2k# minus the weight of the boompole at any point on your boompole.
larry

 

[gpflepsen]

Spyder, I'd reconsider thinking along those lines. The lift capacity is determined by a function of the weight (force) and the distance from the lift assembly, or moment (torque). You are completely discounting the moment part.