Lift Capacity @ 24" for SubCompacts

[MARKMILES77]

I already said it may be de-rated to a lower number for the reasons you mentioned, which is exactally what you are saying. If it can't ift to its full potential, (max PSI) add weight to the front until it can.

If they are rating it lower than what the hydraulics can lift, that is de-rating it. If it is rated that low because that is the most the hydraulics can lift at the operating pressure, then it IS a geometry thing.

LD1 and Arrabil thanks for the information.
I'll have to take my ruler and measure the link arms and lift points on the GC2400 and BX2360 and see if that explains things!

Mark

 

[SPYDERLK]

This is the answer.

It all has to do with how each has designed the 3PH geometry. Mainly, where the actual lift points are on the arm itself in relation to the ball ends, where the link hooks to the tractor, and its relation to 24" behind the ball ends.

I am bored so I'll give you an example.

First, so we are on the same page with the termonology. There are 3 points that come into play on the lower 3PH arm. They are the point where the arm is affixed to the tractor, the point at which the lift arm connects (usually about half way between the tractor and the ball end) and then the ball end.


So... lets say that the lower arm is exactally 24" long and the lift point is right in the middle @ 12". For a rating of 1000lbs @ the ball ends, this would require an actual lift @ the vertical lifting arm of 2000lbs. Using that actual lift force, this would give a 12/48 (or 1:4) ratio @ 24" back. Or 500lbs.

Second example, Lower arm is lengthened 6" and the actual lift point is still 12" back from the tractor. Giving 18" from the lift point to the ball end.

In order to maintain the 1000lb rating 2 the ball ends, this would require a lift force on the arm of 2500 lbs. Now @ 24", which is actually 54" away from the tractor, we now have a 12/54 ratio. Multiply that be the 2500 lbs and you have 555lb rating @ 24".

This is somewhat of a crude example of how two tractors can have the same or similar rating at one point and differ at another.

Huh? ... :confused2: -- We have on the 3ph hookup a parallelogram linkage or some approximation. Such will lift the same or a significant portion of eye lift at any distance - depending on how exact an approximation his particular tractor has. In order for his tractors lift to decline so seriously behind the eyes it would mean that the //ogram approximation on his tractor is poor ... or else its an artificial mfg reduction of spec for safety reasons [tractor balance etc]. I know you understand this and dont see it in your post.
larry

 

[LD1]

Huh? ... :confused2: -- We have on the 3ph hookup a parallelogram linkage or some approximation. Such will lift the same or a significant portion of eye lift at any distance - depending on how exact an approximation his particular tractor has. In order for his tractors lift to decline so seriously behind the eyes it would mean that the //ogram approximation on his tractor is poor ... or else its an artificial mfg reduction of spec for safety reasons [tractor balance etc]. I know you understand this and dont see it in your post.
larry

Brain fart. What can I say

You are right though. Because the implement/load pivots around the ball end. My figures were assuming the lower was just lengthened 24". But it is not.

 

[LD1]

I forgot to add that the height of the toplink in relation to the two lower links can cause different ratings. Even on the same tractor if it has multiple toplink positions to choose from.

The lower the link is, the faster it tries to raise the back of the implement/load. Usually the highest toplink setting is the most parallel, raising the back of the attachment about the same as the front. For example, if you have a bushhog, the top setting will keep it the most level through out its travel. The lower settings will raise the back faster and cause the bushhogs tail wheel to be higher than the front if it is level to start with.

This is where the difference can occur. It takes more force to raise 500lbs 24" off the ground @ 24" back then it does to raise it only say 16" off the ground. So.....if one of the tractors has a greater deviation from parallel, it could cause a change. Or, if you are using something like a boom pole that doesn't use the tractors toplink, this could have to do with the geometry that I mentioned in my earlier post.

 

[arrabil]

The toplink cannot change anything related to max load capacity @ 24".

It can only change the object's position on the 3pt arms. THAT may change the load capacity because it may be further or closer than 24" but otherwise it has no effect on the 3pt's ability to lift.

 

[SPYDERLK]

The toplink cannot change anything related to max load capacity @ 24".

It can only change the object's position on the 3pt arms. THAT may change the load capacity because it may be further or closer than 24" but otherwise it has no effect on the 3pt's ability to lift.

Negatory. That is if you are actually meaning lift capacity. A 3ph is a parallelogram linkage, altho not a perfect one. Moving the pivot point of the top link definitely has an effect on how well the 3ph comes to a perfect "4 bar linkage". These lift a load straight and level, and lift force remains the same at any distance from the prime lifting pivots [analogous to the lift eyes in this case].
larry

 

[arrabil]

Can you show me where it says the 24" point needs to be straight and level on any manufacturers spec sheet? Can you show me where they specify a toplink configuration? What do they care how or why you install your implement?

How's this example.... I make a ball of cement for a ballast box. It weighs 550lbs. I hang it 24" behind the ball eyes on a bar that lets the cement ball spin freely. On the ball is a toplink mount. Will any of the three toplink configurations change the center of mass point? No, they will not. There will be 550# at 24" no matter how you spin the ball and no matter how high you lift it. And thats what the manufacturer is talking about.

All they're doing is saying you shouldn't buy a rotary cutter that weighs more than X pounds. You guys are talking about something else entirely.

 

[SPYDERLK]

Can you show me where it says the 24" point needs to be straight and level on any manufacturers spec sheet? Can you show me where they specify a toplink configuration? What do they care how or why you install your implement?

[How's this example.... I make a ball of cement for a ballast box. It weighs 550lbs. I hang it 24" behind the ball eyes on a bar that lets the cement ball spin freely. On the ball is a toplink mount.] Will any of the three toplink configurations change the center of mass point? No, they will not. There will be 550# at 24" no matter how you spin the ball and no matter how high you lift it. And thats what the manufacturer is talking about.

All they're doing is saying you shouldn't buy a rotary cutter that weighs more than X pounds. You guys are talking about something else entirely.

Now thats a setup that almost defys imagination. Sounds undoable.
larry

 

[LD1]

The toplink cannot change anything related to max load capacity @ 24".

It can only change the object's position on the 3pt arms. THAT may change the load capacity because it may be further or closer than 24" but otherwise it has no effect on the 3pt's ability to lift.

A perfect analogy for this is just a regular ol' forklift.

The forks are level and remain level throughout the raise. If it is capable of lifting 4000lbs, it will lift that at ant point on the forks with enough ballast. It doesn't matter how far away from the mast the load is. Again, with enough ballast to keep the rear down, there is the same amount of avaliable force at the tip of the forks as there is at the heel because the tip will raise exactally the same distance as the heel.

the tilt on the other hand has less and less force the farther down the fork you go. Because the lever acting on the tilt cylinders is getting longer and you are trying to move the load farther with the same given amount of cylinder travel.

This is what happens when you lower the toplinks mounting point on the tractor. It tries to move the load behind the ball links "farther" than the ball links themselves. So If you have a cylinder with a given diameter and a given operating pressure, and it is only capable of lifting 1000lbs at the eyes with said pressure, with a //ogram, it will lift that 1000lbs at ANY point back with enough ballast. BUT it you lower the toplink, you no longer have a true //ogram. It is trying to raise the load @ 24" a greater distance than at the ball ends. Like tilting back on a forklift. Thus the rating will be reduced.

So if the tractors in question have multiple places to hook the toplink, the top one will give the greatest capacity @ 24", and the lowest setting will give the least capacity. So it will all depend where they measured them at.

 

[tsteahr]

Can you show me where it says the 24" point needs to be straight and level on any manufacturers spec sheet? Can you show me where they specify a toplink configuration? What do they care how or why you install your implement?

How's this example.... I make a ball of cement for a ballast box. It weighs 550lbs. I hang it 24" behind the ball eyes on a bar that lets the cement ball spin freely. On the ball is a toplink mount. Will any of the three toplink configurations change the center of mass point? No, they will not. There will be 550# at 24" no matter how you spin the ball and no matter how high you lift it. And thats what the manufacturer is talking about.

All they're doing is saying you shouldn't buy a rotary cutter that weighs more than X pounds. You guys are talking about something else entirely.

Your example is not a viable 3ph mounting configuration and it will not lift the ball. We have to work within the physical geomatery of the 3ph configuration. In you example the ball will just sit on the ground, regardless of the position of the 3ph lower arms.

In order to get that ball 24" behind the ball eyes, you need to use a bar attached to the ball eyes with a pin. Now you need to have a top link attached to a fixed point to lift it. If you want to have the top link attached to the ball, the ball can not spin on its own axis. If it spins it will not lift. So either the ball remains fixed or the top link is attached to another point on the framework supporting the ball. Either way, as you shorten the top link the ball travels in a arc around the ball eyes. The shorter the top link the closer the ball CG is to the ball eyes (relative to direction of gravity). So Yes, the top link configuration does change the center of mass point.

That said, I agree with your point that the MFG is trying to saydon't buy a rotary cutter that weights more than x pounds.

I believe a significant contributing factor to the difference in ratings is the amount of lift height available at the ball eyes. Just like on a loader, there is a tradeoff between lift height and lift capacity. This is why some 3ph lift lower arms have 2 or more mounting holes for the links. To allow the user to choose between more lift height or more lift capacity. I am not aware of any manufacturers specifing lift height and lift capacity of their 3ph . Therefore we we only have half the information needed to accuratly compare the performance of various 3 point hitches.