Lift Capacity @ 24" for SubCompacts

[tsteahr]

Because the load rotates, this cause the CoG of the load to be raised higher. Again, you cant get something for nothing. In order for the same amount of weight to be lifted higher, MORE force IS required. Because there is only a given amount of force avaliable at the lift arms (this is determined by the cylinder size, PSI, etc.) the load MUST be reduced in order to be lifted. The lower the toplink's position, the higher the mass is trying to be raised, thus the less weight it can lift.

Back to the W=F x D formula. It really is that simple. The 3PH is only capable of a given aount of work before Hydraulic cylinder size/PSI become the limiting factor. If it is only able to lift 1200lbs to a height of 24", it cannot lift that same mass to a height of 30". The mass MUST be reduce for work to remain the same. If the toplink and the lower links are equal length and parallel, ANY point is only trying to be raised 24", thus it can lift 1200lbs and still be within the avaliable work that the 3PH can do. With a lower/shorter toplink, you are asking that mass to be moved a greater distance with only the same avaliable work. Thus the Mass MUST be reuced. It really doesnt matter how much weight gets transfered or where or what is under compression or what is under tension. The only way to move that 1200lb mass a greater distance is to either increase the work avaliale or shed some weight.

LD1 is exactly right. What he is describing is the Method of Virtual Work. We started talking about that way back in post 27. There is a good condensed but somewhat technical discussion of this subject on Wikipedia if anyone is looking for the math behind it.

 

[SPYDERLK]

Since you're in the mood for thinking about my ideas all of a sudden, I'd like to add a couple more....

1) The rockshaft is capable of far more work than the 0" lift capacity indicates. Otherwise it would be a struggle to lift the max weight. I have seen a BX lift its max load and I wouldn't call it a struggle.

That means the capacity at 24" might not conform to any formula we can come up with. The capacity may be determined by something else.

2) Like what? You guys have said a number of times if the rockshaft can raise more, all we need is more ballast on the front to lift it. Yes and no. What if the axle bearings can't handle the ballast and the load? Or the transmission tunnel casting? Or the R1 or R3 tires? Or...

3) The manufacturer is not considering a 1000# static load. They are also taking into account that it swings, bounces, and hits rocks in the ground. That could result in twice the force or more being generated. What if your ballast plus the load plus the bouncing is enough to snap the tractor in half? We've seen it done from 3pt backhoes. So maybe they limit the 24" load so that you don't ballast against more and then drive through the woods?


No, it has to carry it. Because the lower arm is connected to the lift arms via a bar that pivots at both ends. That bar would have to be rigidly connected for the lowest mount not to carry any weight (in which case it also would be completely unnecessary). AND most importantly, because that lower point is the fulcrum against which the lift arms lever.

You have proved you are capable of throwing chaff into well considered explanations. I am convinced you wont ever be able to see the difference.
larry

 

[SPYDERLK]

It is correct that the force pulling down on the box is transferred to the toplink point. The toplink point on the box. That force HAS to go somewhere. That force added by pulling down is transmitted through the weight box to the eyes on the lower link. The big strong guy is pulling down on the top link. He is pulling down on the top of the weight box using the top link. That force goes straight to the lower link eyes.

No ... kinda. What you have not said is why the toplink is loaded at all. Its tension comes from the cantelevered load. There would be no tension in the TL if the load were carried in the vertical plane defined by the ball ends and TL eye. [Thats the lift rated at the ball eyes.] When you then suspend the same load rearward of that plane a cantelever situation comes into play, pulling straight back on the TL and pushing identically straight forward on the Lift Arms. In resisting these forces the TL pulls downward on the implement while the LAs push upward on the implement an equal amount. It is the torque applied by the cantelever to the plane of the articulated connection points that preserves the lift value.
larry

 

[tsteahr]

No ... kinda. What you have not said is why the toplink is loaded at all. Its tension comes from the cantelevered load. There would be no tension in the TL if the load were carried in the vertical plane defined by the ball ends and TL eye. [Thats the lift rated at the ball eyes.] When you then suspend the same load rearward of that plane a cantelever situation comes into play, pulling straight back on the TL and pushing identically straight forward on the Lift Arms. In resisting these forces the TL pulls downward on the implement while the LAs push upward on the implement an equal amount. It is the torque applied by the cantelever to the plane of the articulated connection points that preserves the lift value.
larry

You are absolutely right Larry. In my example I was talking about a weight box. The weight boxes I have seen are all cantilevered. But you are correct, there is no reason a weight box has to be cantilvered. If it is not cantilevered, if its mount pins align with its CG then we don't need the TL, just like you say.

Thanks for clearing that up :thumbsup:

 

[arrabil]

You have proved you are capable of throwing chaff into well considered explanations. I am convinced you wont ever be able to see the difference.

Pot meet kettle. BTW, did you ever find a parallel linkage with an unpowered link?

 

[tsteahr]

arrabil,

I felt we had made some progress. LD1 has described the "big picture" concept of the total work available to show why things cant be any other way. I went into detail about how all the forces shift around even though the weight is the same.

Do these ideas make any sense to you? I felt we were actually starting to make some progress a few posts ago...

 

[tsteahr]

Pot meet kettle. BTW, did you ever find a parallel linkage with an unpowered link?

Just a observation on this. A linkage system, parallel or otherwise, that does not have a powered link (a prime mover) would be called a truss. A truss can't directly move a load. Trusses are used all over. Bridges, the boom of cranes, etc.

 

[SPYDERLK]

arrabil,

I felt we had made some progress. LD1 has described the "big picture" concept of the total work available to show why things cant be any other way. I went into detail about how all the forces shift around even though the weight is the same.

Do these ideas make any sense to you? I felt we were actually starting to make some progress a few posts ago...

No, long explanations regardless of clarity will always rely on some assumptions of circumspectness and open mindedness to that not understood. This is absent here. I think it would be more likely to register by using the torque cantelevered on a plate attachment by a load behind the plate as an illustrative condition. Its easy to see how the effect on lift of increased distance of the load cancels out due to the proportionally increased torque exerted on the plate causing proportionally increasing opposing thrusts at the articulated connection points.
larry

 

[Don87]

I'd love to try the 'carry-all block test', but I have no carry all.

 

[Don87]

Here is the answer to the question asked earlier. On the GC2400 it is 10 inches between the ball ends on the tractor(center to center)(closest to the tractor), the arms are 21 inches long(center to center), it is 17 inches from the ball ends to the top link(center to center)
Oh, by the way, the GC2400 only has one place to attach the toplink on the tractor