So you apparently still dont know what Ive said. You continue to throw argument into the mix while making re statements of virtually identical descriptions I have made and original misstatements of things you falsely attribute to my statements. The limit to the load is the force at the eyes. The limit to how far back that load can be is the back tipping point of the tractor. Nothing will break unless you add front weight to keep the tractor from tipping - - or maybe drive around over bumps while teetering back and forth. Most people would catch that indication and call it a clue.
larry
Well, I just reread this lengthy thread and have discovered for myself where the "cognitive disorder" has manifest.
Spyderlk is using the fixed "tipping" of the tractor as the limiting condition. No front weights, no loader filled with gravel etc. I'm not sure why, as this is never part of any tractor specification I have heard of, and I know that makers don't "uprate" the 3ph lifting capacity when some type of front ballast is present.
This is the clue for the clueless that Larry has been talking about. ;-)
A second "disorder in thinking" is in regards to the perfect parallelogram logic. Yes, there are some interesting effects in a four bar link, but the most important one is that without some load bearing support, such as triangulation or an ADDITIONAL SUPPORTING MEMBER. a parallel motion linkage will just lay flat on the ground. Lifting nothing.
So that returns the logic back to answer the question of what does do the lifting, and what are the limitations. Manufacturers state limits for a reason, and it's not because they cant find equal length top and bottom links.
For me it gets back to one of the very first responses that brings up the moment arm concept. and for my experience, I have never seen a tractor 3ph that did not make use of lifting arms rotating on a rock shaft.
So yes, one can make a parallel motion linkage that will translate any load to it's end pins. And if those end pins are the element calculated for failure at the rated lifting capacity. There will be the case proposed by Larry.
But, If the 3ph lifting capability is limited by hydraulic pressure on the 3ph actuating cylinder(s), along with the lifting arm length (leverage. moment, torque, call it what you will) Then we have the situation on 99.99% of all tractors being discussed on these forums, and the load ratings can be compared with simple proportional math. Simple levers. What the makers should be posting IN ADDITION to lift rating is "maximum lifting force at the lift arm ends", and for those machines that offer hydraulic down pressure, negative values as well ;-)
PS , the balance scale example was used exactly in REVERSE of the required purpose, for the sliding weights (the lifted load) moves along the scale beam. Think about it, which end is being "lifted?
Also, in regard to "lifting the boom pole" from various distances. Again backwards example. What would the lifting arms and hydraulic cylinder be experiencing in each case?
Shared perspective is so difficult, but comparing lifting performance of tractor three point hitches is not so hard once the details are considered.
