Tractor Sizing How Much Can A Sub Compact Tractor lift?

[AxleHub]

Sorry to belabor the discussion on loader geometry, but I was looking at some pictures of the MF GC1715 and found it interesting that when the loader is at ground level the lift cylinder looks to be lower in the front than towards the back of the tractor and the angle formed between the lift cylinder and the lift arms is more acute that it would if the loader were a foot off the ground. My LB1914 also had a slightly more acute angle between loader and lift cylinder at ground level than at 1 foot above ground level.

So what does this mean for actual lifting. It is very well possible that the max lift force that the loader can generate occurs slightly above ground level (~1-2ft above). However, the tangent of the arc at 1ft is more vertical and this could prevent the loader from having more lift at slightly above ground level than ground level. On the GC1715, the breakout is 920 pounds and full lift is 870 pounds (manf. specs at the pin). This indicates that the decrease in lift arm to lift cylinder angle is almost entirely offset by the increase in angle between the tangent of the arc and verticle. This is very unlike my lb1914 which had the cylinder mounted much lower on the loader frame toward the rear of the tractor. Because it mounted lower in the back and higher in the front, the breakout force was much higher to start with, but the angle between the cylinder and lift arms more rapidly decreases as the lift arms are raised. The results was ~1600 pounds of lift at pins at ground level but only 850 pounds at full height. (nearly a 50% loss in lift!)

My current tractor is in between the examples above. Because the forward part of the lift cylinder attaches a little lower on the lift arms (favorable for keeping the angle between the cylinder and lift arms large as the arms are raised) compared to the cylinders on the LB1914, it conserves a greater percentage of lift at full height (break out ~3800, full lift ~2800) compared to the lB1914 but does not conserve as much lift % as the GC1715.

Every loader is a little different. The geometry determines the lift curve and I have only touched on the geometric possibilities here. I could design a loader geometry that would lift more at the top than the bottom or have >10x the break out compared to full height lift, but that would be silly, because you could never move a max load through the bottom portion of travel to use max lift at the top. I imagine that the loader geometry for the GC1715 was chosen to maximize lift throughout the range of motion without overwhelming whatever front axle was chosen for that machine. The breakout could have been easily and dramatically increased simply by mounting the rear of the cylinder lower with minimal impact on other specifications - this leads me to believe it was intentionally designed to limit breakout to protect the front axle.

A nice post Glade. I looked in my manual this a.m. and my hydraulic psi relief valve setting on the GC1715 is 1920 psi.

 

[TJP89]

:mur::mur::mur::mur::mur::mur:





Pressure goes higher as height goes higher BUT you still cannot exceed what the relief is set for.

IE: my relief is 2600psi.

raise the loader 1' off the ground with a load that requires 2400psi it lift. Darn near my limit.

As I continue to raise, at 2' height my gauge might be reading 2500psi. Then at 4' i might quit lifting all thogether because it NEEDS more than 2600psi to lift any higher.

THUS, you can either say the higher you lift, the more pressure is needed. OR the higher you lift, the less weight you can lift. Same thing.

ITs not rocket science, its accepted by every MFG, its a fact. loaders have more power at lower heights than at max height. Hundreds of stories on here of only being able to lift something a few feet when working near their max, many people with gauges like mine that show the same thing.

To me this is as silly as debating 2+2=4. So I am done. I have explained it many times and my words just get twisted to somehow magically pumps making more pressure than relief

Sorry to have started such a fistfight. I know that capacity goes down as height increases, just couldn't figure out why, as gravity is too weak to do it over that short of a distance. The geometry explanation makes sense. I was thinking of a straight lift, not accounting for the angles of the lift. You and k0ua made things clear, not sure why there's a huge argument over the relatively simple principles of hydraulics.

 

[4570Man]

At a certain point doesn't the load start moving back in? The loader moves in a arch, and the highest point is somewhere around the top of the hood.

 

[TJP89]

At a certain point doesn't the load start moving back in? The loader moves in a arch, and the highest point is somewhere around the top of the hood.

It might, but by then the load in on the hood, or worse, on you.

I don't think it's a perfect arc, as the loader arms aren't straight from the center, and power is not applied at the pivot point. It's some complex geometry, and I find it very intriguing, but I'm not a structual engineer.

 

[TomSeller]

I could design a loader geometry that would lift more at the top than the bottom .

How would you ever know how much you could lift at the top if you can't lift it at the bottom?

 

[gladehound]

How would you ever know how much you could lift at the top if you can't lift it at the bottom?

That is why I also said it would be silly to design such a loader That is unless you are trying to get in shape. You could tie the loader joy stick in the lift position and then walk around and lift up on the bucket until it gets high enough to lift on it's own. Then you need to run back to the tractor seat before the tractor tips over and falls on you. :laughing: Oh the safety police will be all over me for that.

 

[dragoneggs]

I think this thread just 'jumped the shark'.

 

[AxleHub]

I think this thread just 'jumped the shark'.

I've been told a couple scut users are going to be testing their machines this week as the rains clear.

 

[TomSeller]

I've been told a couple scut users are going to be testing their machines this week as the rains clear.

Let the competition begin.... I am sure no member would stretch the truth.

 

[AxleHub]

Let the competition begin.... I am sure no member would stretch the truth.

Ya, if guys were thinking its a red vs orange vs green "thing" . . then just a teensy bit of that word "competition" might slip in.

But I did mine for a different reason. I wanted real numbers, not "brochure speak" or opinions of big tractor owners who too often downplay scut potential to those considering new tractors. Scuts should earn their "due" . . not more or less. IMO

I figured there were lots of scut owners who might feel he same way and be curious what their units really can lift too.

I knew I couldn't use my bucket because the only convenient way to measure had to be with a known buildable weigjt like new concrete edgers or similar.

Time will tell if others participate