Calculating FEL Lift Capacity

[npalen]

This is probably a dumb question - but do you actually have the spec on the I.D. of the lift cylinder? Or does it just look like ~2" from the outside?

The outside diameter of the cylinder is 2.25" and the wall thickness is 0.125" leaving and inside diameter or bore of 2.00"
Was able to actually caliper the wall thickness at the rod end of the cylinder as the gland is recessed a bit.

 

[npalen]

Forgot to account for the angle of the cylinder. If the cylinder were mounted 90 degrees to the loader arm, then 100% of the cylinders force would be used for lift. But it is not. its mounted on a 29 degree angle. You have to take the Sine of the angle, and multiply that by the cylinders force. Whats left is the vertical component.

Then you have to account for the changing angle. The largest angle is with the loader at its lowest. Thus a loader has the most lift force at ground level usually called breakout force when reading specs. ITs usually twice as high as when fully raised. +

So, Raise the FEL to max height.

Re-measure the angle of the hydraulic cylinder. Re-calculate the math. The new number would be the lift to max height.

The "angle of the cylinder" is irrelevant when using "moments about a point" method of calculating forces. It's a simple matter of determining the torque that the cylinder force applies about the loader arm pivot point. (146,286 in. lb. based on 9420 lbs applied at 15.524" from the pivot in post #1 above) .

This torque can then be applied to any point about the pivot which, in this case, is applied vertically to the bucket pins which are 53.750" from the loader arm pivot. It is applied vertically due to gravity being applied against the weight being lifted in this case.

The decimal point is overkill in the numbers above. It's simply the measurement output from CAD. It can be set to show any number of decimal points including zero.

With that said, I do realize that some people use trigonometry (sine, cosine and tangent) to calculate forces based on angles.

 

[JCByrd24]

A couple of things:

- Your math is correct, you are correct about breaking it into moments vice doing the trig.
- You are neglecting a lot. Those cylinders will take 50lbs or more to overcome the friction if they are fresh I'd guess. The weight of the loader and bucket/forks is also directly off the number you got. Not to mention any friction in the pins/pivots.
- Finally, lift capacity is often stated at a much more usable height then what you've measured/drawn. You are closer to the spec of breakout force, which is often much higher. Raise your bucket to 3/4 of it's working height and re-measure. Your cylinder angle (or the moment arm that is currently ~15") will be greatly reduced, changing your equation and lowering your result.

 

[4570Man]

The loader lift is a lot higher at ground level. The 8xx pound rating is to full height. Subtract the weight of the loader and add in some margin of error and I'd say you could lift the number you came up with. Id be a bigger fan of just adding a measurable weight to the bucket until you can't lift it.

 

[gladehound]

All this time I was looking at your diagram as if the loader was in the full height position because that is the rating you were comparing against.

I agree with all those above that say your numbers look correct and I see absolutely no discrepancy between your numbers and the rating that you have because they are not at the same loader position.

I previously had a similar size loader and the full height rating at the pin was 850 pounds and the ground level rating at the pin was 1650 pounds. So big difference depending on loader position.

 

[s219]

The "angle of the cylinder" is irrelevant when using "moments about a point" method of calculating forces. It's a simple matter of determining the torque that the cylinder force applies about the loader arm pivot point. (146,286 in. lb. based on 9420 lbs applied at 15.524" from the pivot in post #1 above) .

Technically, it doesn't matter if you take the angle of the forces into account *or* you compute the effective perpendicular lever arm to the angled force -- either way you are working some trig in there if the linkage dimensions are based off the actual loader mechanism.

When computing a moment, in the end you are always doing the equivalent of a vector cross product, and r x f = |r|*|f|*sin(angle). Doesn't matter how you think about lumping in that angle, it's going to be there just the same.

 

[LD1]

Sorry, I am a bit rusty at calculating moments about a point. Not the way I normally calculate these kinds of things, but as they say, "there is more than one way to skin a cat".

But something still don't seem right.

Your 15.4xxx measurement doesn't appear to account for the angle of the cylinder. As those two points are fixed, and no matter how high the loader is raised....those two points don't change.

But the angle of the cylinder, and the force it can apply to the loader arm absolutely do change.

And I really doubt the cylinder only has a 1/8" wall. That part you measured is likely turned down smaller than the bore and threaded for the gland cap. I would be willing to bet the cylinders are a standard 45 mm cylinder. Pretty common for Kubota. That's 1.77", and gives you closer to a 1/4" wall thickness. Which is alot more realistic

 

[npalen]

Here is the drawing showing the geometry at lift height of 72" which is about maximum lift height for this particular FEL:

The 1618 pounds of theoretical lift force at this height compares to the 2,720 pounds at ground level.

I agree that 3/16" to 1/4" would be considered normal wall thickness for a cylinder tube. Using 3/16" wall in lieu of 1/8" wall would reduce the cylinder force by about 12-15% going from 2" bore to 1 7/8" bore.

The 15.4 (15.5 actually) measurement is a bit misleading as it is the distance from arm pivot perpendicular to the cylinder center line not the distance between the two pivot points.

The posts above make good points regarding friction etc. Taking all these factors into account including the smaller cylinder bore diameter probably makes the BF350 a reasonable model number.

 

[LD1]

That second drawing cleared things up for me as to how you were factoring in that cylinder angle. That initial 15.xxx inch measurement was perpendicular to the cylinder. At ground level, it looked as if you just took the actual measurement. So you are I deed compensating for the cylinder angle as the loader lifts.

I still believe you have 45mm cylinders. 50mm wouldn't allow enough wall thickness, and 45mm is the next smaller nominal size in metric, which is what Kubota uses.

For that matter, even sae, it wouldnt be something odd like 1-7/8. It's gonna be a nominal size, like 1-3/4".

Second.....both Kubota loaders that I have owned, and had gauges on, it takes about 600psi JUST to lift the loader frame and empty bucket. So that only gives you about 1000psi to lift your load.

So figure it with 1.77" cylinders and 1000psi and I'd bet you would be right on the mark.

I think you have just come to the realization that many on here overlook....and that is that a loader is alot stronger down low. Too many people only look at lift spec to max height, and overlook the breakout force rating. Which is what it can lift down low like digging out of a pile of dirt. Many people often mis-understand this and claim there loader is "underrated". When in fact people are just looking at the wrong ratings for what they are doing.

 

[npalen]

I believe you are correct on the metric size cylinders with 45mm probably spot on.
Here's one of many FEL spec charts showing the various nomenclature:
Farm King - Front-End Loaders
The "breakout force" seams to be misunderstood in some cases.