Calculating FEL Lift Capacity

[TheMan419]

Or just stack sacks of concrete in the bucket to get a real world number.

They do the same with bridges.

Calvin and Hobbes Comic Strip, November 26, 1986
on GoComics.com

 

[gladehound]

Can you show us the geometry of the compound linkage between bucket and cylinders? I would have thought that this linkage would tend to maintain a more consistent lever arm advantage thru the full motion. Is there another reason for the compound linkage?
We used that type of linkage extensively in farm tillage equipment design for folding wing sections to near 180 degrees.

Here is a picture of the compound linkage and I'm guessing this is very similar to just about every CUT sold today.



I did not use any geometry in this compound linkage to calculate anything. I am only using the surface area for the cylinders, stroke, relief pressure and how much the attachment plate rotates.

From LD-1

As someone else said, that ~3000 is probably the minimum.

As to your extremely high number.....where did you get the 115 degrees from. I think that is a bit on the low side.

My LA844 loader has the same size cylinders. And they list 3 rollback measurements. 4400# at ground level, 4300# at 1500mm and 2800# at max height.

Not sure why that correlate the rollback with a lift height. I assume at each height, it is measured with the bucket bottom flat. So at the 3 different points, the bucket cylinders/linkages are extended more and more as the loader is raised.

Kubota also has a chart in the manual illustrating the curve. Fully dumped bucket is gonna be the weakest on rollback. The more it rolls back, the stronger it gets.....to a point. Then will start to get weaker again before being curled all the way. The strongest point is somewhere around bucket level on the ground. What is the distance between the bucket pins. (pin in loader arm to pin in 4-bar linkage that attaches to bucket.) .

I think you are right about 115 degrees being low. I got it from summing the angle of dump and roll back provided on the loader specification sheet. But I have now found so many discrepancies in Kioti's literature that I would not be surprised if it is incorrect. They seriously need better editors! In fact, from watching how far my forks can rotate there is no way it is only 115 degrees but I don't have the correct spec and I'm more interested in positions where I most often use the forks so I'll focus on those (can you share the curl force curve for the Kubota? I'm interested in what that curve looks like as it is probably similar)

Today, I put my forks flat on the ground like in the picture. I put a little pressure on the lift cylinders just so they wouldn't droop when I curled the forks up. The I curled the forks up exactly 10 inches from the start position and measured cylinder travel. It was 1 and 1/8 inch. I did the same with the pins at 59" because I think that is a height manufacturers sometimes list for taking loads off trucks. With forks parallel to the ground I again curled the tips up 10" and measured cylinder travel. It was 1 and 11/32nds.

With actual measurements of the leverage the fork tips have on the cylinders rather than errant specs, I can calculate what should be some more reasonable numbers.

So the important numbers for ground level roll back are...
2.16" cylinder bore
2556 psi relief pressure
1.18" rod diameter
10" vertical movement at fork tips (61" beyond pins) results in 1.125" cylinder movement

When retracting, the cylinders produce 13,135 pounds of force. 61 inches out, the mechanical disadvantage is 1.125/10 or 0.1125 resulting in 1,478 pounds of lift 61" beyond the pins. back this off to 19.5" beyond the pins (where Kioti gives the 2990 spec) and it's 4,623 pounds - not surprisingly very similar to the LA844. Subtract off standard bucket weight and close to identical! And near identical to the spec tractordata.come gives for the KL401 (4633 at ground level) which is identical to my KL402 except for sub frame and loader valve position. So I'm fairly sure this is the right number now.

Doing the same at 59" high gave 5,518 pounds because the linkage allows 1 and 11/32" cylinder travel for the same 10 inches of fork tip movement.

I only calculated at 19.5" because that's where Kioti lists the spec. 36" is a more important distance for me (center of a 4 foot pallet on my forks) and at that point it calculates to ~2,500 pounds at ground level.

OK, Next problem!

 

[LD1]

I think you are right about 115 degrees being low. I got it from summing the angle of dump and roll back provided on the loader specification sheet. But I have now found so many discrepancies in Kioti's literature that I would not be surprised if it is incorrect. They seriously need better editors! In fact, from watching how far my forks can rotate there is no way it is only 115 degrees but I don't have the correct spec and I'm more interested in positions where I most often use the forks so I'll focus on those (can you share the curl force curve for the Kubota? I'm interested in what that curve looks like as it is probably similar)

Nothing wrong with the kioti literature here. Its operator error in using the specs

The max rollback and max dump that you used to get the 115 degree number are going to be correct.

Max dump is usually measured at max loader height. Max roll back is usually measured at ground level. You you are not accounting for the additional rollback that comes from just raising the loader to max height. (That extra rollback that causes you to either A. dump while you are raising the loader, or B. Spill your load all over your hood.

As to calculating at 19.5" forward vs 36.........19.5" is pretty standard (500mm) on these sized tractors....because thats roughly where the bucket edge will be. Giving a 36" spec instead would be useless to anyone not running forks, because tractors only come standard with the bucket.

But would be simple to calculate a 39" measurement using forks.......just take half the 19.5" measurement and your good. Close enough to 36" to be useful.

Bigger tractors often use 800mm (31.5") forward instead of the 500mm/19.5", as their loaders and buckets are bigger.

 

[davedj1]

OK, quick question before I continue. Is the relief in the valve that I am going to use what determines system pressure? This one is set to 2000 psi
2 SPOOL 8 GPM PRINCE MB21GB5C1 DA VALVE W/FLOAT

 

[gladehound]

Nothing wrong with the kioti literature here. Its operator error in using the specs

The max rollback and max dump that you used to get the 115 degree number are going to be correct.

Max dump is usually measured at max loader height. Max roll back is usually measured at ground level. You you are not accounting for the additional rollback that comes from just raising the loader to max height. (That extra rollback that causes you to either A. dump while you are raising the loader, or B. Spill your load all over your hood.

As to calculating at 19.5" forward vs 36.........19.5" is pretty standard (500mm) on these sized tractors....because thats roughly where the bucket edge will be. Giving a 36" spec instead would be useless to anyone not running forks, because tractors only come standard with the bucket.

But would be simple to calculate a 39" measurement using forks.......just take half the 19.5" measurement and your good. Close enough to 36" to be useful.

Bigger tractors often use 800mm (31.5") forward instead of the 500mm/19.5", as their loaders and buckets are bigger.

Thanks for clarification on the max roll back and max dump specs. Makes sense now. So now I learned 2 things in this thread! :thumbsup:

Why take half the 19.5" measurement to approximate 36" when you could just take 19.5/36 to calculate it!

Incidentally, Kioti's 2990 spec at 19.5" matches up almost perfectly to what I calculate for 31.5" forward of the pins. I know they use 31.5" for some of their larger tractors. Things that make you go hmmm...

Pardon me for questioning Kioti specs - It's just that the marketing literature and the shop manual for my tractor disagree on some specs such as PTO hp and Speed in gear. Speed in gear is an obvious error in the shop manual. PTO hp, who knows, marketing literature says ~35hp, shop manual says ~38hp. But it's a gear tractor so and the 35hp would put it lower than the same engine with HST. Doubtful. So I now have a trust issue with Kioti specs.

LD-1 - would still appreciate if you could post the roll back force graph that you have for your Kubota!

 

[gladehound]

OK, quick question before I continue. Is the relief in the valve that I am going to use what determines system pressure? This one is set to 2000 psi
2 SPOOL 8 GPM PRINCE MB21GB5C1 DA VALVE W/FLOAT

If that is the lowest pressure relief setting in the system than yes. You also have a main relief for the tractor. If the main relief is set to a lower pressure, that will limit the max pressure to the loader and your loader relief will never go into relief. If the main relief for the tractor is set higher than 2000 psi, than you will have 2000 psi to the loader limited by the loader relief valve.

 

[gladehound]

LD-1, these are the buckets I use most often (in addition to forks), thus the 19.5" isn't too meaningful to me... I don't think the stock bucket has even been on the tractor in the past year!



I have a project coming up where I'm going to use a boom pole. So I really want to understand the forces involved and what the tractor can handle before using the boom pole. Since some of the things I need to lift with the boom pole are of unknown weight, I've ordered a 1,100 pound hanging scale with hooks top and bottom so that I have an idea what I'm getting into before I get into it.

Don't worry, have a separate spread sheet to figure out ballast needs. In addition to the 1000 pounds of fill in the tires, the cage and me, all of which = about 1,500 extra pounds on the rear. I plan to put 1,700 pounds on the 3pt and most of that weight will be inches from the ground.

 

[Xfaxman]

--------------------

I have a project coming up where I'm going to use a boom pole. So I really want to understand the forces involved and what the tractor can handle before using the boom pole. Since some of the things I need to lift with the boom pole are of unknown weight, I've ordered a 1,100 pound hanging scale with hooks top and bottom so that I have an idea what I'm getting into before I get into it.

------------------------

I predict that you will wish you had ordered a higher capacity scale.

My loader lift was rated at 4,400 pounds so I ordered a 5,000 pound scale, not enough, OF means Overflow.

More pictures:http://www.tractorbynet.com/forums/...quipment/275747-v417-max-lift.html?highlight=

It does get used a lot for weighing things. :thumbsup:

 

[npalen]

Come on guys! Now we all think we must have a digital hoist scale.:licking:

 

[Xfaxman]

Well, since I can't calculate the lift capacity, It was my best option.

I used to have a 1,000 pound platform scale and was going to get a higher capacity, but since you have to pick up things to put on the platform, I got the crane scale. And it was cheaper than the platform scale that I was looking at.

 

[Fallon]

I keep thinking about permanent mounting a pressure gauge on my loader lift circuit where I could see it well from the seat. Would probably need to come up with a pressure to weight chart, but it would be able to tell you data on the fly for everything.

Might only be accurate at a particular height though. Not to mention different implements & how close the load is to the pins would affect observed pressure vs. actual weight.

 

[gladehound]

I predict that you will wish you had ordered a higher capacity scale.

It was only $50. I have a lot of pulleys so can easily weigh anything I can lift by putting it on the leveraged side of the blocks.

 

[davedj1]

If that is the lowest pressure relief setting in the system than yes. You also have a main relief for the tractor. If the main relief is set to a lower pressure, that will limit the max pressure to the loader and your loader relief will never go into relief. If the main relief for the tractor is set higher than 2000 psi, than you will have 2000 psi to the loader limited by the loader relief valve.

I am using an auxiliary pump that will be added to the front of my tractor. Should I put a pressure relief before the valve? I hate to keep cluttering up this thread but it has so much good info and such great advice. I will start another one if you all think I should.

 

[npalen]

I have no objection as the original poster but can't speak for everyone.

 

[LD1]

LD-1 - would still appreciate if you could post the roll back force graph that you have for your Kubota!

Sorry for the delay. Been a busy last few days

Here is what a typical loader force curve looks like. 1 KN = 225#

I have a project coming up where I'm going to use a boom pole. So I really want to understand the forces involved and what the tractor can handle before using the boom pole. Since some of the things I need to lift with the boom pole are of unknown weight, I've ordered a 1,100 pound hanging scale with hooks top and bottom so that I have an idea what I'm getting into before I get into it.

Don't worry, have a separate spread sheet to figure out ballast needs. In addition to the 1000 pounds of fill in the tires, the cage and me, all of which = about 1,500 extra pounds on the rear. I plan to put 1,700 pounds on the 3pt and most of that weight will be inches from the ground.

Most modern loaders have a stronger curl force than lift force at/around the bucket edge.

But as the load is moved forward.....the curl strength drops off much quicker than lift force. Usually to the point that they are about equal at the tip of 48" forks.

A boom pole, say 8 or 10' long on the loader......you are gonna find that your curl force is weaker than the loader lift cylinders.

 

[gladehound]

.....the curl strength drops off much quicker than lift force. Usually to the point that they are about equal at the tip of 48" forks.

A boom pole, say 8 or 10' long on the loader......you are gonna find that your curl force is weaker than the loader lift cylinders.

Thus the scale. at 10ft past the pins, my lift cylinders will lift more than twice what my curl cylinders will lift. Don't want to pop a cylinder!:shocked:

 

[LD1]

You really should bet a gauge, attach it to a tee, and a pair of QD fittings. Insert it inline with the curl cylinders so you can monitor the pressure those cylinders are seeing while lifting with the lift cylinders.

I have a gauge that I can move to any port on my loader. IT normally spends its time on the lift circuit.....with a little math on the fly, I can get a pretty rough estimation of how heavy something is I am lifting. But with the QD's and Tee, its easy to put it on any of the 4 circuits.

When I had my L3400, I attached a make-shift 15' boom to the loader bucket to lift, and set trusses on the shop I built at my old house. The trusses were only ~200#, and I couldnt curl them at all. But lift was no problem.

 

[gladehound]

I am using an auxiliary pump that will be added to the front of my tractor. Should I put a pressure relief before the valve? I hate to keep cluttering up this thread but it has so much good info and such great advice. I will start another one if you all think I should.

I've give my 2 cents but I hope someone who is more qualified answers your question. I've never set up a hydraulic system.

That being said, as long as you have an appropriately set relief in the system you should be fine. Lots of hydraulic systems have only one relief. Typically a tractor has a relief for the main system and when you add a loader it has it's own relief on the valve. My only concern with relying on a loader valve relief for a PTO pump is that it might not be sized large enough to handle the flow. If it's not, pressure could still increase even if it's open. So check that out. Makes sure the relief can flow the full output of the pump.

 

[davedj1]

I've give my 2 cents but I hope someone who is more qualified answers your question. I've never set up a hydraulic system.

That being said, as long as you have an appropriately set relief in the system you should be fine. Lots of hydraulic systems have only one relief. Typically a tractor has a relief for the main system and when you add a loader it has it's own relief on the valve. My only concern with relying on a loader valve relief for a PTO pump is that it might not be sized large enough to handle the flow. If it's not, pressure could still increase even if it's open. So check that out. Makes sure the relief can flow the full output of the pump.

Very good info, thank you

 

[Fallon]

All these calculations are missing one thing... The loader might not be the weak spot. There is a good chance your maximum loader lift capacity is actually based on your front axle or front tires. Personally I'd much rather go into relief, or blow a hose than bust my front axle. Blowing a tire with a heavy load could easily result in rolling the whole machine in many circumstances too.