Conversion Factor for 3PH load capacity

[BXpanded]

Quote:
Originally Posted by dodge man
I'll jump in here, and say what I think the problem is. People are thinking of the 3 point hitch like a tettor totter.

Someone correct me if I'm wrong.

__________________

Well I wont be the one to correct you....because you're right

But someone correct me if I'm wrong but isn't it spelled TEETOR TOTTOR

Sorry guys. I agree with the parallelogram concept (also an Engineer) but I think it's spelled Teeter Totter.

 

[AndyMA]

Sorry guys. I agree with the parallelogram concept (also an Engineer) but I think it's spelled Teeter Totter.

Teeter Totter See Seesaw - Wikipedia, the free encyclopedia

 

[SPYDERLK]

I just read the entire 7 pages of this post. Basically all of what SPYDERLK says is correct. He is a trained and practicing mechanical engineer as am I. Statics, Dynamics, Kinematics and other elements of mechanical engineering and Physics explain how mechanical things work. What many of you are trying to do is force a simple explanation on a problem that was solved long ago. On this site there is much false information conveyed particularly in the area of electricity/electronics. I happen to have over 35 years experience as a dual degreed engineer and there are many things written here that just make my hair stand up. I usually only jump in when I see a real dangerous situation being created in the electric world. I commend SPYDERLK for his tenacity and patience in carrying on with this thread,

Andy

No credit to me????

An Hydraulic top link,
some sensors,
an adaptive algorithm,
electric controlled valves on to the top link.
(All/most of this has been done for the electric/electronic versions of self leveling loaders)

It seems the 100% goal could be accomplished with a little electronics that lets the top link out at a rate that is some function of the rate of lifting.
Not a faux parallelogram, but doing the same thing - functionally.
Heck, anyone for 105% ? 110% ? just change a variable (or two).

Reg, Intriging idea. It wont work tho. Bummer. To test, extrapolate on a lift, from the ground, of weight equalling lift eye force but centered some distance behind the eyes. Be sure that you start with an imperfectly dimensioned //ogram.

Andy...LD1, please introduce some insights. I havnt got time to sweat this thru right now [long workdays mid week], but my initial gut reaction is you can do >100% [unleveled] with a passive imperfect // having lift arms shorter than toplink, but w/o sequential actions [cheating] you cant get even 100% with an active one no matter what you do because the active link is using Energy.
larry.

 

[slowzuki]

You guys are funny. Spider has the answer. The engineering term is instant centre and the field of dynamics is 4 bar linkages..

If your 3 ph lower arms and top link are parallel and the same length, any attachment will have no rotation during the lift. The hitch can lift its ball end rating 10 feet out in this config. The tractor wouldn't have enough weight to do it though and the top link may rip out of the tractor though. The linkage has an infinite instant centre.

If you shorten the top link, you will cause a rotation during lift, and the top link will have a greater angle than the lower arms, so a component of the tension in the top link will now have to be carried as a vertical force in the bottom arms. This reduces the vertical lift capacity. The instant centre becomes the point where the lines of the hitch intersect, somewhere towards the front of the tractor.

For fun put a really long top link into the pic can you could lift a massive load, but it would crush lower arms in compression. The instant centre would be to the rear of the tractor.

This is probably beyond most folks on here unless we have some stock car racers?

 

[SPYDERLK]

I have had the opportunity to do measurements at points on a boompole using a Dillon force gage. I used the 7520 as the test platform and turned hyd pressure down to 1000PSI so I wouldnt bend the boompole. I did 2 setups:
1]

Used a chain in place of the toplink to get the lift ratio as close to 1 as possible. Best I could do was 3/4 - - 24" lift at the eyes and 32" at the end loop of pole 108" out from the eyes.​

2]

Used the toplink adjusted to max length. The best lift ratio I could get at the pole end was 0.61​

The lift forces I measured in the 1st case were 1710# at the eyes, 1160 @ 56", and 980 @ 108".

The lift forces in the second case were 1700, 1200, 880 respectively.

,,,I believe the anomalies shown are due to my neglect in assuring that the lift was always done at the same eye height. The force available at the eyes varies some with height.

I did one more experiment in case 2 by successively shortening the toplink 3 turns at a time. Here I did take care to hold eye height pretty close to constant. The force measurements at 108"were 880, 850, 800, 760, 725.

While I had the force gage I took some loader measurements too. I found that it took 700PSI to get the loader to rise with the Tilt-tatch and bucket -- and 800PSI to get it to full height. I then turned the pressure up to 3000 as I normally keep it set. Center bucket force was 5100# at 1 foot lift height. ... Quite a surprise since this is 26" forward of the pins.​

 

[Reg]

5 1/2, nearly 6 years later....
Do you REALLY think anyone still CARES about this ?

The answer is whatever load whoever is on whichever tractor feels as the pucker factor limit when they will try to carry it across whatever terrain they plan to go over.
Stability and operator judgement (or lack of it) is almost certainly going to rule, not 3PH geometry.

The number doesn't matter, in most cases the weight of the object is unknown - you can either lift it or you can't, once lifted you will either feel OK about moving it to where it has to go or you will have the good sense to put it down.

 

[LD1]

I care:laughing:

Glad you got to do some testing. Certainly some anomalies. Like case 1 that lifts more at 108" than case 2, but the results are reversed at 56"?

I am surprised that 75% is the closest you could come to parallel. I would be interested in seeing the difference it makes just changing top hole location. IE: short link in bottom hole (tractor side) vs long link in top hole.

 

[SPYDERLK]

I care:laughing:

Glad you got to do some testing. Certainly some anomalies. Like case 1 that lifts more at 108" than case 2, but the results are reversed at 56"?

I am surprised that 75% is the closest you could come to parallel. I would be interested in seeing the difference it makes just changing top hole location. IE: short link in bottom hole (tractor side) vs long link in top hole.

Yeah, the tractor is poorly set up for max lift force. The swing point of the toplink is about a foot behind the liiftarm chassis pivots. I used the highest toplink pivot and with the chain hookup lowered the connection point on the implement to achieve the 75%. The chain was very springy [wrt the actual toplink which gave perceptible rigidity to the setup even 9' out] - another error source in comparison. If Id felt comfortable with the time involved I would have rigged an alternate lower hole for connection on the implement and used the toplink. That would have eliminated the springiness causing affective geometry changes on the fly.

Its too bad I couldnt try all variations, but many time conflicts arise promptly when you park a working tractor and start making iterative changes this time of year on a farm. Unfortunately, this is a last minute thing as I lose access to the force gage next week. :confused3:

 

[CalG]

I feel that 98% of this thread missed the OP's question.
The hydraulic lift arms of a 3PH have only a certain amount of force available. Either the limits of fluid pressure X piston area X mechanical leverage, or the failure of the lift arms or rock shaft.
Hopefully, the hydraulics (safety bypass) will yield before metal fails.

With that, a lifting arm with a limited amount of force can only be expected to produce a certain value of force at the business end. It could be a measure of pound feet, or newton meters or whatever. BUT, there is a fixed maximum. If the load center of mass is placed more distant from the neutral force, the total amount of weight that can be lifted will be decreased. ft X lbs remains a constant. In the same way, if the load were brought inside of the lifting eyes of the lifting links, a greater weight could be elevated. (even if not so high ;-)

IF one knew the lift arm lengths, and all the details of hydraulic pressures and mechanical ratios within the 3PH mechanics of two tractors to be compared, a simple formula could be derived that could correlate the two lifting capacities.

Without those details, all one can do is approximate.

All this talk of //motion linkages is obfuscation. Even if the motion ratios can be directly compared to the LIFT capacity.

 

[PILOON]

If the specs were 2000lbs at 1 ft then 1000 at 2 ft or again 500 at 4 ft.
The math is not all that difficult.
You convert to foot pounds; 2000 X 1ft= 2000 ft lbs
If load is then at 3 ft, 2000/3=666.6 lbs.@ 3ft.