Check My Assumptions and Calculations on Winch

[Gordon Gould]

I was looking at a thread by dstig1 on his PTO and winch and became
interested in calculating what my Farmi Winch and L3010 could do.
Are these numbers reasonable ??

L3010 PTO = 25 hp @ 540 RPM (engine @ 2700RPM) Kubota Spec

Torque at PTO shaft = ( 25 hp X 5250) / 540 RPM = 243 ft-lbs

I run my winch at 1200 to 1800 engine RPM. PTO torque should still
be 243 ft-lbs or more due to diesel torque curve being fairly flat or higher
at lower RPM.

Winch has a reduction gear. Input 14 teeth, Drum shaft 66 teeth.

Drum Shaft Torque = 243 ft-lbs X (66 / 14 ) = 1145 ft-lbs

Drum Diameter when full of cable = 8" ( Radius = 4" or .33 ft )
Drum Diameter when cable all strung out = 4" ( Radius = 2" or .167 ft )

Ignoring Clutch and Losses:
Cable Pull Full Drum = 1145 ft-lbs / .33 ft = 3470 lbs
Cable Pull Empty Drum = 1145 / .167 ft = 6856 lbs

Farmi sets clutch at 6400 lbs ( I assume with empty drum )

Clutch slips at 6400 lbs X .167 ft = 1068 ft-lbs on Drum Shaft

Actual Max Full Drum Cable Pull = 1068 ft-lbs / .33 ft = 3236 lbs
Actual Max Empty Drum Cable Pull = 1068 ft-lbs / .167 ft = 6400 lbs

Am I on solid ground here ??? Thanks

 

[Ford tractor]

Looks ok to me:thumbsup:, but all you needed to know is that Farmi sets the clutch at 6400#. If it's slipping, you make more torque that that, and if the engine bogs you make less.

Why do you need to delve deeper?

 

[Gordon Gould]

I guess I just find it interesting how well theory matches up with real life.
Plus I learned some stuff.
I now know my tractor should have enough torque to slip the Farmi clutch,
but just barely. So it's probably a good match. I can use all the power I got.
I give my dealer the credit for that.
The biggest thing I learned though is how much the pulling force
varies. I knew I had less pull in close than out far but I didnt realize how
much less.
By taking some measurements and doing the calculation I know I have about
6000 lbs pull at 150 ft of cable and only about 3000 lbs pull at 20 ft.
To me thats worth knowing.

 

[DonnieP]

Get a snatch block and you can bring that 3000 up to 6000.

Donnie

 

[Baby Grand]

You could always check your hand calculation by a little empirical delving: see what it will dead lift. Yet another use for the snatch block: run the cable out straight and then down 90 degrees using the snatch block. Just make sure the cable angle causes the blade to dig in. Get a pallet and load it up with something you know the weight of - water tank, bricks, log, etc. Keep adding weight until the clutch starts to slip.

 

[Gordon Gould]

Some interesting ideas. Thanks.
Actually I have 3 blocks and 3 five foot web straps w/ looped ends I carry
with me all the time. My wood lot is very hilly and my tractor is small. I have to keep it pretty much straight up and down a slope so I use the blocks to
snake the cable around as needed and to avoid snags or damaging good trees. Sometimes I hang a block about 5' off the ground to lift my log
over an unavoidable snag. They are very handy.
I realize that a lot of the above is pretty academic because 3000 lb pull
is usually plenty for a 5000 lb tractor but I still find it interesting. I wish
I knew enough to do that calculation 9 years ago when I got the winch.
I have learned alot on TBN - Thanks

gg

 

[Dead Horse]

properly rigged these winches can exert some serious leverage and get a lot of work done.

I get in the "pay REAL close attention to what you are doing territory" when the winch pulling capacity exceeds the weight of the tractor.

Sounds like the farmi you have is a 351.

I have a 601 that I recently rebuilt. It has made the rounds with previous owners here on TBN. Awesome winch.

Gotta remember that starting friction is always greater than sliding friction. That little physics lesson has come in handy in my experiences.

One thing about your calculation that has me scratching my head....... I thought torque = hp @ 5250 rpm.

 

[Gordon Gould]

You are correct.

HP = ( Torque X RPM ) / 5250

So if RPM = 5250 then HP would equal torque.

HP = ( torque X 5250 ) / 5250

At any other RPM value HP does not equal torque.

I algebraicly changed the formula around to get

torque = ( HP X 5250 ) / RPM

and plugged in 25 PTO hp at 540 PTO RPM to get 243 ft-lbs PTO torque.

 

[dstig1]

Interesting. I guess my setup is pretty similar to yours, give-or-take.

The point that you need to remember for pulling loads is that the load generates a frictional resistance that depends on only 2 things: 1. the weight of the load and 2. the coefficient of friction of the load on the surface. Now there are 2 coefficients here - static and moving. The static one is always higher which is a main reason it is harder to start a pull than to keep one moving. If you are pulling on level ground, that is really the only force you are pulling against, so if it is a big log that is near your limits, it pays for it to be far away to get it moving, but then don't stop until it is home...

Of course there are other variables here. Up slope or down slope is a biggie. Using any additional leverage like a block and tackle or snatch block (in certain types of pulls where you double back to the tractor) would be the other, though I doubt that is common in skidding winch use.

Of course calcualting this in the field is beyond silly....

-Dave