Sizing Farmi skidding winch for my 3720 Deere

[Gordon Gould]

There is a misconception on winch usage that I think should be cleared up.

The idea that using the lower pulley provides down pressure on the winch because the cable is pulling straight down on the top pulley is a common misunderstanding. When you look at it you say "that makes sense". But in reality the same force that is pulling straight down on the top pulley is also pulling straight up on the lower pulley. That means that the net vertical force on the winch from those two forces is zero.
The only force exerted on the winch by the cable is the cable tension at the point of exit. And it is in the direction of the exiting cable. All the internal cable forces cancel each other out. For example, the cable pulls straight up on the drum but it also pulls straight down on the top pulley with an equal force (Cable tension).

The only time you get a downward force on the winch is when the cable exits at a downward angle (ie from the top).

I have attached a paper written by Farmi which makes a statement about this. They recommend winching from the top pulley and skidding from the bottom pulley.

respectfully,
gg

 

[dstig1]

Second the advice to watch the cable (or the drum in my case as it is out and exposed in my old model). I try to watch the drum and quickly glance out to the log just to make sure things are moving properly and to see how far out I am.

RPMs will be tractor dependent. On mine I find I need to run it full throttle for decent pulling force, but then full throttle is right about the RPM specified for the PTO in my case.

I have also found that good technique is to start fast to get the log broke free and moving. I tend to pull hard right off the bat and then back off if I can. Or just leave it at full clutch for the bigger ones. Also helps to be braced against a stump or the feet/blade can keep digging in more and more if you have soft ground.

No lower block on mine either, so all pulls are from the top. It helps keep things up out of the dirt near the end a bit. I don't see a problem using the upper block...

 

[Dead Horse]

There is a misconception on winch usage that I think should be cleared up............

The only time you get a downward force on the winch is when the cable exits at a downward angle (ie from the top).

I have attached a paper written by Farmi which makes a statement about this. They recommend winching from the top pulley and skidding from the bottom pulley.

respectfully,
gg

Farmi offers the owners / operators manual for each model, on their web site.

Here they are: http://www.farmiwinch.com/index.php?option=com_rokdownloads&view=folder&Itemid=106

They are a nice, fairly complete documents describing safety, operations, assembly and maintenance of the winch. I highly recommend anyone who owns or is interested in a Farmi, go to the site and download the manual.

BTW, these manuals do not speak to the multiple physical forces present in various techniques of winching, except in a very general, poorly translated way. The JL 601 manual does recommend using the lower snatch block for heavy load winching.

While the manual(s) also state that the lower snatch block is useful for leaving the load attached to the cable and skidding out that way, it also states that dropping the choke chain into the notches on the frame and skidding that way is another technique.

In looking at the ratchet brake on the winch, it is obvious that the whole load (farmi says 4 logs worth) will be suspended/pulled from the ratchet brake mechanism in the winch if left attached to the cable and skidded out that way.

On my 601, (of which I am at least the third owner), the ratchet parts show significant wear and some deformation. I came to the conclusion that dropping the choke chains into the slots on the winch frame was a far better, less prone to a single point of failure, way to skid the load out. It allows the load to be spread across the base of the winch frame as well as it takes all the load off the cable, sliders, ratcher brake and winch.

Again, as to directional forces applied, including leverage, the manual is essentially silent.

I am intrigued by the subject and would like to hear the opinion of someone knowledgable (by trade or education) on the subject.

 

[Gordon Gould]

I am intrigued by the subject and would like to hear the opinion of someone knowledgable (by trade or education) on the subject.

I believe what I have said is correct. The source of my knowledge is through a fairly rigorous education in the field of physics. But it was a long time ago. If what I have said is incorrect I certainly want to know and will gladly admit my mistake.

I agree with everything you say. It is all good stuff except for the added down pressure when winching with the lower pulley.

gg

 

[Dead Horse]

I have to believe the angles involved have something to do with distributing the direction of force applied to the cable. I can certainly understand how the ingress angle and the egress angle of the cable on the lower snatch block could cancel each other out if they are exactly equal.

They would not generally be exactly equal though. Especially if one were winching a log up a grade or even on flat ground.

I do appreciate your providing your credentials as regards the matter, and I am SURE I can learn something from this discussion.

The thing I do believe about threading the cable through the lower block for a pull is that it does shift the pulling force from the top of the winch to the middle of it. I like that because it spreads the pulling force to all three links of the TPH, going from a tensile force on the top link (and mild compression force on the bottom links), to a compression force on the top link and tensile force on the lower links. The fulcrum point has been changed.

 

[KennedyDiesel]

FYI I did get my Farmi 351P last week. Weather did not allow us into the woods though.

Imatch connection will be a definite issue. The lower pins are spaced perfectly, but should be 2-3" further fwd. The upper link is way too high. Making a different upper link attach point would not be too difficult, BUT it will fall right in the middle of the plate that holds teh winch axle so deflection would be a concern. Thinking I'd have to make a long rail to keep from bending this plate OR try some sort of a bolt on configuration.

As for the top pulley versus bottom the way I see it is that if you use just the upper you will get max down force provided it is higher than the hook. If you add in the lower pulley you will decrease the downforce and apply the force as a compression force trying to bring the pulleys together. In other words the downforce is only affected by the point at which the cable leaves the machine. Now if you had a lower pulley that was not attached and say earth anchored, THEN you would get downward force.

At least that is what my limited education from the school of hard knocks tells me...

 

[Dead Horse]

I agree with you Kenny. good luck with the winch. Mine is an awesome tool........it does amazing things that I absolutely could not do with out it.

 

[BWSwede]

"The upper link is way too high. "

I believe Farmi did this on purpose. With the upper link set unusually high the top of the winch will pull back toward the tractor rather quickly and it doing so causes the blade to kick out. When the blade kicks out it supports the butts of the logs when transporting the logs back to the deck.

GG's explaination is correct.

The top pulley is for winching, the bottom pulling is for transporting. Farmi, or one of the other tractor skidding winch manufacturers, shows this on their promotional videos.

Blane
Farmi 501
Unimog 406

 

[Glen Watkins]

[/quote]GG's explaination is correct.

The top pulley is for winching, the bottom pulling is for transporting. Farmi, or one of the other tractor skidding winch manufacturers, shows this on their promotional videos.

Blane
Farmi 501
Unimog 406[/QUOTE]

A lot of good info here. The guy I bought my winch from showed me his cat.1 top link that was broke apart right around one of the balls! He said he thinks it was because he was pulling from the top pulley only. Makes sense because it looks like a lot of leverage can be applied to the link from there. might have been a cheap link but a good thing the link broke and not the back end of the tractor! Dealing with some serious forces here either way. I will be using both pulleys and I think I will add some length to my clutch rope so I can hide behind a big tree!

 

[Dead Horse]

Agreed, Glen. This is the point I was trying to make in my last description of the forces applied to the links, in a pull.