Lift Capacity @ 24" for SubCompacts

[SPYDERLK]

Raising it HIGHER does NOT require more force. In fact, the very geometry you guys are going on about makes it EASIER to raise the ball as it goes higher than the ball eyes. Why? Because as the ball goes higher than the pins, the 3pt arms bottom attachment point starts to take some of the weight of the object. So there is LESS mass for the hydraulics to lift at the higher points. Its the LOWEST point that requires the most lift force because its the only position in which the hydraulics are lifting the entire mass of the object. And again, the toplink has nothing to do with it other than changing the angles of attack.

Perhaps we should revisit a previous thread where a lot of effort went into getting the truth out:
http://www.tractorbynet.com/forums/buying-pricing-comparisons/145738-conversion-factor-3-point-hitch.html

 

[tsteahr]

So, after all that (which totally lost me), Have I purchased a tractor that is being outperformed by every other model

Not at all. I agree with LD1. If the hitch can lift all the implements that are appropriately sized for the tractor (the heaviest I can think of are a 48" bush hog or a BX42 chipper, both about 450lbs) then it's sized correctly for the tractor.

In the real word I don't there there is much difference between any of the SCUTs in terms actual capabilities. I think all the SCUTs you listed are very similar. I think it's foolish to think any one is going to significantly outwork, out lift, out dig, out mow, you name it, than another.

 

[tsteahr]

Perhaps we should revisit a previous thread where a lot of effort went into getting the truth out:
http://www.tractorbynet.com/forums/buying-pricing-comparisons/145738-conversion-factor-3-point-hitch.html

Wow Larry :shocked:,

Excellent thread! I give you and LD1 credit for getting through that. That was brutal. I'm glad I did not have to type out all that explanation. You only have some many of these debates in you before you run out of steam.

Tom

 

[arrabil]

You know, I'll assume I don't know squat. So educate me..... After reading your linked thread I have the exact same concern as I did beforehand:

As the object is lifted and its weight begins to be transferred to the lower 3pt mount at the tractor (D), doesn't the effective/visible weight seen by the hydraulics go down?

 

[tsteahr]

You know, I'll assume I don't know squat. So educate me..... After reading your linked thread I have the exact same concern as I did beforehand:

As the object is lifted and its weight begins to be transferred to the lower 3pt mount at the tractor (D), doesn't the effective/visible weight seen by the hydraulics go down?

A fundamental principal of a truss or pinned linkage system is that force is only transferred in line with the link, from pin to pin. So when there is tension in the top link and the load is lifted, the tension in the top link is applying some downward force onto the implement, and in turn onto the lower link at point C. If the links are parallel, this added force is exactly the same as the weight transferred to point D by the lower link. Therefore weight seen by the hydraulics remains the same.

But when the system is in the B' configuration and the top link is at a steeper angle than the lower link, the downward force applied by the top link tension is greater than the load transferred to point D by the lower link. As the load is lifted this disparity between the increasing tension in the top link and the load transferred onto D increases. Hence the weight seen by the hydraulics goes up. What you gain for this increased increase in weight seen by the hydraulics is greater lift height of the load. (Nothing lost, nothing gained in a linkage system, just trade-offs of leverage, forces and displacements).

Imagion the B configuration where the links are parallel and horizontal. The top link needs to have sufficient tension to prevent the load from pivoting around the lower link ball eye so everything remains in balance. The pin A at the top of the load has to see a horizontal force. If the top link is no longer horizontal the load still needs that same horizontal force stay balanced. The only way to keep the same horizontal force at the pin if it is not horizontal is to increase the tension in the top link. But this non horizontal top link now adds a downward force component. The amount of this angle determines how much downward force is added.

I honestly don't know if I am helping this or just adding more confusion. If I could draw pictures on a chalkboard it would make this easier...

 

[arrabil]

there is tension in the top link and the load is lifted, the tension in the top link is applying some downward force onto the implement

How can the toplink apply downward force? Where does this force come from? The object acts on the toplink, not the other way around. Either the object is pulling on the toplink, tension. Or the object is pushing on the toplink, compression. How is it possible for the toplink to act on anything?

EDIT: This adds to my original question.... as the object is raised and the weight of the object is transferred to BOTH point D and point B/B' is not the effective weight seen by the hydraulics lower?

 

[tsteahr]

How can the toplink apply downward force? Where does this force come from? The object acts on the toplink, not the other way around. Either the object is pulling on the toplink, tension. Or the object is pushing on the toplink, compression. How is it possible for the toplink to act on anything?

Imagine yourself standing on the implement holding on to the top pin. The top link is connected to the tractor at a point lower than the pin you are holding. The top link is in tension, otherwise you and the implement would fall backwards. If the top link is in tension and point down, it's applying a force onto you partly in the horizontal direction and partly in the downward direction. Your legs have to resist this load (compression). This downward load goes through your feet, onto the bottom of the implement and onto the lower link eyes.

So the object acts on the top link and vise versa. This is how we have equilibrium.

 

[arrabil]

I cannot imagine any physics professor accepting your explanation of Newton's Third Law. In fact you've got it backwards.... if the link is in tension, it is applying a force away from the object as its the object that is applying a downward force on the toplink to put it in tension in the first place. Gravity is what my feet are resisting and I'm pulling on the toplink as gravity works on me. The toplink then resists this in the direction of the tractor to maintain equilibrium.

Either way, I understand your point on Newton's 3rd. But I'd like you to address my question on the effective weight seen by the hydraulics as the weight is transferred to points on the tractor and away from points lifted by the hitch.

 

[tsteahr]

How can the toplink apply downward force? Where does this force come from? The object acts on the toplink, not the other way around. Either the object is pulling on the toplink, tension. Or the object is pushing on the toplink, compression. How is it possible for the toplink to act on anything?

EDIT: This adds to my original question.... as the object is raised and the weight of the object is transferred to BOTH point D and point B/B' is not the effective weight seen by the hydraulics lower?

OK. If a force is applied at a 45 degree angle toward the ground there is a both a horizontal component and a vertical component to this force. Each component happens to be 0.707 [sine(45)] of the total force.

If you hold a top link in your hands and I pull on it at a angle 45degrees below horizontal with a force of 100lbs, you will feel 70.7lbs of force straight down your legs. In addition you will need to have someone hold onto your shoulders and resist 70.7lbs of horizontal force.

This is what is meant when we talk about resolving forces into components.

Time for me to hit the bed...

 

[arrabil]

Again, I totally understand Newton's 3rd but I don't see how it pertains to what I'm asking.