3 Point hitch upper link

[CalG]

I guess not.
Somehow I just can't get past the fact that without a top link, my rotary cutter sits on the back wheel no matter how hard the lift arms are pulling upwards. I guess it's just magic that with a top link, the rear end levitates and *checks notes* apparently puts all of the rear end weight back on the lower arms? Perhaps my understanding of vector forces, that the tension pulling diagonally upwards equaling an upward pull plus a horizontal pull... and that an upward pull is typically known as "lifting"... is wrong?
I guess I learn something new every day!

Consider

What if....

That "top link" where fixed to the tractor at a position BELOW the lower lifting arms. and extended out to attach to the mower at the tail wheel.

Still "lifting"? or just countering a moment.

or,

Stand that mower on it's front pins with the entire body vertical above. all in balance, hands off!

No top link required at all to lift the very same mower deck.

Go figure.

 

[SPYDERLK]

Guys and Gals (if any)

The many comments on this thread appear to have failed in one aspect. We have neglected to give significance to the vital aspect for resolving the forces on the top link, in that ALL THE LIFTING IS DONE BY THE UPPER LIFT ARMS!. You know, the pair of arms fixed to the rock shaft powered by a hydraulic piston under your seat.

All the other system element forces are due to the eccentricity of the load attached to the lower lift arms that are acted on by the side links.

The top link is only an anti- torque link, to resist the turning moment of the eccentric load around the far ends of the lower lifting arms. It can do no LIFTING , with ball swivels at each end. (A hydraulic top link could provide a vertical component to lift a load, but then it would be an actuator, not a link ;-)

The forces acting on the top link are measured in pound feet. (torque)
The loads seen by the top link are measured in pounds. (the feet "drop out" based on geometry)

Clear as mud , right? ;-)

I can explain it for you, but I can't understand it for you. ;-)

The force at the balls on the lift arms, as opposed to lift links, is what is important. The inward/outward force of the cantilevered implement is important also, and constant with a //ogram. No real point in resolving it into a Torque. It all just resolves into forces at angles and the resultant force in the direction of interest.
No toplink, hydraulic or not, will ever react to cause net lift. Rather a lift countered by an equal negative lift in the lower elements. However a hydraulic link can act to cause a net lift by virtue of utilizing its added energy source. An actuator as you say.

 

[Runner]

I would so much love to see a demonstration, whereby someone would install a scale between the top link and an attachment of known weight to demonstrate the #'s we are coming up with. You would think that, as long as three-point hitches have been in use, such a demonstration would exist, but I haven't been able to find it on the internet.

 

[Chewwy]

Consider

What if....

That "top link" where fixed to the tractor at a position BELOW the lower lifting arms. and extended out to attach to the mower at the tail wheel.

Still "lifting"? or just countering a moment.

or,

Stand that mower on it's front pins with the entire body vertical above. all in balance, hands off!

No top link required at all to lift the very same mower deck.

Go figure.

.
In the first example, the top link will be exerting force in both the x and y direction, and in actuallity some, albeit smaller force, in the z direction. In this example the top link would be in compression to provide those forces.

In the typical configuration with the top link positioned above the lower lifting arms, the link would be in tension to provide the forces in the x, y, and z direction. Call it lifting, pushing, resisting the moment, whatever. It still exerts a force in those directions.

In the second example above, clearly the top link is not needed since, being in “perfect” balance there is no force in those 3 directions.

But in reality, if you were to use the lower arms to actually lift, it would no longer be in perfect balance. Since the lower arms rotate on a pivot point there would be some movement either toward the rear or front direction and it’s going to fall over without the restraint provided by the top link.

 

[CalG]

{snip}

But in reality, if you were to use the lower arms to actually lift, it would no longer be in perfect balance. Since the lower arms rotate on a pivot point there would be some movement either toward the rear or front direction and it’s going to fall over without the restraint provided by the top link.

Exactly

The top link ONLY resists the rotation of the implement. around the lower lift arm balls.

Replace those balls with flat mounting flanges and bolt the implement to them, and again, no top link required.

There is even a name for such a tool lift in the tractor world , it is called a SLEEVE HITCH.

 

[SPYDERLK]

One implement I find could be hard on a top link is long ones like brush cutters. I actually sheared a few bolts on my NH top link mount. That’s a lot of weight bouncing around.

Yeah. I have one. As I recall those are 1/2" Gr5 bolts. After failure I replaced mine with Gr8 tightened to full Gr8 torque spec. Its been trouble free since.

 

[LouNY]

Exactly

The top link ONLY resists the rotation of the implement. around the lower lift arm balls.

Replace those balls with flat mounting flanges and bolt the implement to them, and again, no top link required.

There is even a name for such a tool lift in the tractor world , it is called a SLEEVE HITCH.

Garden tractor world,
of course there was an excellent 2 point hitch system the IH Fast Hitch that came out with the hundred series tractors, I believe there was even a one version on the 100 and 200 models.

 

[Chewwy]

Exactly

The top link ONLY resists the rotation of the implement. around the lower lift arm balls.
. . .

The resistance of motion around the lower lift arms is achieved by exerting force in both the x (horizontal) and y (verticle). Any force in the positive y direction (i.e., upward) is supporting some of the weight of the implement.

 

[CalG]

The resistance of motion around the lower lift arms is achieved by exerting force in both the x (horizontal) and y (verticle). Any force in the positive y direction (i.e., upward) is supporting some of the weight of the implement.

Any becomes None when the upper link is horizontal

 

[MoArk Willy]

I can explain it for you, but I can't understand it for you. ;-)

"If you can't explain it to a six year old then you don't understand it yourself"
Albert Einstein.