You need balast or you will trash your front axle!!!! really?

[jenkinsph]

Exactly! The calculation is all about weight and leverage, doesn't matter if it is a tractor or seesaw. The fact that the vertical changes the horizontal on your tractor is merely an implementation detail.

Yes, a fork lift with the mast set plumb would not change the loading as it is raised. A fel raises its load in an arc and moves the load rearward as it rises. It still needs to be calculated at the lowest starting point to make sense as you need to make the numbers work from start to finish.

 

[ovrszd]

Yes, a fork lift with the mast set plumb would not change the loading as it is raised. A fel raises its load in an arc and moves the load rearward as it rises. It still needs to be calculated at the lowest starting point to make sense as you need to make the numbers work from start to finish.

I agree with this theory. Not to doubt, just filling in the blanks in my empty theoretical mind. Isn't the farthest point of the arc from the front axle a few feet off the ground? Doesn't the bucket get closer to the tractor when it's sitting on the ground than up a little??

 

[sd455dan]

Some of these guys are having enough trouble understanding the static loading. Dynamic loads are a whole new ball game.

If that doesn't cloud things enough, lets also Add in efficiency in static loads?????

I always thought (efficiency) was used in dynamic calculations of work/time
not static load equations??:confused3:

 

[jenkinsph]

I agree with this theory. Not to doubt, just filling in the blanks in my empty theoretical mind. Isn't the farthest point of the arc from the front axle a few feet off the ground? Doesn't the bucket get closer to the tractor when it's sitting on the ground than up a little??

Yes if the bucket is below horizontal mounting of the pins on the loader arm. So you are correct. Raising the load you would have to meet this requirement as you raise the fel through this arc.

 

[jenkinsph]

I am sure that some would think that having the fel bucket close to the axle would be best. Anyone who has to load a dump truck knows how important dump clearance is too. You need clearance between the front end to prevent bumping into the side of the truck.

 

[Snowback]

Yes. It also adds lateral leverage if you're not on completely flat ground to tip you over sideways.
Hey, speaking of tipping over sideways have we started arguing about the role of the front axle pivoting yet?!

Great example of front pivot doing its thing when not enough counter weight is used. It's a fun short video to watch at this link: https://www.youtube.com/watch?v=mRus_-ipbUo

 

[CobyRupert]

Yes, a fork lift with the mast set plumb would not change the loading as it is raised.

Interesting.
...but as soon as you move the forklift backwards, doesn't Newton's First law say you're much more likely to tip the fork truck off it's rear wheels (that is: the horizontal force required to move the raised load backwards has a torque effect about the front axle that is multiplied by this raised height?)

 

[s219]

I know that a lot of you want to link the vertical position of the front bucket load into this, but all that does is add another layer that obscures the pure physics. Generally, when deriving the equations you want to keep driving things simpler and simpler, not get more complex.

An equation I posted back in #39, was:

F * LF = R * LR

This equation has to hold in order for no additional load to be applied to the front axle. In other words, you can think of this as a way to calculate the required rear counterweight so that no added load is placed on the front axle.

Here:

F is the load on the front loader
LF is the horizontal distance from the front loader's load to the rear axle
R is the load on the three point
LR is the horizontal distance from the three point's load to the rear axle

That tells us that the rear counterbalance load must be:

R = (F * LF)/LR

So that gets it down to forces and horizontal distances, and you cannot get it simpler than that.

Now, of course LF is geometrically related to the angle of the loader, so I could rewrite it as:

LF = LA + R * cos(theta)

Where: LA is the horizontal length from the rear axle to the front loader arm pivot, R is the "radius" that the front load arcs through, and theta is the angle from horizontal. With that, the equation would become:

R = (F * (LA + R * cos(theta)))/LR

If you instead want this in terms of the height of the bucket load H, it becomes:

R = (F * (LA +H /tan(theta)))/LR

All of these equations give the same result, just using different variables. But we had to pull geometry and complexity into this to express it in terms of something other than the horizontal lever arm. Complexity is the enemy of fundamental understanding. If you require complexity to understand the physics, you blew it!

Also note in this case we can use a single variable of horizontal distance, LF. But if we want to rework the equation to get away from that most fundamental form, we now back up to something that requires three variables, LA, vertical distance (H), and angle from horizontal (theta). We'll never be able to make this depend purely on the vertical distance, because it's not in the physics. If you want this to depend purely on a single length variable, that will have to be horizontal distance LF.

 

[s219]

I should add, in cases when using statics equations and summing moments, you should always look at the problem so that you are visualizing the lever arms perpendicular to the forces. Always. So in the case where all our loads come from gravity aiming straight down vertically, the lever arms are all going to be horizontal.

A good physicist can look at this problem and in their mind see those horizontal lever arms superimposed over the more complicated tractor. It's almost something that flashes in front of your eyes. What you are doing is immediately and viscerally simplifying the problem in front of you.

I think farmers, lumberjacks, riggers, and other practical folks who incorporate physics into their work (whether they know it or not) are doing the same thing without the equations or the physics. They can look at a practical problem and know the physics.

 

[CalG]

I should add, in cases when using statics equations and summing moments, you should always look at the problem so that you are visualizing the lever arms perpendicular to the forces. Always. So in the case where all our loads come from gravity aiming straight down vertically, the lever arms are all going to be horizontal.

A good physicist can look at this problem and in their mind see those horizontal lever arms superimposed over the more complicated tractor. It's almost something that flashes in front of your eyes. What you are doing is immediately and viscerally simplifying the problem in front of you.

I think farmers, lumberjacks, riggers, and other practical folks who incorporate physics into their work (whether they know it or not) are doing the same thing without the equations or the physics. They can look at a practical problem and know the physics.

Well put s219!

All forces (loads if you will) can be resolved into equivalent horizontal and vertical components. A start towards understanding a system through Vector Analysis.
Cranes and gin poles lift sizable weights without a lot of counterbalance by directing the lions share of the "tipping moment" into a vertical component.

The arc of a loader arm moving the CoG of the filled bucket is an unnecessary complication. The masted fork lift is a perfect example of why height should not enter into the original topic discussion. It may lead to other aspects however. The inertia aspect of moving off with a high load is an ENTIRELY different discussion. Considering the way this thread has gone, I suggest NOT going into that. ;-)