Why 4 Wheel Drive

[SPYDERLK]

[I didn't think about until I read the link on the drawbars, 4wd due to the torque is divided between 2 axles this also makes the tractor less likely to lift the front end.] That seems to make some sense. I only throught about the added weight. So that would be another plus for 4wd.

Does a link state this or is this a deduction? Off the top of my head --Other than the added front weight there would be no difference if the pull point were the same. Summed torque effectively moves to the rear as the fronts unload.
larry

 

[SPYDERLK]

OK so you have a better understanding of physics that Penn State's Ag Department which is putting out safety misinformation? You also seem to know more than probably every farmer I've ever known.

You know it's not about being right or wrong, I come here to learn and share knowledge if I can. If you want to say others are wrong and don't understand, why don't you show us something other than "your understanding of physics". Others here have been good enough to put links to information that supports there point. All you have done is put up at times gobbldygook, and now you say something that does not agree with you is misinformation. No one with a real understanding of physics would say a rotating shaft of any kind, axle or not puts out a forward force, shaft are for torque. [Not only did I take some physics, but I have a job that I actually apply physics in on a regular basis.

You have an inquiring nature, why don't you connect a tractor to something and see for yourself. Or at the very least show us where you are getting your information from.

Look up the Nebraska test data on some tractors. How could a tractor have a drawbar pull almost equal to it's weight if the drawbar didn't keep it from going over? That's pounds of pulling force, not pulling a load on wheels that once moving only takes a few HP to keep the load moving. [Going by what you claim the only force counter acting the rotation is the weight over the front axle which on most tractors is 40% or less, any weight on the rear axle would be trying to lift the front end.]

Im glad you have training in physics. Lets use it. 40% on front axle - radius of rear wheels less than 40% of wheelbase -traction coefficient of 1 - pull point straight back at axle level - level ground - no acceleration. What do you get?

Once I had a high school Physics Prof who was teaching my daughter tell me a motorcycle could stop faster/shorter than a truck because it was lighter. See the problem?
larry

 

[JasG]

Im glad you have training in physics. Lets use it. 40% on front axle - radius of rear wheels less than 40% of wheelbase -traction coefficient of 1 - pull point straight back at axle level - level ground - no acceleration. What do you get?

Once I had a high school Physics Prof who was teaching my daughter tell me a motorcycle could stop faster/shorter than a truck because it was lighter. See the problem?
larry

An object of less mass (lighter) takes less energy to stop. So I would say the high school physics professor is correct under the same condtions from the same speed most of the time a motorcycle will stop faster than a truck. I say most of the time because you can set up examples of super light truck vs heavy bike that would be different, in gereral though that statement is true. Your question is what I meant by gobbldygook. I have no idea what you are looking for, so why don't you explain it?


"Does a link state this or is this a deduction? Off the top of my head --Other than the added front weight there would be no difference if the pull point were the same. Summed torque effectively moves to the rear as the fronts unload."

Also if you had read the paper sited it did explain that once the wheels were off the ground, it was the same as a 2wd tractor except for the added weight of the drive. The torque split was only as long as the front wheels were pulling. So this shows me that you didn't even look at the paper, yet you totally dismissed it.

Like I asked before, site where you are getting your information from. Instead of being so defensive and dismissive. So far your comments show that you think your veiw is correct and anything that goes against it you aren't even willing to look at. Yes at this point I see the probelm clearly now, you have no idea what you are speaking of. Your last statement shows this clearly. So until you can show something as to where you are getting your information I'm not going to respond futher to your posts.

 

[SPYDERLK]

An object of less mass (lighter) takes less energy to stop. So I would say the high school physics professor is correct under the same condtions from the same speed most of the time a motorcycle will stop faster than a truck. I say most of the time because you can set up examples of super light truck vs heavy bike that would be different, in gereral though that statement is true. Your question is what I meant by gobbldygook. I have no idea what you are looking for, so why don't you explain it?


["Does a link state this or is this a deduction? Off the top of my head --Other than the added front weight there would be no difference if the pull point were the same. Summed torque effectively moves to the rear as the fronts unload."]

Also if you had read the paper sited it did explain that once the wheels were off the ground, it was the same as a 2wd tractor except for the added weight of the drive. The torque split was only as long as the front wheels were pulling. So this shows me that you didn't even look at the paper, yet you totally dismissed it.

Like I asked before, site where you are getting your information from. Instead of being so defensive and dismissive. So far your comments show that you think your veiw is correct and anything that goes against it you aren't even willing to look at. Yes at this point I see the probelm clearly now, you have no idea what you are speaking of. Your last statement shows this clearly. So until you can show something as to where you are getting your information I'm not going to respond futher to your posts.

OK, so I asked an honest question because I didnt see that in the link and you ridicule even tho my [brief hypothetical] included the same consideration: "Four-wheel drive tractors are less susceptible to the rear axle torque hazard than two-wheel drive tractors because torque is applied to both the front and rear axles and tires. Also, more weight is carried on the front axle, moving the CG forward. These features lessen the tendency of the front of four-wheeled drive tractors to lift off the ground. But, once the front end does lift, there is little practical difference between two- and four-wheeled drive tractors." I wasnt sure what link it was in so it seemed easier to ask than peruse each. Thanks for pointing it out in such good form.

I am not getting my information from a site. I learned it previously so it is in my head. Your answer to the motor cycle vs truck stopping gets a 10%. The energys are surely different but so is the rate at which that energy can be subtracted to reach a stop - other pertinent things being equal the rates are exactly proportional to mass. The stopping distance does not hinge on the weight but on brake capacity and tire friction coefficient. With= tire coefficient and controllable brakes of adequate power to bring them to a skid they would stop exactly the same if both operators were equal skill.
larry

 

[piller]

OK, I'm not taking sides here, I did go to the link provided by jagyzf, there is some good info there, however I think there is at least one error.

In the section on drawbar leverage it talks about angle of pull, and shows a picture (figure 5) of a tractor and a tree stump. There appears to be a chain connected from the tractor drawbar that goes straight back horizontally to the tree stump. The text says that the angle of pull provided by the load is down and back, shown going to the base of the stump at ground level. I believe that when pulling on a chain that the angle of pull is directly in line with the chain, or in this case horizontal. Any thoughts on this?

 

[SPYDERLK]

OK, I'm not taking sides here, I did go to the link provided by jagyzf, there is some good info there, however I think there is at least one error.

In the section on drawbar leverage it talks about angle of pull, and shows a picture (figure 5) of a tractor and a tree stump. There appears to be a chain connected from the tractor drawbar that goes straight back horizontally to the tree stump. The text says that the angle of pull provided by the load is down and back, shown going to the base of the stump at ground level. I believe that when pulling on a chain that the angle of pull is directly in line with the chain, or in this case horizontal. Any thoughts on this?

Yes, I agree with you. I mentioned the same in post 78. There is a previous thread where it was discussed about a year ago.
larry

 

[EE_Bota]

I only really popped back on to mention that David Bradley is just one I found for sale on Ebay (in case anyone is interested)

I read the link about the stump pulling thing, and I did not see any problem with any of it except one of the line of pull diagrams. The first one looks funny to me, but the other two are quite reasonable in my opinion.

 

[jagyzf]

Now I'm not the sharpest tool in the shed and I don't pretend to be. I also agree Figure 5 doesn't seem right in that paper, but 6 and 7 do seem correct along with the rest of the document. Like I said I found it and it fit what I have had in class's on equipment safety. I also agree with JasG at times Spyderlk I can not follow what you are trying to explain at times. Which you may be the smartest guy on the planet, but if you come across in a way that 1) can't be understood, and 2) is to be so unwilling to explain why your point is correct you won't be of use to many people. You say you learned it and it's in your head. I work with engineer's everyday, all of them very smart and hardworking. Not one of them does everything from there head. They know where to find the correct formula, but unless it's one they use everyday they look it up. The electrical engineer's I have worked with carry "pocket" references just because of this. Not say you are wrong, but you are not in my mind explaining things very well and it at times conflicts with things I have learned over the years.

 

[SPYDERLK]

PLEASE explain this;
It might be geometry, it might be physics, it might be mechanics that I lack a good enough understanding of.
Just HOW can you set up a tractor to "actually be pulling down on the front end" ?

You hit it. You would have to set up a pull point below ground level!!! - Forward of the rears would be a help too. No sweat.
larry

The wheels apply force at the ground. If the load applies resistance above the ground you cant be pulling the front of the tractor down.
larry

Note that the description is regarding ground engaging implements. All of their resistance to motion is at or below ground level. So yes in that instance the front end is pushed down. The distance below ground the force is applied times the force applied by the tires at ground level is the net torque trying to rotate the tractor forward [front tip]. If the resisting force is at ground level there is no net torque. If above ground there is net torque trying to back tip the tractor. In each case these torques are proportional to the vertical distance from the level at which the tractor exerts horizontal force to the level at which the load exerts horizontal force.
larry

[[How do you figure that?]].

Nothing I said prevents a tractor pulling a load up a hill. The hill just lightens the front a bit more.

The tires apply force rearward and the axles apply the same force forward into the tractor body. Force resisting motion of the tractor [for acceleration or pulling a load] has effect based on where relative to the ground that force is applied. That resisting force is applied at the tractor Center of Mass [pretty high]for acceleration or when climbing hills. It is applied at the level of the hitch point when pulling a load at steady speed. Accel and/or a hill will still increase the tendency to tip back regardless of the hitch level because of the high COM.
larry

Obviously no, since the axles are the only connection of the tractor to the wheel, whose traction applies the push. Yes, the tractor tries to rotate backward about the axle. A pull point below the axle resists this and a pull point that is below the axle an amt = to the wheel radius will resist it completely. The drawbar not being this low does not counter it completely until the tractor rears up enuf to bring the pull point [bar end] down to ground level - long bars are pretty safe.
While the link has good info, the pull angle diagram on the stump is totally bogus and discussed in a previous thread.

There is a lot of misinfo out there. The most effective weapon is an inquiring nature and an understanding of physics.
larry

Does a link state this or is this a deduction? Off the top of my head --Other than the added front weight there would be no difference if the pull point were the same. Summed torque effectively moves to the rear as the fronts unload.
larry

Im glad you have training in physics. Lets use it. 40% on front axle - radius of rear wheels less than 40% of wheelbase -traction coefficient of 1 - pull point straight back at axle level - level ground - no acceleration. What do you get?

Once I had a high school Physics Prof who was teaching my daughter tell me a motorcycle could stop faster/shorter than a truck because it was lighter. See the problem?
larry

OK, so I asked an honest question because I didnt see that in the link and you ridicule even tho my [brief hypothetical] included the same consideration: "Four-wheel drive tractors are less susceptible to the rear axle torque hazard than two-wheel drive tractors because torque is applied to both the front and rear axles and tires. Also, more weight is carried on the front axle, moving the CG forward. These features lessen the tendency of the front of four-wheeled drive tractors to lift off the ground. But, once the front end does lift, there is little practical difference between two- and four-wheeled drive tractors." I wasnt sure what link it was in so it seemed easier to ask than peruse each. Thanks for pointing it out in such good form.

I am not getting my information from a site. I learned it previously so it is in my head. Your answer to the motor cycle vs truck stopping gets a 10%. The energys are surely different but so is the rate at which that energy can be subtracted to reach a stop - other pertinent things being equal the rates [at which energy can be subtracted] are exactly proportional to mass. The stopping distance does not hinge on the weight but on brake capacity and tire friction coefficient. With= tire coefficient and controllable brakes of adequate power to bring them to a skid they would stop exactly the same if both operators were equal skill.
larry

Now I'm not the sharpest tool in the shed and I don't pretend to be. I also agree Figure 5 doesn't seem right in that paper, but 6 and 7 do seem correct along with the rest of the document. Like I said I found it and it fit what I have had in class's on equipment safety. I also agree with JasG at times Spyderlk I can not follow what you are trying to explain at times. Which you may be the smartest guy on the planet, but if you come across in a way that 1) can't be understood, and 2) is to be so unwilling to explain why your point is correct you won't be of use to many people. You say you learned it and it's in your head. I work with engineer's everyday, all of them very smart and hardworking. Not one of them does everything from there head. They know where to find the correct formula, but unless it's one they use everyday they look it up. The electrical engineer's I have worked with carry "pocket" references just because of this. Not say you are wrong, but you are not in my mind explaining things very well and it at times conflicts with things I have learned over the years.

I am not unwilling to explain and the above posts go a ways toward it. In the interest of brevity [and laziness] they were written assuming a reader with a good grasp of the fundamentals. Even without that a question about my statement giving you trouble would help me address any issues in a directed manner. Instead were getting arguments that are based on links that the quoter has not fully understood. Sometimes a link will be correct but still mislead. Sometimes they are wrong in part or whole. Even worse there is the posturing, exaggeration, and twisting the flavor of my posts.
larry

 

[ampsucker]

so, to summarize:

"the angle of the dangle is proportionate to the heat of the beat when the throb of the knob is constant." (unless you have four wheel drive....)

yes, i have been called "thread killer".....

amp