Hill Climbing Primer

[joshuabardwell]

The axle has to apply the torque.

I think what you're saying is that the tractor tips backwards, not because it's trying to "drive out from under" the attachment point, but because the axle must keep turning, and if the wheel can't go clockwise, the tractor is going to go counter-clockwise. Is that right?

 

[SPYDERLK]

That is the net effect. ... But in essence it is the two levers of different length described that are acted on by the same amount of force that favors a tip.

... I will have to continue this evening.
larry

 

[Gordon Gould]

Please read my prior post. #31, I believe. The site works so poorly that you cant multi quote - among other features that cant be relied on.

The pull point is not the attachment point of the arms on the tractor. Instead, when the ball ends are held above the attach point the effective pullpoint is at the height of the ball ends. Otherwise you are right. Take a look at the link post 35 with BabyGrands attach method and note the difference in how the forces resolve.
larry

I have thought and thought about what you were trying to tell me and have finally grasped your message. I knew the front end lightened when using the lift arms as a pulling point. I thought this was solely from the weight of the log. What I didn't comprehend was that some of this front end lightening that I feel is due to the horizontal pull acting on the angled lift arms thru the 3ph components as you said. Now that I see it and the mechanics of it are so basic and obvious I am embarrassed to have not realized this before and even more embarassed it took me so long to see it after you told me.

So I was wrong in stating the horizontal pull force is always at the lift arm connection point to the tractor below the axle. I agree that it moves upwards as the lift arm raises above horizontal.
Thank you for your patience. And I apologize for spouting misinformation on this great forum.

I can now see the merit of running a chain from the raised log to the draw bar to keep the pull force at a low point. What a great idea.

gg

 

[Egon]

Back Flips:

Enough torque, enough traction and the tractor will rotate around the rear axle. Don't mater how low you hitch.:thumbsup:

 

[Looking4new]

I am embarrassed to have not realized this before and even more embarrassed it took me so long to see it after you told me.
gg

Better to be embarrassed than dead. A lot of good people have ended up dead from tractor roll overs backwards.

 

[square1]

Enough torque, enough traction and the tractor will rotate around the rear axle. Don't mater how low you hitch.

Visualizing Dragsters / Funny Cars has helped me grasp the concept.

 

[Egon]

Visualizing Dragsters / Funny Cars has helped me grasp the concept.

Well know concept long before funny cars or dragsters!

 

[Raised on a Deere]

The trick we used back before 3 point hitches was to use an extra long draw bar. As the tractor front end would rise the drawbar went toward the ground. People with short draw bars saw the front end come higher off the ground in a hard pull. Pulling at ground level there is no tipping force except for whatever is generated when the rear wheel climbs out of a hole. Tractors had to be a lot bigger to drag logs with out being able to pull up high lifting the logs off the ground and adding weight to tires but tipping was not much to watch out for other than what you would regardless of load.
Just what was said about funny cars etc.

 

[ovrszd]

Back Flips:Enough torque, enough traction and the tractor will rotate around the rear axle. Don't mater how low you hitch.:thumbsup:

Yep. The rear axle pinion gear is trying to climb up the front of the rear axle ring gear. Same thing happens in any rear wheel driven vehicle when engine power is applied. That's why Dragsters use wheelie bars even though they have no load hitched to the rear of the car.

 

[SPYDERLK]

I have thought and thought about what you were trying to tell me and have finally grasped your message. I knew the front end lightened when using the lift arms as a pulling point. I thought this was solely from the weight of the log. What I didn't comprehend was that some of this front end lightening that I feel is due to the horizontal pull acting on the angled lift arms thru the 3ph components as you said. Now that I see it and the mechanics of it are so basic and obvious I am embarrassed to have not realized this before and even more embarassed it took me so long to see it after you told me.

So I was wrong in stating the horizontal pull force is always at the lift arm connection point to the tractor below the axle. I agree that it moves upwards as the lift arm raises above horizontal.
Thank you for your patience. And I apologize for spouting misinformation on this great forum.

I can now see the merit of running a chain from the raised log to the draw bar to keep the pull force at a low point. What a great idea.

gg

... No need. I really appreciate you persisting in analytic mode. These things only become obvious when all the almost correct diversions can be appropriately sorted. This perspective is not easy to see or to convey. I have a real hard time eliminating all the stinkin thinkin pitfalls as I try to turn the concepts every which way in my head.

Pardon me for addressing one of your statements that I think you are correct in, but leaves room for an interpretation that would be an "almost correct" diversion. >> The pullpoint is moved upward to the endballs when the arms are held up above the horizontal. If the tractor then backtips there will come a point when the arms are horizontal. At, and beyond that tip angle the pullpoint moves to the arm/tractor ball articulation attachment point [Which unfortunately for this issue has a location so near the axle that it stays at constant H during tip.].Effective pullpoint stays there after the arms become horizontal during tip and while they float to their max H. Here they encounter resistance forcing the endballs down below horizontal. THEN the pullpoint reverts to the ball ends.Tip is now becoming less favored, but it is already tipped a lot, perhaps beyond balance ... and even if not, the loaded components are not designed for loads that push on them and will probably fail as the ball ends near ground, and allow tipover.

As unlikely as it is to get a tractor into this situation, certain changes from what the operator is used to and has come to expect can increase traction or influence another factor so much that all previous "safe" use is moot. Fitting chains to industrials would likely be such a critical change. To deal with the significantly more aggressive pull in a manner favoring maximum performance with safety the physics of the tractor system must be applied in as wholly complimentary a fashion as possible. The designer has provided features that can let you do this conveniently. The configuration challenge is left to you.
.... Baby Grands configuration affords access to every advantage; =] You can lift as much of the load weight as you want or can with the hydraulics, =]You can tie the load to the fixed drawbar with a little slack, =] as you move forward the load hangs back and, if it wasnt clear of the ground to start, more lift force acrues increasing traction, =]you can tune the setup by varying the amt of lift, amt of slack in the forward tie, and height and length of the drawbar. ... You can tailor it as far as the point where you are supporting as much as the big end portion of the load and all the tractor on the rear wheels and be in a stable safe pull with the front wheels hovering at the ground. Any further backtip is automatically stabilized in 2 ways; 1]reduction of weight supported as you have said, and, 2] dipping of the drawbar end causing a lower pull point. Seems to me this might be the absolute limit to the pull available and as safe as you can make it.

Could be fun!
larry