Hill Climbing Primer

[SPYDERLK]

SPYDERLK Did you miss the detail that the brakes were firmly applied? or the axle shaft welded to the housing?

In this exchange, the tires could be cast in concrete and there will be no different result.

The example is to demonstrate that forces seen within the tractor unit do not manifest external weight shifting unti "the rubber meets the road".

... or the axle meets the road so to speak. Axle welded to chassis allows no external interaction. Thats different than freezing the tire in place by external means..
larry

 

[SPYDERLK]

Did you know that the acceleration is different for the con rod as the crank passes over TDC than when it passes BDC? "thrown rods" nearly always happen at BDC .

A humorous aside. Do you know what the engineering unit for "rate of change of acceleration" is termed?

ready.....

It's a JERK! a detail we all seem to be quite well studied in from time to time ;-)

It should be the same if the engine is just being rotated and the wrist pin is centered in the piston. But running is not just being rotated. Forces vary per stroke. Also there is less relative velocity between bearing shell and crank throw at the bottom. That would be an issue to maintaining the hydrodynamic wedge that keeps parts from touching. Strange though that failure would show instantly from that. Im thinking that the culprit is the power stroke, perhaps many cycles later after damage occurs that causes the break showing at the bottom.

I try to change acceleration smoothly. :wink:

 

[ovrszd]

It can if theres no load and the wheels are frozen in place. The tractor wants to turn the axle but the axle wont so the tractor will go around if it.can. This is much different than a load causing tip. It is concievable that net tire rotation can be backward relatve to ground, ... Also different than a load point configuration that wont allow tip.
larry

Larry, you and I are finally on the same page. I think our differences have been because I don't know how to read the page you are sometimes on. But I can clearly read this page and we agree. As for CalG, he ain't quite there yet. Still wanting to weld axles or bury tires in concrete. Not sure how that even got in the discussion and it has absolutely no relevance to me.

 

[vtsnowedin]

There are a lot of people in this debate that I would not sell a life insurance policy to. :thumbsdown:

 

[CalG]

Well, It would be nice to see the ring climbing pinion die a sudden death without compensation ...

I'm still trying to advise the transmission housing that it need not worry about being lifted by anything other than turning wheels.

By the way, Has anyone ever seen a TRACTOR rocking in the parking lot or lifting a single front wheel when pulling out?

Must be those reactive forces are all resolved "internally".....

 

[Egon]

>>> Thats just it. It cant happen when the pullpoint is below tire contact. Both the propulsion lever and the pull [load] lever bear equal force ; one pushing forward, the other exactly offseting that push by pulling back. The pull lever is longer so the net torque is to tip the tractor forward. The ring gear is factored into the push lever. Theres no other effect in a steady state or statioanary pull. Acceleration or a hill would introduce COM effects.<<

>>All side tip forces would remain as if the tractor is off. Drive and driven torque are equal and opposite.<<

It does happen when the pull point is below the tire contact.
You need to convert all dem forces that are pushing on dem levers and get dem in the right places.
Wheels within wheels.

 

[SPYDERLK]

Larry, you and I are finally on the same page. I think our differences have been because I don't know how to read the page you are sometimes on. But I can clearly read this page and we agree. As for CalG, he ain't quite there yet. >Still wanting to weld axles or bury tires in concrete.< Not sure how that even got in the discussion and it has absolutely no relevance to me.

You are not equating these, right?

 

[SPYDERLK]

>>> Thats just it. It cant happen when the pullpoint is below tire contact. Both the propulsion lever and the pull [load] lever bear equal force ; one pushing forward, the other exactly offseting that push by pulling back. The pull lever is longer so the net torque is to tip the tractor forward. The ring gear is factored into the push lever. Theres no other effect in a steady state or statioanary pull. Acceleration or a hill would introduce COM effects.<<<

>>All side tip forces would remain as if the tractor is off. Drive and driven torque are equal and opposite.<<

It does happen when the pull point is below the tire contact.
You need to convert all dem forces that are pushing on dem levers and get dem in the right places.
Wheels within wheels.

Wrong.

 

[Egon]

Wrong.

Wrong!

 

[ovrszd]

You are not equating these, right?

Larry, nope, I definitely know the difference of those two. With the welds, the desire to elevate the front is gone. With the concrete, the desire to elevate the front remains, just as it does with zero tire slippage.

 

[CalG]

Perhaps we all can agree that the tension force on the load can NOT exceed the tractive force applied through the tire contact patch.

After all, it's the tractor pulling the load, not vice-verse. (no logs rolling off embankments have entered the scenarios.)

And so, the arm with the most leverage "WINS"!

 

[SPYDERLK]

Larry, nope, I definitely know the difference of those two. With the welds, the desire to elevate the front is gone. With the concrete, the desire to elevate the front remains, just as it does with zero tire slippage.

All of them are different in effect. The last is the traction situation.

Perhaps we all can agree that the tension force on the load can NOT exceed the tractive force applied through the tire contact patch.

After all, it's the tractor pulling the load, not vice-verse. (no logs rolling off embankments have entered the scenarios.)

And so, the arm with the most leverage "WINS"!

You got it, Put a metal plate on the ground. Attach two small crescent wrenches to it a few inches apart. Attach a big crescent between them. Stand on the little ones while pulling up on the big one. ... Thats how you pull yourself up by your bootstraps.

 

[Egon]

http://www.google.com/url?sa=t&rct=...fzBhJmRRU6s5EYh0g&sig2=-_GkrwXJW0H6G85j7Ph76A


pictures

 

[SPYDERLK]

http://www.google.com/url?sa=t&rct=...fzBhJmRRU6s5EYh0g&sig2=-_GkrwXJW0H6G85j7Ph76A


pictures

Note their own contradiction as to where tip occurs

 

[Egon]

Note their own contradiction as to where tip occurs

Note the simple diagram showing those "consolidated within forces"that take place when a flip occurs!

 

[SPYDERLK]

Too simple to tell the real story that the tip is around the ground contact if the tire is not attached to the ground.

 

[Egon]

Too simple to tell the real story that the tip is around the ground contact if the tire is not attached to the ground.

Really, a tire in float/fly mode?

The tractor rotates around the axle. Looks pretty obvious. It could be made much more complicated but doesn't change the outcome.

You gota a diagram?.

 

[msmith1wa]

I know it is not a tractor but the physics are the same.

Wheelies or wheelstands: From Physclips

 

[CalG]

I know it is not a tractor but the physics are the same.

Wheelies or wheelstands: From Physclips

Unfortunate that the physics of the example are not particularly related to hitch points or pulling a load.

Statics vs dynamics........

 

[CalG]

Egon's request for "diagrams" had me doodling on a bit of scrap paper.

IF one can get over that silly notion that the tractor front end is some how lifted by the pinion gear climbing the ring, a simple vector diagram allows the LOAD to pull on a stationary tractor with equivalent results to the opposite. In fact, the tractor engine need not even be running, and the transmission can be in neutral. The BRAKES must be set however (or the axle shafts welded to the housings ;-)

In such a diagram, The ONLY vector opposing the "pull" from the dynamic load is AT THE TIRE CONTACT with the ground, Opposite and equal to the horizontal component of the "load" vector, regardless of the height or direction of the load vector. Also, infinite tire traction is assumed (right up to the moment when the load lifts the rear wheels off the ground, should that condition exist.)

Something to consider