Hill Climbing Primer

[ovrszd]

I've explained it more than once. I've also sat on tractors hitched low with the front wheels off the ground.

Yes you have. I've tried also. Seems we neither have used an example that is familiar to all. I still think if I could find a third member I might be able to display it in a manner that would be acceptable.

The pulling contest JD was a classic example but I'm afraid it was not accepted. I think we all need visuals. Your request for a force diagram was good but that seems to be unacceptable as well.

Oh well. It's all good.

 

[SPYDERLK]

I assume you are just trying to be funny.


But then,,,, if you don't know why the front tries to lift under power, you probably also do not know why the machine in fact does try to tip over sideways. This action is not visible on a vehicle without suspension but it is very noticeable in all others. Especially those with high torque engines such as big bore gassers or diesels. Go sit in a truckstop for 5 minutes watching the Semis come and go. You'll see both actions live and in person.


In an attempt to use examples that you might be familiar with, I also reference Super Stock cars at the drapstrip. Explain to me why they lift the left front tire first, then lighten the entire frontend and shift all that weight into traction to the rear tires???

A rigid body machine does not try to tip sideways. The trans output tries to rotate the body one direction, and the rear the other. The torques cancel. In the suspension case there is some windup before they cancel.
larry

 

[Egon]

(Originally Posted by msmith1wa
I am going to propose something that is not practical but takes what SPYDERLK is saying a little further.

Lets say there is an object that is to heavy or is theoretically immovable. Now lets dig a trench out from this object. Now fabricate a hitch that has the pull point below ground level. Now back the tractor up to the immovable object so that the trench is between the tires so that the hitch can be installed without dragging. Now pull on the immovable object with the tractor.

Will the tractor lift the front tires and tip over backwards? No it will not, in fact it will do just the opposite and actually force the front tires into the ground.)

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If the tractor is stationary and the engine is turning over the front comes up. Sufficient traction, sufficient torque and sufficient load and the front comes up. Oh, the point of rotation is not the tire ground contact but rather around the axle. The tire is stationary as there is sufficient traction so no rotation there. The pinion force excerted on the ring gear has to be greater than the force of the load and it's lever arm. Sufficient torque.

It's like putting a big fellow on a short wrench with a very small Fellar on the long wrench!

A simple diagram would show how the forces are applied. All dem consolidated.forces within the tractor they figure right in with the outside force's.

Depending on the direction of engine rotation on back tire will have a little more down force on it.
.

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[ovrszd]

A rigid body machine does not try to tip sideways. The trans output tries to rotate the body one direction, and the rear the other. The torques cancel. In the suspension case there is some windup before they cancel.
larry

I had to think about that for a moment...... I agree. That's why once it's moving the Semi settles back into it's normal position.

Why does the rear axle try to rotate sideways??

 

[SPYDERLK]

I've explained it more than once. I've also sat on tractors hitched low with the front wheels off the ground.

How low?

 

[SPYDERLK]

Torque on driveshaft wants to twirl it like a propeller.

 

[Egon]

How low?

Lower than high.

 

[ovrszd]

Torque on driveshaft wants to twirl it like a propeller.

Yep, or to put it into context in this conversation, the ring gear tries to walk the circle around the pinion gear, or "climb" it. Actually,,,,, after some thought,,,, crawl under it.

Kinda the same reaction that takes place when the pinion gear tries to walk the circle around the ring gear???

In regards to the axle housing it causes the axle housing to rotate sideways. In regards to the third member assembly it causes the axle housing to rotate backwards, which in turn causes the front of the vehicle to rise.

Pretty simple huh. Minus lengthy mathematical explanations.

 

[CalG]

Egon and my points are simply that there is no need for calculus or dynamics or statics or vectors or triangles or any other such methods of description. It's very simple. I was just curious if you could explain it. But now I'm not sure.

I scrounged thru my boneyard but couldn't find an intact third member. I'll check at my Son's shops and if I find one I can explain it all with 30 seconds of video, no charts, graphs, vectors or formulas. Just simple logic.

Wait,.... Egon is the one asking for vector diagrams....

I did dig through some of my scrap.
Two open differentials, one from a garden tractor complete with three speed transmission. and the other from a golf cart. Unfortunately, neither is "ring and pinion". and neither has a removable cover or a pumpkin to pull out.

If there is confusion regarding why engines rock, the front tire lifts or the rear squats, or why there is a traction bias (weight transfer) to one rear corner of an accelerating vehicle fitted with a "typical" solid axle rear end, I'm afraid there is a gulf between us.

How would you ever describe the resolution of forces on an excavatore?, or even a bridge? Does F=ma do anything for you? For me, the equation highlights the gravity constant, turning "mass" into weight ;-)

Don't let this come off as "personal", the conversation is stimulating.

 

[SPYDERLK]

(Originally Posted by msmith1wa
I am going to propose something that is not practical but takes what SPYDERLK is saying a little further.

Lets say there is an object that is to heavy or is theoretically immovable. Now lets dig a trench out from this object. Now fabricate a hitch that has the pull point below ground level. Now back the tractor up to the immovable object so that the trench is between the tires so that the hitch can be installed without dragging. Now pull on the immovable object with the tractor.

Will the tractor lift the front tires and tip over backwards? No it will not, in fact it will do just the opposite and actually force the front tires into the ground.)

---

If the tractor is stationary and the engine is turning over the front comes up. Sufficient traction, sufficient torque and sufficient load and the front comes up. Oh, the point of rotation is not the tire ground contact but rather around the axle. The tire is stationary as there is sufficient traction so no rotation there. >>>The pinion force excerted on the ring gear has to be greater than the force of the load and it's lever arm. <<< Sufficient torque.

It's like putting a big fellow on a short wrench with a very small Fellar on the long wrench!

A simple diagram would show how the forces are applied. All dem consolidated.forces within the tractor they figure right in with the outside force's.

>>Depending on the direction of engine rotation on back tire will have a little more down force on it.<<
.

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>>> 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.<<