Preventing tractor back flip

[LD1]

I think the whole problem here is trying to equate this with BOTH infinite power AND infinite traction.

XYZ: you say that the tires DO roll backwards if there is infinite traction. But you are forgetting the infinite power trying to drive the tires in the opposite direction as that. Therefore, if power AND traction are BOTH infinite, this equation cannot be solved. Because infinite power meas that the tires will NOT spin backwards. Meaning the ONLY way for the tractor to move backwars is to slip/spin. And THUS infinite traction says that THAT canNOT happen. So we are stuck with an unsolvable equation.

You diagrams ARE correct IF traction ONLY was unlimited.

If power ONLY was unlimited, wheel spin would be inevitable.

Somewhere between these two lies the "real" world. And the simple truth that hooking to the drawbar WILL allow the front to raise into the air, but only to a point. Because as the drawbar rotates downward and forward, either the load is going to move, or the tires will spin. Both resulting in the front wheels settling back down. In the "real" world, flip-over highly unlikely. And the cases where it happens is most likely a result of operator error(running start, popping clutch, jerking, etc) or terrain, like pullig up a steep hill.

 

[LD1]

Let's forget all the details we've been discussing and ask ourselves two questions:

1. Is it possible for the nose to rise up when pulling at all? At least to some equilibrium point? ANY equilibrium point?


2. Is it possible for the nose to rise up with momentum?

If your answer to both of those is yes, then you must believe it is possible to backflip a tractor by pulling a load. Sure, there are other conditions and factors that may prevent it happening, but it's POSSIBLE.

xtn

Yes to both.

That is why I said 99% of the time. That other 1% for operator error. Things that cause enough momentum to actually backflip. Like jerking, running start, clutch popping, etc. and even steep inclines. I never did say it was impossible, because there are exceptions to every rule. But the physics clearly shows that is is VERY UNLIKELY. And in a steady/easy pull situation on LEVEL ground, it is NEAR impossible if the drawbar is lower than the axle CL.

 

[Egon]

2. Backflips
● The second type of rollover is a backflip. In this scenario, there are two forces in action. These are REAR-AXLE TORQUE and DRAWBAR LEVERAGE.
● Rear-axle torque is the transfer of energy between the engine and rear wheels of a tractor. It occurs when the pinion gear in the Differential meshes with the crown wheel of the axle. Thus, the pinion which is driven by the engine applies a rotational force to the wheels via the crown wheel ( Figure 6). This may be described as the rear axle rotating with respect to the chassis.
Torque reactive force
Crownwheel drives tractor rear axle
Pinion is driven
by engine (torque)
Crownwheel is driven by pinion
Figure 6: The basic drive mechanism of a tractor
● If axle rotation is prevented as in the case where the tyres are stuck ( eg. in a bog, frozen to the ground or if the load is very heavy), the rotational force moves the tractor backwards around the rear axle, lifting the front wheels off the ground and a backflip can result. Since a tractor痴 centre of gravity is closer to the rear axle than the front axle, it may only have to rear to an angle of 70 degrees for the centre of gravity to pass outside the rear tipping axis. This is located between the contact patches of the rear wheels.
● A backflip can happen in as little as 3/4 of a second. At this speed, there is little chance that the driver will be able to take evasive action ( Figure 7). There are many circumstances where the reaction time may be even less than 3/4 of a second. This can occur when the Centre of Gravity is already approaching the rear tipping axis, for example, when the rear wheels of the tractor are stuck in a bog.
● Practices which involve rear axle torque reactive force acting to cause a backflip include:
1. Driving off in low gear but with high engine speed.
2. Attempting to drive the tractor forward when the wheels are unable to move forward.
3. Rapid engagement of the clutch of the tractor.
4. Rapid acceleration, particularly when driving uphill or pulling a

Then we are equally arrogant.
/QUOTE]

Nope, I'll defer to you.

I've sat in the tractor seat doing things that could cause it roll over backward!:thumbsup:

http://farmsafewa.org/media/1377/Tractor Rollovers.pdf

 

[xtn]

I think the whole problem here is trying to equate this with BOTH infinite power AND infinite traction.

XYZ: you say that the tires DO roll backwards if there is infinite traction. But you are forgetting the infinite power trying to drive the tires in the opposite direction as that. Therefore, if power AND traction are BOTH infinite, this equation cannot be solved. Because infinite power meas that the tires will NOT spin backwards. Meaning the ONLY way for the tractor to move backwars is to slip/spin. And THUS infinite traction says that THAT canNOT happen. So we are stuck with an unsolvable equation.

You diagrams ARE correct IF traction ONLY was unlimited.

If power ONLY was unlimited, wheel spin would be inevitable.

Somewhere between these two lies the "real" world. And the simple truth that hooking to the drawbar WILL allow the front to raise into the air, but only to a point. Because as the drawbar rotates downward and forward, either the load is going to move, or the tires will spin. Both resulting in the front wheels settling back down. In the "real" world, flip-over highly unlikely. And the cases where it happens is most likely a result of operator error(running start, popping clutch, jerking, etc) or terrain, like pullig up a steep hill.

There is one thing that is infinite already as per the original question... The far end of the chain is infinitely immovable.

There are three things that MIGHT be made infinite: Power, Traction, and Weight of Tractor's Nose. We can make any two infinite and still have a workable situation.

We could have infinite power and infinite weight on the nose. The result is no traction.

We can have infinite traction and infinite weight on the nose. The result is no power to do anything, ie. no movement at all. But hey it's a solvable result.

And we can have infinite traction and power. The result is the nose comes up. And without something to stop it, it will keep going up and over.

Hmmmmm. Let's look at things from a different direction. My diagrams don't need infinite traction or infinite power. Power only needs to be enough to raise the nose and overpower the increased effort required as the drawbar approaches the ground. Traction only needs to be enough to put that amount of power to the ground without significant slippage. Neither one has to be "infinite." They just have to be enough to flip the tractor. Hey, I admit the tractor is unlikely to flip under normal circumstances, but if you want to know how it could happen even without jerking, that's it in a nutshell.

Let's look at it from another way still: You say infinite power will not let the tires roll backwards. That just isn't true. Since the weight on the nose is not infinite, the infinite power can flip the tractor over backwards with the tires locked into position, right? Like if the tires are frozen to the ground, right? Rolling them backwards a foot or so while the power raises the nose isn't that much more to overcome than having them sit frozen to the ground while the power raises the nose. So your claim is false anyway.

I don't get why you are unable to reconcile an engine trying to turn the tires forward but them rolling backwards anyway. If there is enough (not infinite) power and traction, the geometry simply requires it and there is no way around that. Suppose you wrapped chains around the tires to hold them in place (simulating the frozen-to-the-ground scenario) the tractor could rear up and flip, right? Now suppose you use the chains to pull the tires backwards a bit while that is happening... would the universe explode? No of course not. The tires can roll backwards - if the net sum forces dictate it - at the same time the engine is twisting the tractor up and over, and this can all happen without breaking any laws of physics. And when the drawbar is chained to an immovable object, the net sum forces DO dictate it.

xtn

 

[eray1066]

Sorry forgot to post the video link
1960 vintage John Deere 830 tractor pull wheels up wheelie - YouTube

 

[xtn]

Egon,

1. In your post, #193 above, I have no idea what point you're trying to make with regard to the current discussion, and I'll be surprised if anybody else reading this has any idea. We are currently exploring the dynamics involved way beyond what the text in your link describes. I mean nothing is wrong with it, but it's an incomplete analysis compared to this thread, so I don't really know what your point is. Anybody know what the point of Egon's post is? Please chime in if you get something relevant from Egon's post that I've missed.

2. If I'm arrogant for thinking I might have had any effective input to a thread, aren't you equally arrogant for just deciding that I wouldn't have?

xtn

 

[Short Game]

Anyway, now this topic is going in circles...

Maybe even doing back flips involving immovable objects.

It's been okay though. Fun to watch. I was out in tractor land today and got way behind.

 

[Short Game]

...there are exceptions to every rule.

That looks very much like a rule. My head is hurting to think out that.

 

[SPYDERLK]

I think the whole problem here is trying to equate this with BOTH infinite power AND infinite traction.

XYZ: you say that the tires DO roll backwards if there is infinite traction. But you are forgetting the infinite power trying to drive the tires in the opposite direction as that. Therefore, if power AND traction are BOTH infinite, this equation cannot be solved. Because infinite power meas that the tires will NOT spin backwards. Meaning the ONLY way for the tractor to move backwars is to slip/spin. And THUS infinite traction says that THAT canNOT happen. So we are stuck with an unsolvable equation.

You diagrams ARE correct IF traction ONLY was unlimited.

If power ONLY was unlimited, wheel spin would be inevitable.

Somewhere between these two lies the "real" world. And the simple truth that hooking to the drawbar WILL allow the front to raise into the air, but only to a point. Because as the drawbar rotates downward and forward, either the load is going to move, or the tires will spin. Both resulting in the front wheels settling back down. In the "real" world, flip-over highly unlikely. And the cases where it happens is most likely a result of operator error(running start, popping clutch, jerking, etc) or terrain, like pullig up a steep hill.

The chassis rolls backward. We dont need infinite power .. just relatively high power and very low gearing so that extremely high force is available. Since things would progress slowly there would be no momentum issues. You posed tracks cast in concrete in a previous thread. To limit forces needed, use a 2 wheel tractor, long chain to limit angle change. : Short drawbar[< R]= full back flip, long drawbar[>R] = drawbar touches down and engine stalls or something breaks. Tractor moves backward in both cases after chain tenses.
larry

 

[LD1]

Let's look at it from another way still: You say infinite power will not let the tires roll backwards. That just isn't true. Since the weight on the nose is not infinite, the infinite power can flip the tractor over backwards with the tires locked into position, right? Like if the tires are frozen to the ground, right? Rolling them backwards a foot or so while the power raises the nose isn't that much more to overcome than having them sit frozen to the ground while the power raises the nose. So your claim is false anyway.

I don't get why you are unable to reconcile an engine trying to turn the tires forward but them rolling backwards anyway. If there is enough (not infinite) power and traction, the geometry simply requires it and there is no way around that. Suppose you wrapped chains around the tires to hold them in place (simulating the frozen-to-the-ground scenario) the tractor could rear up and flip, right? Now suppose you use the chains to pull the tires backwards a bit while that is happening... would the universe explode? No of course not. The tires can roll backwards - if the net sum forces dictate it - at the same time the engine is twisting the tractor up and over, and this can all happen without breaking any laws of physics. And when the drawbar is chained to an immovable object, the net sum forces DO dictate it.

xtn

CAll me hard headed, but I still dont see the tractor tires rolling backwards as the chain tenses up.

Stop and ask yourself what causes the front to climb up anyway? isnt it the the "equal and opposite" reaction force to the tires turning forward??

So if the tires roll backwards wouldnt the front set back down?

And dont we have the clutch engaged and infinite power trying to turn the tires forward?? yet, somehow that infinite power and traction tightens up the chain in a way the tractor rolls backwards??

And to open up another can of worms here, I think I an in agreement with Roy Jackson, in that a straightr pull, with the chain STRAIGH and LEVEL with the drawbar, if the drawbar is below the axle, it does pull down on the front.

XYZ: and others involved, I know it may sound childish, but I encourage you to do this. Get out one of your 1:16 scale model trators. Set this very expirement up. Attach a string to the drawbar and then to something immovable on a bit of an angle like your diagram. Then with your hands, try to drive the back tires. You can get a good bit of weight/traction just with your hands. You may be suprised at what happens. I did this yesterday before I even posted.