Pull from the front or the rear?

[California]

All sorts of possibilities
Funny videos indian tractor pulling HIGH 2 - YouTube

Ok. Mostly two tractors pulling back to back. At 1:14 the tractor went over backward - no ROPS - then the driver was crushed under the tire.

1:40 similar but an adequate ROPS. Hope he had a seatbelt because the tractor then rolled to the side. In that one the tractor balanced upright on its 3-point arms for a moment before going over.

 

[strantor]

All sorts of possibilities
Funny videos indian tractor pulling HIGH 2 - YouTube

Wow. I can guarantee none of those dudes did any vector analysis. Half of them are pulling from well above the axle. At least one of them is dead for sure.

 

[Kozzy49]

I agree with everyone else, if there is no option, pull from the drawbar.

Trying to pull from the front is not advised.

If you try pull from the front you risk damaging your loader if you try to pull off the loader body. Or damaging the bucket if load is
focused on the cutting edge.

Do not attempt to pull via the front axle, it was not designed to take this type of load.

In either case pull with extreme caution, high speed, jerk motions are a recipe for disaster. Better to get a tow truck,

 

[rScotty]

For me this has been an interesting discussion. I not only learned something about flipping tractors, it also helped with my understanding of intelligence, visualization, and education.

Trying to picture the changing forces as something rotates is really tough using nothing but words.
Not everyone is equally good at picturing things in their mind, although most of us think that we are.

I think a lot of the misconceptions have to do with the limited visualizations that are a part of a primarily written forum like TBN.
If we were all in a room together while talking and sketching out the loads and forces, I think we would arrive at the same conclusions rather quickly.
Thanks all,
rScotty

 

[the old grind]

.. The traction is perfect, (always, or assumed?) so it didn't come from slipping the wheels backwards. The chain presumably didn't stretch, either ... I haven't been to a tractor pull in a long time, but it seems to me that just about every tractor there either keeps the front wheels on the ground OR they float a foot off the ground. Floating signifies to me the actively balanced situation that is a compromise between solidly on the ground and the nose straight up. As the torque brings the wheels up...

Yes but ... I think in a real-world scenario the drive tires can hop and move backward. Then assuming nothing breaks, pouring torque into the ring gear will continue to 'climb the ring gear' and walk the tractor over backward if tire slip is insufficient. That torque has to go somewhere. Aside from tire slip, where else can it go? ...

Yes, vector analysis is very helpful to attempt to maximize your tractor's capabilities. Any of these assume constant pull, constant power, constant positioning, even constant weight. The problem is that none of the forces are constant. Wheels might grab on a rock, or the ground is more firm. The bounce of the front end might set off wheel hop. I used the term active balancing thumbsup:'Bikers do it!) on purpose to try to describe it. Unfortunately, there are forces that we can't necessarily see or predict that throw the balance off.

In theory, a pulling tractor should not be able to flip backward. ... There is still momentum to be considered - that's why I said virtually impossible. In addition most pulls limit front tires to rise no more than 24 inches above the ground. If they do the driver gets a red flag and their pull is over.

What??? Could that even happen if 'pulling' tractors are hitched per rules?

I ask if the tires are the point of pull and not the axle, why does our paper-only vector analysis only refer to the latter?
It's been mentioned before that tongue weight influences rotation about the axle.
Do our vector analyses ever account for that?
Regardless of where hitched in the Indian videos (obviously too high and causing front end lift) slipping tires DO keep a loser's front end up in the air. (Thanks, CalG!)
Once again,

...vector analysis is very helpful to attempt to maximize your tractor's capabilities. ... Any of these assume constant pull, constant power, constant positioning, even constant weight ... The problem is that none of the forces are constant... Unfortunately, there are forces that we can't necessarily see or predict that throw the balance off.

(Thanks, Ray!)

 

[MHarryE]

It is a simple vector analysis. Sum of the moments must be zero or the tractor will flip over. Pivot point is where the rear tires meet the ground. Opposing moments are tractor CG in front of that pivot point. Opposing that is pull at height above ground. Using English units assume CG is 2 feet in front of wheel contact point and tractor weighs 5000 pounds for 10,000 ft-lb moment. Assume drawbar is 2 feet above ground level. At 5000 pounds pull which is 1 to 1 coefficient of traction, possible with tractor tires, the front wheels lift off the ground. If the hitch point is 2 feet behind the tire contact point assume it drops to 1 foot as the tires lift. The CG will only move back by the cosine of the lift angle. Or now 9,000 foot pounds trying to hold it down vs 5,000 ft pounds trying to flip it over. When the drawbar hits the ground the flipping moment reaches zero. Centerline of the axle is not involved. When a free body diagram is drawn the outside forces acting on the body are the ones that are involved I.e the ground contact point and drawbar height, distance behind the ground contact point to the hitch point.

 

[MHarryE]

http://ecoursesonline.iasri.res.in/pluginfile.php/3034/mod_page/content/9/218.png

 

[CalG]

http://ecoursesonline.iasri.res.in/pluginfile.php/3034/mod_page/content/9/218.png

All I know, is I want that rigid draw bar to go to ground long before the front end gets past 45 degrees over the horizon.

 

[CalG]

It does not matter whether the point of attachment is above or below the axle. It matters how high it is above the ground. Lower is better. The drawbar pulls backwards and the bottom of the wheel pulls forward. This produces a torque on the tractor that could flip it over backward. Next you have to know where the center of gravity is of the tractor and the tractor's total weight. Then do the math or do the experiment. With a little luck the wheels will slip before the tractor flips backwards.

This is wrong!

 

[California]

It is a simple vector analysis. Sum of the moments must be zero or the tractor will flip over. Pivot point is where the rear tires meet the ground. Opposing moments are tractor CG in front of that pivot point. Opposing that is pull at height above ground. Using English units assume CG is 2 feet in front of wheel contact point and tractor weighs 5000 pounds for 10,000 ft-lb moment. Assume drawbar is 2 feet above ground level. At 5000 pounds pull which is 1 to 1 coefficient of traction, possible with tractor tires, the front wheels lift off the ground. If the hitch point is 2 feet behind the tire contact point assume it drops to 1 foot as the tires lift. The CG will only move back by the cosine of the lift angle. Or now 9,000 foot pounds trying to hold it down vs 5,000 ft pounds trying to flip it over. When the drawbar hits the ground the flipping moment reaches zero. Centerline of the axle is not involved. When a free body diagram is drawn the outside forces acting on the body are the ones that are involved I.e the ground contact point and drawbar height, distance behind the ground contact point to the hitch point.

Does that analysis include the torque that the pinion gear is exerting against the ring gear?