Drawbar pulling question

[MHarryE]

From my engineering textbook, copyright 1952 but laws of physics haven’t changed. To maintain equilibrium, F, tractive force where tire meets ground times distance y1 must be less than weight at front tires W2 times distance x1. You tip backwards when W1 times y1 is greater than W2 times x1. Figure 14.8 shows what’s needed to calculate having drawbar pull not parallel to the ground, and also adding a slope. These free body diagrams should help illustrate things discussed here. Pulling from the 3 point raises or lowers distance y1. Usually there is enough weight at W2 to keep the system static but increase y1 too much and the front tires leave the ground.

 

[bcp]

If you have the tractor's original fixed (not three point) drawbar installed, pull from the rear of it, like the factory's engineers designed it. They knew what they were doing. No more drawings needed.

If not, get one or copy it.

https://www.southernfarmequipmentimports.com/collections/ym2310-3-point/products/sfdb-4420-drawbar-3-point

Bruce

 

[RancherGuy]

I have 3 choices from where to pull. I can use the point where the top link attaches, the arms of the 3 point hitch, or the drawbar. The top link is too high. The 3 PH arms can be positioned where ever I want and they are well behind the axle centerline. So if too high they would tend to torque the front end up. But even if set low to the ground will they tend to raise the front end? I need to think about this a little. Using my Ford 9N I nearly flipped it over pulling a big log. Using a drawbar in the 3 PH arms. Scared the crap out of me. I was truly surprised that the front end didn't break when it came crashing down. Lucky for me that the tractor torqued to the right and came down on a bunch of blackberry bushes which lessened the iimpact. Well, I now have to add 3 more points to the previous two mentioned. Using the drawbar, which is below the rear axle, the chain can be connected behind and below, on the centerline and below, or ahead and below. These options need to be compared to the 3PH arms option of much farther behind and a varying degree of below. Time to make some more drawings.
Eric

I'm sure you can appreciate potential problems with a 3 point hitch. They can lift, but they cannot stop something causing them to lift. As you pointed out, there is a benefit, especially if you adjust or pin them so they reach lower, whichever is available in your design. Again, if low enough, the front should not get light and may never lift. Top link with a strong pull is definitely out.

FWIW, I've experienced a 3,000 pound tractor nose pointing straight up, as well as lifted tires of a 16,000 pound tractor when I connected to the top link area. Nothing fun about it if you weren't planning on that response.

 

[etpm]

If you have the tractor's original fixed (not three point) drawbar installed, pull from the rear of it, like the factory's engineers designed it. They knew what they were doing. No more drawings needed.

If not, get one or copy it.

View attachment 723975

https://www.southernfarmequipmentimports.com/collections/ym2310-3-point/products/sfdb-4420-drawbar-3-point

Bruce

I have the original, similar to the drawing. After looking at posts here, especially the drawings from the engineering textbook, I am more inclined to turn the bar sround. I'm still gonna make the drawings to scale to figure out the forces on the bolts.
Eric

 

[ROUSTABOUT]

I'm no expert, but I've read elsewhere it is strongly advised not to do this.

You for sure don't pull backwards with a 4x4, of any type.

 

[ROUSTABOUT]

I'm sure you can appreciate potential problems with a 3 point hitch. They can lift, but they cannot stop something causing them to lift. As you pointed out, there is a benefit, especially if you adjust or pin them so they reach lower, whichever is available in your design. Again, if low enough, the front should not get light and may never lift. Top link with a strong pull is definitely out.

FWIW, I've experienced a 3,000 pound tractor nose pointing straight up, as well as lifted tires of a 16,000 pound tractor when I connected to the top link area. Nothing fun about it if you weren't planning on that response.

Saw my brother do that with a 15,000# tractor. Instantly.

 

[etpm]

If you have the tractor's original fixed (not three point) drawbar installed, pull from the rear of it, like the factory's engineers designed it. They knew what they were doing. No more drawings needed.

If not, get one or copy it.

View attachment 723975

https://www.southernfarmequipmentimports.com/collections/ym2310-3-point/products/sfdb-4420-drawbar-3-point

Bruce

I have the original, similar to the drawing. After looking at posts here, especially the drawings from the engineering textbook, I am more inclined to turn the bar sround. I'm still gonna make the drawings to scale to figure out the forces on the bolts.
Eric

 

[jonsstihl]

do not turn the bar around. Y1 is still not zero technically you could still flip the tractor if you could get enough traction even with the drawbar backwards. as the wheels lift your attachment point will raise instead of lower than the theoretical Y1 will become the rear axle where the chain is bending . A fixed drawbar extending behind the rear wheels is the safest bet.

 

[5030]

Keep your attachment point (whatever it is) BELOW the rear axle. Excessive pulling force applied will then tend to pull your front end down not up.

EXACTLY....

 

[Egon]

Whether pulling or pushing on the drawbar the bolts holding it to the tractor will see the same load. The drawbar on my tractor is so large in diameter that my tractor cannot develop enough force to bend it. It is surprisingly, to me, beefy.
Eric

The forces generated wil be much different.

 

[arrow]

One of these may help in regards to logs digging in:portable-winch-pca-1290-skidding-cone.
From end weights will go a long way to keep the nose down.
If you ever get to a tractor pull, notice those tractors have "wheels bars" attached to the backs of the axle to prevent that which you are worried about.:

 

[Egon]

I’d hate to trust those bars to prevent a backflip!

 

[jonsstihl]

they might just sink in the mud and you would still go over

 

[oosik]

The simple answer. Leave the drawbar in its OEM position. Run a chain from the drawbar to the log. If this does not work - get a log arch. If this does not work - get a larger tractor. Most anything else will cause damage, injury or a back flip.

 

[Cougsfan]

You for sure don't pull backwards with a 4x4, of any type.

Why? I am always amazed when I find I have done things wrong my whole life without ever having a problem.

 

[etpm]

Why? I am always amazed when I find I have done things wrong my whole life without ever having a problem.

I don't know if this is true and it should apply to both 4 and two wheel drive but I was told that the pinion gear could break. It was explained to me that the way the differentials are generally made results in the pinion gear being subjected to less stress when driving the vehicle forward. This makes a little sense to me after setting up the front diff in my jeep years ago, getting the tooth contact pattern right. Anyway, having the diff apart it was easy to see that the pinion gear was stronger driving in one direction than the other. This was because of the shape of the teeth and how they contacted the ring gear. But I don't know how much weaker the pinion is when driving in reverse.
Eric

 

[oosik]

Yea-hootie-christ. Another wives tale. I've never hesitated to pull in reverse with either of my tractors. The first one - 27 years and no damage. Now the 2009 Kubota M6040 - no damage.

Both were/are 4WD. Like Cougsfan - all my life and doing it wrong. Give it a break.

Librium will help your fears Roustabout.

 

[arrow]

they might just sink in the mud and you would still go over

Depends on his terrain. Bottom plates could always be made larger for softer ground.
Ya think he'd rather have nothing as opposed to these?

 

[arrow]

I’d hate to trust those bars to prevent a backflip!

Exactly what they're made for.
I guess one would have to see them in action to be secure with their workings.

 

[RoyJackson]

Watch tractor pulls illustrates having the attachment point below the axle does not keep the front from coming up. As someone else stated, the pivot point is the tire to ground contact point. Pulling tractors have often have their front end raise, and because the drawbar attaching point is well behind the ground contact point, when the front end raises, the drawbar attaching point lowers until reaching an equilibrium. Sum of the moments must equal zero. If tires get a super bite, there is a very large moment trying to raise the front. As seen in many videos, releasing the clutch immediately reverses the moment diagram and the front end comes down with full weight of the engine(s) in front of the ground contact point providing the wallop breaking tires off, axles off, and even splitting tractors. Operators illustrating the same phenomena are those chaining trees to the rear axle. In those cases torque might be enough to flip the tractor.

I'd be very surprised if most tractors have the HP or torque to do what a dedicated tractor for pulls can do