How much power, force ......

[loves80z]

I purchased a 1970 john deere 2520 from my mother in law. I've been lurking here ever since. I have build capability with steel and tools avaliable. I am an engineer by trade. Been designing factory automation for 20 years. I am a numbers guy. I do not accept "looks right" very well. I keep asking myself " how do i know my forces involved when 9 build an implement for my tractor" I found a document i wanted to share that gives me a starting point. 404 - File or directory not found., Draft, and Traction.pdf

 

[quicksandfarmer]

Find the maximum torque rating for your engine. Multiply that by the drive ratio in your lowest gear, that's the maximum torque the drive wheels can exert. Multiply by the radius of the drive wheels and you get the maximum drive force the wheels can exert. It's probably significantly overstated but it's a starting point for calculations.

 

[CNC Dan]

Find the maximum torque rating for your engine. Multiply that by the drive ratio in your lowest gear, that's the maximum torque the drive wheels can exert.

Multiply by the radius of the drive wheels

and you get the maximum drive force the wheels can exert. It's probably significantly overstated but it's a starting point for calculations.

Hmmmm. So bigger wheels = more drive force? I think you need to divide, not multiply.

Prehaps you were thinking of speed, not torque.

 

[firemanmike69]

6650lbs max drawbar pull

 

[BHD]

Drawbar (tested): 54.45 hp [40.6 kW]
PTO (tested): 61.29 hp [45.7 kW]

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1422&context=tractormuseumlit

TractorData.com John Deere 2520 tractor tests information

 

[quicksandfarmer]

Hmmmm. So bigger wheels = more drive force? I think you need to divide, not multiply.

Prehaps you were thinking of speed, not torque.

Yes, divide, my mistake.

 

[loves80z]

http://open-furrow.soil.ncsu.edu/Documents/DHC/Soil, Draft, and Traction.pdf
Tried again

 

[jb92563]

As a Civil Engineer I did plenty of force calculation scenarios in my career so I can help.

You need to account for all the worst case scenarios you might encounter and then design for those and add safety factors.
Then its a calculator festival to calculate all the forces and strength of materials to finally arrive at some concrete numbers.

What implement do you want to start with?
We can go through it together here for all to learn.

I'm no tractor expert but many others here can surely think of worse case scenarios that we did not think of.

Just some things to consider, for safety reasons you don't necessarily want your implement to be the strongest possible thing on your tractor.

For example, do you want your loader bucket to be so strongly (heavily) built so you could take out a bank safe, but it will be so heavy your rear wheels
will come off the ground and spin uselessly. Do you add more rear weight to correct for that, and then find your front axles failing under load.
Make one thing stronger and something else will break, you have to choose what you want failing first to save the more expensive parts.
Its all compromises so you have to design accordingly.

Now for those that are not engineering types, the "looks about right" trial and error based on experience, is a legit method as well.
That's why you need to be a good welder, if its too weak you can always add some reinforcement.
You just have to be extra cautious and expect your home made stuff to fail until you have proven its up to the task.

 

[loves80z]

HP and ground speed are the factors. Eliminate gearing and tire size in one shot and skip to ground speed. Some tractors only list pto hp. This paper estimates hp at the dirve as a factor of the pto HP. Also consider soil conditions. Then factor requirements based on per foot of implement width.

 

[loves80z]

jb
For simplicity sake I was thinking a box blade. First would be the rippers and cross members. One reason I default to engineering is because that is what I do every day. The other is because I have no practical tractor or farm experience. And yes.....being able to weld ad a back door is always helpful.

 

[loves80z]

BHD
The estimate of the pdf I found was 87% of pto hp for drawbar hp. That matches well enough with the numbers u posted.....on concrete. On firm soil it is 72% or 44hp.

 

[loves80z]

To generalize i size a shear pin for a little over BHD's drawbar force or 87% pto hp, size the width of implement based on the 72% of pto hp for firm soil i think i should be good. Anyone thoughts?

 

[RedNeckRacin]

Why not do some research on the dimensions of manufactured implements Instead of reinventing the wheel. I dunno what you other engineers LearNed I school but I learned to K.I.S.S. problems.

 

[SPYDERLK]

The max steady force you can apply is very near the weight the tires carry, if AGs. Getting brought up short will spike it higher.

 

[loves80z]

Thank you for the reverse engineer question. My thoughts: What size implement for my tractor? Do i need the heavy duty or the standard? My soil. What i have seen when i look at this is people listing what worked for them in their situation. I hope to define my situation then use that for a basis for all sizing. Sizing purchased, built, custom and revers engineering. I am much more cumfortable pointing to a chart and using it and some basic facts to make my selection as opposed to taking a pole and trying to figure out if i fit a situation and rely on an individuals opinion of what worked well for him. That being said the reason i am posting is that i value the opinion of the members here. I know that the situation is organ8c and cannot be completely defined with calculations without a lifelong effort and i want some impliments by spring. I need a baseline to start with. The pdf makes sense to me and will allow me to do some custome implements without the luxury of reverse engineering. That and the experience of people here to help me make sure i have not missed some factor i did not anticipate in my inexperience.

 

[jb92563]

I agree with KISS and also like that Nomogram in the PDF so perhaps the simple answer lays there.

Once worst case I can think of is when the box blade gets hung up on a root, rock etc you have the pull of the tractor to consider and you will want to know the fully ballasted weight, not just the factory spec, and of course your speed when the blade gets hung up.

We want to consider the strength of the drawbar or 3 pt elements so as not to break or bend the arms off. A shear pin is a good idea to protect your tractors parts.

 

[RedNeckRacin]

While I like to geek out on calculations I think you are over thinking things. Many manufacturer's will rate their implements based on pto hp or weight of the machine. AS long as your generally within their specs you will be more than fine. There is a general rule of thumb for rotary mowers and plows. I cannot possibly think of anything that you are going to gain by going through this exercise. Designing something for a tractor to be the most "efficient" is not needed. There are entirely to many variables to take into consideration. That's precisely where the "rule of thumb" rules came from. There is also a bias between the older iron from the 70'sa nd 80's vs the lightweight stuff from the current suppliers.


The other thing is, if your trying to save pennies, look around for used implements. Your likely going to find a great deal on something that is slightly larger or smaller than your tractor would be optimized with. This is not a problem. Rather a challenge to learn to operate your tractor within those limitations. After all, we all enjoy tractor seat time!

 

[BHD]

the Nebraska tractor tests have been considered the Bible on tractor horse power, as they have done independent tests for nearly as long tractors have been made,

most implements will have a recomedated tractor HP, for example I have a 10 foot mower and a 90 hp rated tractor, 96% of the time I have horse power to spare, but there are times when I am in weeds and grass that is as tall as the rear tires, you have to gear down,

same as with a chisel, normally I pull a 16 foot JD 100 chisel in the field, but I made a 7 foot unit for breaking up ground so I can break up soil to make the speed mover, (a towed box blade) work better in dry and unbroken ground, in un worked ground the 7 foot unit can make the tractor grunt,

much is how you going to use the implement, for example the speed mover, mine is a 8 foot unit, if one is just working the drive way, a 30 hp tractor could do it, but there have been times I have spreading truck loads of soil or a old farmstead that was dug up and removed from existence, and all the foundations and building removed the concrete buried about 10 feet below the surface, was at times all most more than my tractor could handle, (back it up on a mound that was as tall as the tractor cab and pull off a full box load of soil and spread until flat as a pool table,)

 

[BHD]

one more thing if your pulling hard you want some tire slip, up to 10%,

type of tires can make a big difference, a radial tire vs a bias ply tire, the Ag rear: 13.6-38 that were factory should be a good choice, yes a wider or a radial tire will provide more traction, but it would be better for the tractor to have some slip.

 

[loves80z]

One thing that has been very confusing to me is the hp ratings from manufacturers. A rotary implement using pto and shear pin is easy. Now i look at a box blade and its far from clear. A 55 hp land pride says i can use a 5 ft to 8 ft. I've read lots of threads about sizing and still walk away scratching my head. If i can use the charts like in the pdf i posted, the answer is clear. It factors in many variables and quantifies them pretty well. It tells me what information is needed and gives me a procedure.

I have never been accused of overthinking before.......well at least not in a few weeks.