Dynamic Rear Weight

[npalen]

A question comes to mind after reading some very interesting threads on adding weight to the 3PH. Would it make sense to build the weight system so that the attachment point of the toplink would cause the weight to tip back when the 3PH is raised? I would envision a fairly tall weight configuration such as, for speaking purposes, a 30 gallon barrel full of whatever. An unusually long top link would cause the tipping action with the advantage being that the weight could be lowered and tilted forward when it is not needed. This would transfer some weight back to the front of the tractor.

 

[swick1]

That would work great if you only drive on a concrete pad. The further it hangs out there the more likely it is to hit something. Members with backhoes will agree. Just buy a hoe

 

[npalen]

I was thinking that the only time the weight would be "extended" is when it's needed to counterbalance an unusually heavy load in the FEL bucket. The rest of the time it could be left in the "retracted" position for clearance. A hydraulic top link would provide or add to the same effect.

 

[swick1]

Yeah but it would need to swing from side to side if it sticks out that far and you drive on uneven terrain which is why I said a backhoe is a great counterweight.

 

[npalen]

Yes, I agree that a backhoe is a great counterweight but not everyone has one. I guess a TnT would accomplish the swinging side to side that you mention unless I'm misunderstanding.

 

[Gary Fowler]

I cant see you getting much dynamic force from anything that you could put back there. You are limited by the lifting force of your 3 PH. Then you are limited in the backward offset by the amount of clearance from the ground. You have to be able to pick it up by some amount so it doesnt drag the ground and most 3 PH arms only move 18-24". Allow 4" ground clearance and that only allow 20" of offset behind the pins x 1000 or so in weight and some of that weight will be above the pin and will therefore transmit it weight forward but still behind the wheels so assume 80/20 split so about 800# of dynamic force moving 14-20" behind the pins.
Any of you engineers want to calculate the additional force that this would apply to the rear wheels? Dont forget to subtract the 20% that is moving in front of the pins so that leverage is then lessened

 

[swick1]

Just find out where the center of mass is in all positions and multiply the horizontal distance between it and the axle center to find the torque exerted on the tractor regardless of how the counterweight is shaped.

 

[swick1]

Yes, I agree that a backhoe is a great counterweight but not everyone has one. I guess a TnT would accomplish the swinging side to side that you mention unless I'm misunderstanding.

Yes I agree with both points. If you have tnt though I think the tractor should be big enough to handle a large static counterweight. For my tractor in tight spots I was actually going to go the other way with a much heavier counterweight tucked in between the arms rather than slamming my hoe into everything.

 

[LD1]

I have to agree with the other posters that it just inst going to create enough of a change to matter.

The limiting factor is that the lower links are a fixed length and can only raise a given height. And the 3PH raises in an arc. So the higher it raises (normally) the closer the implement comes to the tactor. With a top-heavy weight and a long toplink like you are suggesting, I dont think it will gain anything on the raise. Maybe just enough to offset the the arc travel of the 3PH. Just make the counterweight heavy enough to start with

 

[SSdoxie]

I have to agree with the other posters that it just inst going to create enough of a change to matter.

The limiting factor is that the lower links are a fixed length and can only raise a given height. And the 3PH raises in an arc. So the higher it raises (normally) the closer the implement comes to the tactor. With a top-heavy weight and a long toplink like you are suggesting, I dont think it will gain anything on the raise. Maybe just enough to offset the the arc travel of the 3PH. Just make the counterweight heavy enough to start with

I too agree. Plus I think having a top heavy weight like this may add to risk of roll over on a side slope versus working to hold both rear wheels down.

 

[npalen]

Great feedback guys! Much appreciated.

 

[schmism]

with a hydraulic toplink you could do it (purple bar).

something like this.

remember stroke lenght of the top link to rotation of the counter weight is relative to the distance between the 3pt pins and were you attach the top link on the green "bar" BELOW the pivot point.

It would seem that some follow up math to show how much weight you could "gain" by doing that is in order also as many people dont think it accounts to much (but it does)

 

[xtn]

It's doable without a top link at all.

The weight would be designed to mount where the top link mounts to the tractor, and to pivot up and down around that mount just as a top link would. Most of the mass would be concentrated at the other end. Along the lower side of the weight would be a slot running fore/aft. Through this slot would be a bar attached to the lower lift arms. If you get the geometry right, lifting the 3pt would tilt the weight up and rearward.

 

[schmism]

It's doable without a top link at all.

The weight would be designed to mount where the top link mounts to the tractor, and to pivot up and down around that mount just as a top link would.

THat was my inital thought also, simular to a PHD... but the problem you run into is insufficient height in the lower position, and if you rigged it were you had enough height, you wouldn't gain that much rearward travel as you brought the 3pt arms up.

But at some point you have to wonder about the complexity involved to achieve what stacking a few more chin weights on the rear of a standard ballest box does.

 

[JoeL4330]

with a hydraulic toplink you could do it (purple bar).

something like this.

remember stroke lenght of the top link to rotation of the counter weight is relative to the distance between the 3pt pins and were you attach the top link on the green "bar" BELOW the pivot point.

It would seem that some follow up math to show how much weight you could "gain" by doing that is in order also as many people dont think it accounts to much (but it does)

As the diagram shows, this would be a good way to raise your center of gravity ...and compromise your lateral stability ...but, why?

And, the only time I can think of when I suddenly needed more weight further back was when I was finish-mowing down a steep slope in 2WD (a no-no, don't try this at home) and when the rear wheels "unweighted" I had no engine braking and no brakes ...so, my "dynamic" solution was to raise (raise) the mower...it had been running on its wheels, contributing nada to rear weight; when raised, it "dynamically" put enough weight on the rears so I could stop gracefully ...and put 'er in 4WD.

If I actually wanted to design something to accomplish this, I would mount a boom pole on 3ph with max weight at end and a (castored) tail-wheel. Normal running, let it float and run on tail-wheel ...to super-weight the rear, raise the 3ph just enough to come off the tail wheel (and/or, hydraulically retract the tail wheel)...as long as the weight didn't raise above my over-all CG, I wouldn't be subject to an undesirable change in CG, which is what the diagram depicts ...or, perhaps I don't understand the issue.

Of course, this approach seriously compromises your turning radius. It may occur to you that this design solution will work in opposite fashion if the 3ph has no upward float (i.e., has down pressure) or if the boom-weight is attached to a sub-frame, and we've just invented a long "wheelie-bar"

 

[npalen]

http://www.laforge.fr/photosnews/challenger-sur-tracteur.jpg
Looks like this arrangement would sure provide some "weight leveraging".

http://www.laforge.fr/photosnews/challenger-sur-support-grand.jpg
This is the mounting arrangement for the weight most of which doesn't show up in the first photo above.

LAFORGE - News and innovations
Laforge has some cool looking stuff if you scroll down the page.

LAFORGE - Fleximass
Some more dynamic weighting system.