Center of Gravity Calculations and static tipping angles. Am I doing this right?

[MossRoad]

Possibly. I would have though with it kept low, it would lower the CoG, regardless of where it is suspended from. The FEL is suspended at a point higher than the CoG of the tractor, yet with it low to the ground, ot lowered it. And the higher the FEL is elevated, the higher the CoG

Just because its low to the ground doesn't mean its weight is supported low to the ground. The brush hog is supported behind the rear axle, further from the center of gravity. The FEL is supported between the axles, close to the center of gravity.

Try this (without the neighbors watching).
Stand on your right foot with a full oil can in your left hand and extend your left arm all the way out to your left side, keeping your right arm at your side. You can feel your body pulling to the left. Now bring that oil can in and hold it against your stomach. You stable right up, don't you? The oil can out to the side represents your brush hog. The oil can at your belly represents the FEL. No weight ever changed. Just the location of the weight.

 

[LD1]

CalG: the purpose of doing the front and rear is to locate the cog height. I am not lifting one rear tire. I am lifting BOTH of them.

That is standard procedure for locating cog height. Raise one axle a given distance and measure the amount of weight added to the other. And then with some calculations, you get the height.

The lower the cog, the less weight transfered. The higher, the more weight.

So in a way, it isn't finding the side tipping angle, but rather just a part of it.

 

[LD1]

CalG: the purpose of doing the front and rear is to locate the cog height. I am not lifting one rear tire. I am lifting BOTH of them.

That is standard procedure for locating cog height. Raise one axle a given distance and measure the amount of weight added to the other. And then with some calculations, you get the height.

The lower the cog, the less weight transfered. The higher, the more weight.

So in a way, it isn't finding the side tipping angle, but rather just a part of it.

 

[LD1]

Flusher: this is mostly just for fun and education. I have already done a small mod to be more stable. 1.5" wheel spacers.

I mowed some 22 degree slopes about a month ago. Right on the edge of my pucker factor. I have no intent to do anything steeper. But was just curious as to how close I was to actually being in danger of an upset.

I know 22* seems really steep when on the tractor. But standing back behind the machine 20' and holding a straight edge at 22*, doest look even remotely close to being upset territory.

 

[MossRoad]

Something else you should be aware of is how many degrees of tilt is your engine's lubrication system rated for. Too long at too steep an angle can starve the engine of oil. Mine's rated at 25 degrees. Some other models from the same manufacturer are 20, some are 45. Worth looking into if you plan on mowing slopes often.

 

[mikehaugen]

Your center of gravity is higher with the brush hog on because the brush hog is not on the ground. It is suspended from the tractor at a point higher than the "normal" center of gravity as measured when the brush hog is off. Make sense?

Sorry Moss, but I have to disagree with this statement... if I understand what you are trying to say. I think you are saying that it doesn't matter what height the bh is, because it is suspended higher, so it would be putting the weight higher. Since the bh is more or less "fixed" in position (left to right and front to back) the weight is dependent on the position of the bh, not where it is attached. For an example, imagine a 3 foot high pole, now imagine a bar with a 90 degree bend at the top, welded to the to top of the pole where the bottom of the bar and the bottom of the pole are at the same height. Now place a weight on the bottom of the bar. If you tip the pole left or right, the weight stays at the same position as the pivot point of the pole and has no leverage on the pole whatsoever, even though it is attached to the top of the pole. The tipping force on the pole is the same with or without the weight there. Now if the bar gets shorter (the weight moves up) then it starts to have an effect. The only difference is the position of the weight to the pivot point of the pole, regardless of where it is attached to the pole.

Now if the weight were free hanging, say from a chain or something, then things get different.

 

[mikehaugen]

Something else you should be aware of is how many degrees of tilt is your engine's lubrication system rated for. Too long at too steep an angle can starve the engine of oil. Mine's rated at 25 degrees. Some other models from the same manufacturer are 20, some are 45. Worth looking into if you plan on mowing slopes often.

This is a good point, I'm not sure how readily available this information is though. I don't ever recall seeing it my operators manual. I remember looking for a new engine for my horse rototiller... it gets to a pretty steep angle once digging all of the way in and I was trying to find out if various engines could handle the angle. I checked 4 or 5 different manufacturers and IIRC Kohler was the only one that published a maximum working angle, and this is a splash lubed engine where I would think it would be even less tolerant of extreme angles. I ended up taking my chances with a briggs and hoped for the best. I wish all manufacturers published this, but you may end up having to call someone to find out. Maybe Kubota is different?

 

[MossRoad]

Sorry Moss, but I have to disagree with this statement... if I understand what you are trying to say. I think you are saying that it doesn't matter what height the bh is, because it is suspended higher, so it would be putting the weight higher. Since the bh is more or less "fixed" in position (left to right and front to back) the weight is dependent on the position of the bh, not where it is attached. For an example, imagine a 3 foot high pole, now imagine a bar with a 90 degree bend at the top, welded to the to top of the pole where the bottom of the bar and the bottom of the pole are at the same height. Now place a weight on the bottom of the bar. If you tip the pole left or right, the weight stays at the same position as the pivot point of the pole and has no leverage on the pole whatsoever, even though it is attached to the top of the pole. The tipping force on the pole is the same with or without the weight there. Now if the bar gets shorter (the weight moves up) then it starts to have an effect. The only difference is the position of the weight to the pivot point of the pole, regardless of where it is attached to the pole.

Now if the weight were free hanging, say from a chain or something, then things get different.

I think I was referring to if the brush hog was on the tractor or off the tractor, not if it was raised or lowered. Anyhow, its an interesting fact finding mission. :laughing: