Loader boom pole

[Dave_eng]

If you raise the 600 lbs using a winch attached to the tractor or loader frame, the tension on the winch side is between the winch and the pulley, not between the pulley and the ground, hence only 600 lbs is seen by the FEL.

The discussion started when I cautioned that the pole needed to be much strong than the owner envisioned not that the load on the FEL was greater than the load being lifted. The boom pole was experiencing twice the crushing load the owner thought and could be at risk of buckling.

It has been a long time since I was in first year mechanics class but to understand the forces on the end of the boom pole imposed by the pulley you need to make a free body diagram of the pulley. A free body diagram is an object sitting in space and not moving hence the forces the pulley is experiencing must be balanced.

When some members say a single pulley only redirects a line pull they are failing to appreciate the forces imposed on where the pulley is attached. The load being pulled is only the tension in the line but the pulley's place of attachment is experiencing greater forces which can only be calculated by using Trigonometry and the angles each side of the line make with the pulley attachment.

Watch the TV series Rescue 401 and you often see heavy tow trucks with a pulley secured to the front of a disabled truck tractor and the winch line leaving the truck and going around the pulley and back to the tow truck.

If there was no increase in the forces applied to the disabled tractor, there would be no point in doing this.

Mounting the winch on the top of the boom pole avoids this doubling of the crushing forces the boom pole experiences.

Dave

 

[bcp]

But the winch is not anchored to the ground beside the load. It is usually at the base of the pole or boom and making maybe a 120 degree turn at the pulley. The cable is mostly parallel to the boom between the winch and pulley.

Bruce

 

[Dave_eng]

But the winch is not anchored to the ground beside the load. It is usually at the base of the pole or boom and making maybe a 120 degree turn at the pulley. The cable is mostly parallel to the boom between the winch and pulley.

Bruce

These concepts can be difficult and I am the first to admit my explanations can be too technical.

I did not suggest the winch was not anchored to the tractor as to do so would eliminate the maneuverability of the tractor which is why it is so useful.

Look at the pole NIW has built for his home construction. With the winch located at the top of the pole there is no issue with the forces exerted on the pole being any greater than the weight of the roof truss itself.

It is when the cable tension is redirected around a pulley at the top of the pole that the compressive forces on the pole start to be magnified.

Look on youtube. There are a number of videos on pulleys and their explanations may be clearer. You are looking for videos which describe a fixed pulley system.

Dave

 

[greenacresnorth]

Dave what you are confusing is dynamic and static loads, the 1200#'s you are quantifying are induced on the localized structure of the jib itself in a compression dynamic, the jib itself will only have to cantilever 600#'s. in the crane industry we measure in line pulls and structural/stability limitations. the fact that the hoist line passes over the point sheaves has no bearing on line pull or stability/structural limitations. our crane structures we design have static load sheaves and dynamic load sheaves, your upper point sheaves and running sheaves have a static load rating of line pull, where the lower sheaves where you would setup a multi part hook block are designed with max dynamic loads with a safety factor greater than the structural and stability limiting tables. now going back to your initial heeded warning, by affixing a winch to a gin pole or crane boom. you are correct in being cautious. without a calculated load rating table and a means to calculate our radii and total load on the fly, you could get yourself into trouble very quickly. 90% of all crane accidents are caused by operator induced instability. another 5% are caused by ground conditions, 2.5% by LMI/SLI malfunctions, and lastly the final 2.5% by acute structural failure.

 

[greenacresnorth]

Watch the TV series Rescue 401 and you often see heavy tow trucks with a pulley secured to the front of a disabled truck tractor and the winch line leaving the truck and going around the pulley and back to the tow truck.

If there was no increase in the forces applied to the disabled tractor, there would be no point in doing this.

the idea of this practice is to multiply applied force for a set amount of line pull. most heavy wrecker rotators are fixed at 40,000#'s of line pull, this is the safe working load for the 1" 6x37 RRL wire rope that is standard in the 25-40 ton class. they use snatch blocks to a) redirect the angles of force to flip a truck back over etc... b) multiply your pulling force without exceeding linepull of the hoist.

 

[bcp]

If someone wants to play with math, this might be useful.

Lifting Boom, Davits Application and Design Equations and Calculator

Application and Design Equations - Lifting booms also called davits Davits refer to single mechanical arms with a winch for lowering and raising objects.

www.engineersedge.com

Bruce

 

[Glassman13]

I used a boom pole with an electric remote 3000lb UTV winch on the end last year to lift and set all my trusses on my house it worked flawlessly and the remote on the winch allowed me to be on a ladder and set them by myself.
The trusses are not lightweight trusses either, 2x6 top and bottom cord 44 feet long and 9'6" tall.

View attachment 47942
View attachment 47943 View attachment 47944

Wow!! what a job that looks like . I thought my 3 beams for the carport was something but your house/ garage lifts are impressive. These tractors are hard working helpers for sure.

 

[Dave_eng]

the idea of this practice is to multiply applied force for a set amount of line pull. most heavy wrecker rotators are fixed at 40,000#'s of line pull, this is the safe working load for the 1" 6x37 RRL wire rope that is standard in the 25-40 ton class. they use snatch blocks to a) redirect the angles of force to flip a truck back over etc... b) multiply your pulling force without exceeding linepull of the hoist.

Any comments on the main issue being the compressive force in the pole?

Dave

 

[Russell King]

Any comments on the main issue being the compressive force in the pole?

Dave

The argument may be where the winch is attached...and where the pole is attached and where you evaluate the vertical reaction on the bucket.
I agree the pulley will be applying the 1200 pounds downward.

But I don’t understand the rest of the statement about the winch attachment versus a person on the ground. I guess if the winch is not on the base of the pole but below the attachment point of the pole the bucket sees 1200 pounds at base of pole, but if the winch is attached to the pole the bucket would see 600 pounds down net (1200 down minus 600 up). That may be what is being asked/stated.

 

[Dave_eng]

The argument may be where the winch is attached...and where the pole is attached and where you evaluate the vertical reaction on the bucket.
I agree the pulley will be applying the 1200 pounds downward.

But I don’t understand the rest of the statement about the winch attachment versus a person on the ground. I guess if the winch is not on the base of the pole but below the attachment point of the pole the bucket sees 1200 pounds at base of pole, but if the winch is attached to the pole the bucket would see 600 pounds down net (1200 down minus 600 up). That may be what is being asked/stated.

I was just trying to get Glassman13 to broaden his comments. He focused on my pulley example but not the real question of the forces on the pole not the FEL.

Comp[ressive forces as the pole would experience are the type where failure can occur with little to no warning unlike a structural memeber being bent sideways

Dave

 

[Glassman13]

to Dave-eng, I was only complimenting a job well done. As the technical details you are having here I'm not a math person. I may have in rookie innocence blundered here, my apology if so.

 

[greenacresnorth]

Any comments on the main issue being the compressive force in the pole?

Dave

compressive forces are relative to the dynamic loading of the structure and relative boom angle. for every unit of weight lifted the compressive load on the pole will be multiplied exponentially with relation to angle of deviation. a flat boom with close to 90* of from pole moment arm to wire rope running angle will decrease compressive load compared to a near vertical boom.

 

[skeets]

DAYUM WOLFMAN I am impressed !!!

 

[PaulL]

If you raise the 600 lbs using a winch attached to the tractor or loader frame, the tension on the winch side is between the winch and the pulley, not between the pulley and the ground, hence only 600 lbs is seen by the FEL.

I think to be more specific, if you have a pulley on the pallet forks, and 600# on one side, you have to have 600# pulling on the other side as well. 1200# total.

If the winch is on the tractor, the tractor front wheels only see the 600#. There's 600# load, 600# pulling on the other side of the pulley, and 600# pulling upwards on the winch/tractor. Wheels see only the load. But the FEL is seeing 1200#, there's 600# pulling up on the tractor frame.

If the winch is on the pallet forks though, then the loader is now only seeing 600#. And thinking about it, it'd be kinda crazy to put the winch anywhere but on the pallet forks, otherwise when you lifted the FEL up and down the load would run through the pulley. Works fine with an electric winch, with a manual winch it'd be hard to let it up and down without standing on the pallet forks.