Questions for structural/mechanical engineer-types re workpiece positioning device

This is not just for engineers, anyone is welcome to chime in

I've been asked to study/possibly build a special load-positioning device for use with a knuckle-boom crane.

Below are two simple drawings.

In the upper drawing, the knuckle-boom crane is carrying a piece of pipe 20 feet long and weighs 3,000 lbs. The pipe is suspended by chain. This arraingement cannot get the pipe into the required position.

In the lower drawing, the same pipe is perched atop a (proposed) 3-axis load-positioner and sits 4 feet above the centerline of the crane. All motion is hydraulically controlled and allows for precise positioning of the pipe.

The crane is rated 6,000 lbs at this distance. The positioner would not have any manufacturer's data affixed to it, nor even available. The work area, of course, would be coned and roped-off.

Assuming the load is well-balanced and properly handled, is the crane subject to any abnormal forces or potential damage in any way?

Would a construction-site safety man or an OSHA rep freak out if they saw this?

Do you see any reason why this device would not work, or would be dis-allowed on a jobsite?

Please note: I am not looking for alternative means of lifting/positioning the pipe - only input regarding using a crane in a way that is maybe a little out of the ordinary. THANKS

You custom "work lifting device" will need the same "approvals as any other hoist, sling, or chain. Else expect flack from OSHA. And if something went screwy, Hell to pay.

Also, The ridged in torsion nature of your attachment totally screws any "rating" for the present boom. That is, an off balance load lift is entirely undetermined, because you don't know the forces.

I wouldn't do it if I wanted to "play it safe", but ...........when has that ever stopped anything?

X 2 on balance (though not as well described as CalG )

I think balance would be your main problem - if something's hanging from a hook it can swing and ''find it's own balance'' without causing any twist etc in the boom, IMO your proposed method would only have to be a gnats out to cause problems.

I would worry about the moment that the pipe is now placing on the boom. This would be a serious no-no for a lattice boom crane. However it being a knuckle boom it should be fine. With all the sue happy lawyers in the world it would make me scared.

i suspect that any truck mounted knuckle boom crane would not have a 3000 lb rating out that far. I have a friend who had a 4500 lb Hiab on a small flat bed just like that. with that extension maybe you could pick 500 lbs. even with the out riggers down, even a small load bobbing around would easily tip the truck. Leverage is working against you here. We were once picking a 3500 lb press. we had to get the press right tight with the side of the truck and we were just able to work it up onto the truck.

It's amazing what you find on You Tube. Contact the Pipe lifter company and see if they have a model for a truck. I would think they would with a boom truck with outriggers. https://www.youtube.com/watch?v=BY0mVZUFccg

https://www.youtube.com/watch?v=V9HnVH4gQ1M

Limy Sami said:

X 2 on balance (though not as well described as CalG )

I think balance would be your main problem - if something's hanging from a hook it can swing and ''find it's own balance'' without causing any twist etc in the boom, IMO your proposed method would only have to be a gnats out to cause problems.

Click to expand...

The pipe would have the balance point fairly-closely identified, plus the positioner will have a hydraulicly-powered lateral adjustment (specifically for balance).

All hydraulic and crane functions are by remote control, and the operator would be right there watching. Out-of-balance conditions would be easy to spot and correct.

The positioner would likely be much safer than using a forklift (or two) and hand signals, etc.

Ringleboy26 said:

I would worry about the moment that the pipe is now placing on the boom. This would be a serious no-no for a lattice boom crane. However it being a knuckle boom it should be fine. With all the sue happy lawyers in the world it would make me scared.

Click to expand...

I agree on the moment, which is why we would build in 3-axis, plus lateral movement along one axis. The knuckle-boom crane has a lot of moving parts and slop everywhere, along with replaceable wear pads. I doubt it would hurt anything, as long as the load was well within the load range.

Re the sue happy: can't do anything about it, so why worry about it? If you get sued, you're gonna' turn it over to your insurance company and from that point, you have no say in the matter.

surplusjohn said:

i suspect that any truck mounted knuckle boom crane would not have a 3000 lb rating out that far. I have a friend who had a 4500 lb Hiab on a small flat bed just like that. with that extension maybe you could pick 500 lbs. even with the out riggers down, even a small load bobbing around would easily tip the truck. Leverage is working against you here. We were once picking a 3500 lb press. we had to get the press right tight with the side of the truck and we were just able to work it up onto the truck.

Click to expand...

They make k-b cranes that will lift 3,000 lbs at 100+ feet. The operating distance for this customer varies, but the load will likely always be less than half the limit of the crane (due to concerns about moment).

Those cranes get a lot of torture when a load swings or is bounced, but they're made for it. Explaining it to a government employee might be difficult!

Looks allot like a rotator on the working end of a standard logging truck....need more capacity ?
Look up the very similar trucks the railroads use in setting rail, and general R.O.W.
Maintenance.

Ringleboy26 said:

I would worry about the moment that the pipe is now placing on the boom. This would be a serious no-no for a lattice boom crane. However it being a knuckle boom it should be fine. With all the sue happy lawyers in the world it would make me scared.

Click to expand...

I was coming in here to put the exact same thing, you are now introducing torsion to the crane boom and locking up some degrees of freedom on that load.