Jib Arm or Other Ideas?

Not sure the attic is design to hold that much weight. 3 tons is a lot to put in it.

Your head if it comes down. Just wouldn't set any over your bed. What rude awakening that would be.

Anyway why not just make a rail system. Hoist them up set them on the rail and push. If you can't put wheels on the speakers. Place them on flat cars on the track.

Ahh yes, I failed to mention in the OP - the 300 pound speakers are already installed. We are lifting them to remove them (and getting them out of the attic space is another story altogether).

Then, we replace each 300 pounder with a 120 pounder. Technology is wonderful. Better speaker, less weight.

And --- "hoist them up, set them on the rail" is exactly the issue... Hoist how??? One guy (video guys are always being waaaaay creative) suggested using a "giant electromagnet" on top of the roof, with a giant plate under the roof with a hoist on it... of course that can't work not because of the magnet fairy-tale, but because again - we can't get the plate up to the roof to stick to the underside in the first place. If we could get up there, reasonably and affordably, we would just attach to the steel that's already up there.

Next someone is going to ask "why not just use the suspension cables that are already in place?"

Because the existing cables are two 1/16" wire rope, no thimbles, single crosby clips installed backwards with the saddle on the dead horse, on what looks to be 1/4" rolled (not welded) eyebolts screwed into hangers shot into the pan deck and concrete.

We get calls like this all the time - "It's worked so far, and these have been here 15 years! They got put in even before the plaster went up before the building opened!!!" Except of course, they have not worked so far - half are dead, and they never gave the coverage needed. They just have not fallen so far. We call that different than "worked so far".

Forgot also to mention the catwalk weighs in at about 300 pounds per foot and runs almost 280 feet around the mezzanine.

Again, it's not the catwalk, or the building steel, that's giving us the fits. It's the budgetary impossibility of spending $300,000, and doing it in a week's time, to wreck the ceiling, hang the boxes, replace the ceiling...

This needs thought. You want to lift, swing the arm and travel along the arm?

While I think?

If there is any way, any way, any way, I can get the owner to let us have one for scrap, I would gladly launch one of these relics as far as we could throw it.

I'll paint one orange and see if we can get it launched at PunkinChunkin.

Physics Quiz For Saturday - what torque would be required, to achieve the acceleration required, to achieve the velocity required, to toss a $4000, 300 pound, 24x32x54 box the same distance as the Shortest trebuche shot at Punkin Chunkin last year?

I'll even wire up a battery powered amp and iPod so we can have the thing blasting Beethoven's 9th 4th Movement as it flies through the sky above the corn field!!! Video drama build up for first 3:18, loading 3:18 to 5:14 pensive crowd shots and mosaics of the operators getting everything set, skip forward to 12:58 AND LAUNCH with the Choral and Orchestra at about 108dB (at one meter) throughout the flight...

(off topic warning!!!) And if someone would build it, as fun as the speaker shot sounds, would it not be a lot more fun to launch a Ford Pinto or a Smaart Car???

All we need is a retired aircraft carrier launch mechanism, a little steam, a little space to set up...

Could you not use a block and tackle? Presumably, someone has to mount/attach a bracket in location on the ceiling structure for each speaker. It seems you could either mount a block attach point above that, or fabricate a block attachment to the speaker bracket. Then attach the upper block to that.

Yes, we could if we had a place to hang the B&T. See my notes in the OP about helium balloons, "skyhooks", holes in the roof... etc.

We use these instead of B&T unless the load is just a few pounds

http://www.cm-et.com/Public/29179/Lodestar.jpg

Thoughts/questions.

The base looks to be designed for a small angular swing, say limited by the angles of the gussets, outside those could cause apprehension.

The catwalk, I know that is not in the problem description, but prefabricated, punched steel ones wouldn't like the moment of the load out sideways at maximum arm.

The chain needs to be relatively unyielding and so must be the substrate of the catwalk.

I worry about the stability of these arms so my thought is toward the vertical pipe with an elbow to a horizontal pipe arm with a tee welded on the underside for the trolley. The vertical from the elbow could reduce to a pipe to fit inside the top of the main vertical.

To be continued...

I don't know if you mentioned access to rafters. I have used an electric winch hanging from a heavy gauge galvanized piece of pipe that I positioned between two rafters. It really depends on the rafters and the spacing but it might be very effective for 300 lbs.

I also was thinking about the kind of pulley based hoists that roofers set up on a flat roof. Some of those have a swing boom but you might need a few hundred lbs of counter weight. Having other roofers sit on the counter weight helped when we had really heavy loads. And fairly quick setup and tear down.

I would never use a winch as a hoist...ever! The braking and drum winding mechanism is not the same by any stretch of the imagination. Winches use dynamic brakes which must slide and are designed to do so. They are ineffective at holding hanging loads. If you use a winch in a vertical application, the load can back drive the gearbox as you try to feed the cable out (lowering the load) and cause an overrun situation which you can't stop. You'll kill some one. There are several reason's why every winch manufacturer clearly states that it's "NOT TO BE USED AS A HOIST". It's for horizontal pulling only (tow trucks, off-road recovery, etc).

"I have used an electric winch hanging from a heavy gauge galvanized piece of pipe..."

You shouldn't be given that kind of advice to anyone!. What's wrong with you?

Here's what happens when someone who does not know what they are doing uses a winch for a hoist -

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The workers were lowering the load, on a jib arm using a winch as the hoist, when the cable suddenly spun completely off the drum and the load fell 260 feet. Three of my workers were standing less than ten feet away when this happened (that's another story, the winch operators did not flag off the area, did not have a spotter or a person manning the tag line). Had the load not first smashed down on top of this speaker array which was hanging at about 140 feet

And pivoted about this shackle attachment and deflected about 20 feet on the way down (5/8" oval and attachment point both painted white the day before)

Then one of my guys would have been crushed under the falling load.

Reason number 10 jillion why TerraMan is dead-on right, and why we NEVER use anything but double-brake chain and cable hoists (not winches) which are specifically made for overhead lifting and for lifting humans. C/M, StageMaker, SkyClimber, etc.

Good point! Perhaps it was a poor choice of terms. I sometimes use the words engine and motor interchangeably but that hasn't caused any life threatening problems that I know of. A hoist is the correct device. If it can't hold a hanging load or lower a load under motor control then it is the wrong device.

Is there any reason a snorkel lift wouldn't work? No rental agencies nearby?

Can't run the basket of snorkel up through the plaster ceiling.

Can't get the lift in the room without making a $$$$ hole in a wall.

Even the new spyder lifts, which we have easy access to and use all the time,

like the JLG X700AJ

still can't get us up through the plaster.

Get six coolies and a sedan chair, I guess.

Can't you disassemble the speaker unit? I used to have a couple of Peavey 115 HT that weighed over 100lbs. But with the subwoofer and mid horn out it weighed 75. If they don't work, then you can cut up the cabinets too and viola! 300lbs gone.

If holes in the roof are acceptable, could you make a hole and have a "load plate" on the roof to distribute the weight? That might at least get you an overhead lift point(s).

How about an overhead I-beam trolley system? In my workshop I installed a Stanley roller system, it was good for everything I wanted to lift. The tracks were easy to mount, and the 4-wheel trolleys never jammed. I actually mounted two in an x/y axis system that covered all the workspace, delivered finished doors (200 lbs) to the exit.

If I am reading correctly this is a one-off job. The jib you show in the sketch seems to be over complicated and over engineered. Check out scaffolding poles and fittings. My sketch shows Kee-Clamp fittings and if you Google this you will find a locally available equivalent.

1 Your design rotates but you are going to reposition it for every lift. Why does it need to rotate? Just position the column at the rear of the walkway and fit the beam always at 90º from the walkway to over the speaker.

2 The column and base are designed to take bending forces without buckling. By using a tension wire at the rear of the beam you can eliminate bending and put the column into compression only. This allows a much lighter and simpler construction.

3 The blue strut is always in tension. Two wire guys, one to the centre and one to the end would achieve the same function with a much lighter beam.

I like the idea of using wire or something similar in tension (plate?) similar to standard engine lifts but...I'm not sure you can keep the post from bending at the bottom just by using wires.

The cable won't counter the moment load and the vertical post will break at the bottom joint.

Also, OP needs the chain block to roll in and out from the center post to the end of the boom (i-beam) 8 feet away. How would that work with a round tube?

Your concept is typical of a girder crane but keep in mind those have massive counter weights opposite to the boom. That's why they don't bend and break at the tower.

You are replacing a moment on the column and beam with a high axial compressive force, roughly, as you have drawn it, about six times the lifted load. Plus, he needs to move the load along the beam but has no trolley in your design. The moment will be there in the column because it must be welded to base members and they will be resisting the overturning moment, it will go into the column because that is stiff compared to the cable.

The pivoting is required because we have to maneuver in-between all the ceiling hanger wires, rotating left-right as we pull the hoist back to the catwalk.

Other thoughts were to make a rolling base and load it up with a huge amount of ballast - and we could manage about 2000 pounds of ballast and the catwalk can handle that. However, while this might solve the anchoring/base issue, it does not solve the boom-mast intersection problem.

To reduce the moment on the column, we can add a second boom and trolley as counterbalance. Trolley on green boom carries 400 pounds steel bricks - Standard 50 pound theatrical arbor weights. This will not equalize the load on both sides, of course.

Green Side = steel @ 400 pounds x 4 feet. Yellow Side = speaker @ 300 pounds x 8 feet.

I like 800 foot pounds out of balance a lot better than 2400.

Yes, the operator could slide the counterweights all the way out to the end, and with no load on the yellow boom, that might be bad.

That's why we would never allow anyone to use this device other than me, and one other highly skilled technician. We have to do this multiple times, but with a procedure and check list we can stay within certain limits. We will have to move the counterbalance as the load moves. We can even rig a cable system that moves the counterbalance as the load moves.

Thoughts? Better? Worse?

I like the counterweight better than the guy wires, especially if it can be moved in proportion to the speaker position.

I'm still suspicious of the base assembly and the catwalk construction. I smell trouble there. If the catwalk is made from expanded metal it might be too flexible. I would like to see a more positive hold down. The base must be designed for the appropriate moments in all of the directions that they can be applied.

The counterweight is much better than the cables. If the proportioned movement is too complicated for this operation, it could be static and provide half the moment of the lifted load. Half the load at an equal distance (the boom must be in place to lift the counterweight) or an equal weight split into at least two pieces at half the distance.

The biggest threaded pipe cross that I can find is a 4" dia. I thought one might be useful at the top of this Christmas Tree.

I would like to see a base clamped firmly to the catwalk with the bottom of the pole on a circular plate to rotate like a Lazy Susan on this base. It would need a way to anchor it to the base. Not sure how to do this. The base bothers me because flexibility increases the overturning moment.

I still like a pipe with a tee under it for the boom, The pipe brings torsional rigidity.

Sorry this is so bitty, I put it together at various short sessions.

I agree with Passington. The focus needs to be on properly anchor the thing to the catwalk. The jib crane itself can be designed in a dozen different ways. The issue is with the anchoring. Below is an example of IR's jib cranes. Very simple construction with no tie rod. They use an aluminum track slung under the boom to fit their tool balancer trolleys. You could copy the design without the aluminum track.

You need to consider the pivoting action in the design. If you just have an aluminium tube over another tube it will jam up as soon as you put load on it. You won't be able to swing it. The pics show a very simple roller bracket which rides the od of the tube. We built a few custom jib arms this way and it's pretty much industry standard.

Like I said, I think your biggest issue is the catwalk.

Can you post some pics of the catwalk so we can see what we're dealing with?