Overhead Crane – Ver2 – I

I posted my work on my Overhead Crane (original single girder bridge beam) to Railroad Line Forums. Russ Greene .. owner of NE Brownstone posted back with photos of overhead cranes and I was caught by the dual bridge girder designs and desided I could modify my original design to make one of these.
Overhead  bridge crane -1One photo that jumped out at me is the one to the left. It has a very nice layout of a dual-girder/bridge crane. Not only does it layout everything so nicely but it gives me the correct terms for everything.

While mine will be much .. much backdated from this newer version I can use it as a guide.

Image1We also have this one of a massive overhead winch assembly with shafts and gears and whatnot .. which really looks cool. Again .. mine will differ .. well completely .. being crane blocks and a winch but again .. as a guide it works great.
Dual Bridge Crane
working_2-800I lengthened the truck from my earlier crane so it would support two bridge girders. I added a third wheel to the center of the truck .. just seemed to me that it needed one there. I also switched the location of the spur gears so the smaller one is on the pulley shaft.

The trolley will be next. The intention is that is will also be moved via a pulley. I don’t want that chain to hang down where the hook would pick up the load .. it really needs to be off to one side. I think .. another pulley shaft but say .. square. This could be a sliding fit in the trolley mechanism and fixed on both ends at a pulley so both pulley chains would hang close to each other. If nothing else it adds to the complexity and “steam punkish” look I like.

blockbracket-800I started by modifying the bracket I had made up for the single girder crane so that it is just a cast bracket with a couple of shoulders to mount to the trolley somewhere. This is still early in the design and tentative at best.
trolley_working_1-800The gearing for the trolley is taken directly from a chain hoist. I colored the bits and pieces simply so I would un-confuse myself a little as to what is what. The pink shaft will mount the hand chain. The thing gives a 30:1 ratio. The driven side spins that cable drum (blue) which takes the cable from the anchor block.

questions to be answered .. or at least faked ..

1 – the three-sheave block with the one below it gives a 6:1 ratio. With the trolley at 30:1 that gives a 180:1 ratio. I may have to go to block with less sheaves.. a 2 sheave block (and it’s buddy) would give a 120:1 ratio .. and a pair of single sheave blocks would still give a 60:1 ratio. Right now I am looking at a chain hanging from the trolley about 15ft. long .. say one rotation about 36ft. If I leave the 180:1 ratio .. to raise something 10ft would require some guy moving 1800 ft. of chain .. or .. moving that hoist chain 50 complete rotations. Reducing the blocks to two sheaves would .. as I said .. make the ratio 120:1 .. and require 30 complete spins of the hoist chain. What fun. 🙂

2- need to figure how large the cable drum needs to be. It has to be at minimum six times the maximum movement of the hook hanging from the lower/load block. The drum size determines where it fits in relation to everything since the gears have to mesh. That sets the height of the trolley mechanism .. which in turn sets the height of the anchor block .. blah blah. Once all that is determined I can construct a trolley body to hold all those bits.

trolley_working_2-800This thing is NOT very big .. which can be seen when it is placed in context with a piece of On30 track, some wooden crane beams and a NMRA On3/On30 Clearance Gauge. That is about 18ft. high .. which is the maximum that the crane hook will move .. so .. 6 x 18 = 108ft. that cable drum needs to hold.
– Well … that’s not going to work
drum-testYou gotta understand that when I am modeling, a large part of it is that I see it as art .. and I approach that modeling from that point .. what looks ‘cool’ and interesting. To hod myself back and apply at least a modicum of control I try and to see how I can make ‘whatever’ work .. real world.

I had thought that .. hanging a block off of a trolley with a cable drum would look cool. It would .. but there is a reason this wasn’t done (insert – much, never etc.). In the meanwhile .. while doing this I found an interesting webpage at Ingersoll Rand – a nifty Ingersoll Rand Drum Capacity Estimator .. pretty useful for sure for us scratchbuilders.

What I hadn’t considered is that there is something they call the ‘Fleet Angle’. This is the angle from the fixed sheave to the drum flanges and is 1/2 to 1-1/2 deg. for a smooth drum .. which in turn means that depending on the width of the drum you have a minimum distance from the sheave to the drum. I played with the numbers for a while. With a Barrel diameter of 9 in. .. a flange diameter of 28 in. .. ad a Drum length of 2 in. ; using 5/8 in. cable (.35mm beading wire) I could get my 108 ft capacity I needed and even the D/d ratio is ok.

The problem being though that this gives a minimum distance sheave to drum of 4 ft. I played around with this a bit and could stick the drum up on top and get the 4 ft. distance needed but if you look at the drawing this pretty much limits the movement of the trolley to about six ft from the end of the bridge beams.

Oh well. That’s why everyone went with the geared winch’ey trolley (think chain pulley) ..

Still found out a bunch about cable drums, cables, fleet angles etc. Good stuff.


Overhead Crane – Ver2 – I — 1 Comment

  1. Looks really neat Ed. Your commitment to detail is unbelievable.

    Looking forward to this being finished.

    Is this going to be used on the RR??


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