|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.|
One 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.
|We 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.|
|– Well … that’s not going to work|
You 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.