** I apologize up front for what looks like a redundant post. This post was meant primarily for a video. However, it appears that mocpages has changed its policy once again, and now is not allowing applets. Therefore one cannot post youtube vids, at least not to my knowledge. First iframes and now no applets, what next?? So for now, embedding the videos by hyperlink is the only way to view the vids I discuss here. Please view vids for complete information and reason for the post. If anyone knows a way around this, please PM me or post it on this post. Truly, the reason for this post was to show a success over a previous failure, best demonstrated by video. **
About this creation
Euroricks.com is having a crane competition, and well, that got me playing with the model I made a year or so ago. I love cranes, I think their concept is so prehistoric, just a bunch of cables holding everything up. Sometimes I think all the cables, lines, pulleys and winches almost look Rube Goldberg-like; except, unlike a Rube Goldberg machine all the fanfare is completely functional. Cranes can lift thousands of tons, all with physics, cables, pulleys, and the like.
Here is my model (previous versions can be found perusing my pages), but I redid the Y-guy arrangement so it is more accurate and stronger. About a year ago I tried to lift the 8070 supercar (my version, which is a little heavier at 1433 grams), and failed. RebrickableLEGO (youtube) tried as well but also failed (ultimately they did with their actuators, which is NOT how cranes work). First two attempts, RebrickableLEGO’s and mine, are here
Well, I am too stubborn. All this crane talk got me re-interested, and I was bound and determined to make the lift. Installed a large motor (used to have M PF motor) and more pulleys. The pulleys are true pulleys. Funny, on Bricklink.com these are called pulleys, but the main benefit of pulleys lies in their multiplicity. Really, you can’t add lots of these pieces to increase lifting ability because they have to move independent of each other, which they cannot do when all linked by an axle.
A true pulley looks like those available on shapeways.com by Efferman.
Check out the video, lifted the 8070 supercar just fine.
Here are some pics of the crane lifting other things…..cranes are awesome!
Kinda reminds me of:
The improved “Y guy” arrangement allowed me to lift things to great heights even with the boom completely extended.
Thanks for looking and remember to rate and comment!
Good demonstration of the fundamentals of block and tackle design -- especially the need to decouple the individual sheaves (pulley wheels). The most important parameter is the total number of cables N supporting the moving (here, lower) block. When 1 cable connects the winch to the fixed (here, upper) block, the load/winch cable speed ratio is 1/N in the absence of stretch. As explained on the Wikipedia "block and tackle" page, the mechanical advantage (ratio of load weight to winch cable tension) is N less a penalty due to friction in the winch and sheaves.