TOWER CRANES

Here’s a typical tower crane.
The main parts are the

tower jib (boom) and counter-jib counter weight and pendants and here’s my first attempt.

The crane is built from 1×3 pine, lots of 1/4″ carriage bolts, a heavy duty swivel bracket and miscellaneous hardware.

Torque is computed as Weight (or Force) times Distance. If you’ve forgotten, go back to the crane videos.

We didn’t have a way to move the load along the length of the jib, so we hung the load from a dowel positioned closer in along the jib.

We need a trolley. Real tower cranes use a trolley to move the load along the length of the jib.

The trolley (in red) hangs from the underside of the jib and the pulley block is attached to the trolley. You can see the line going from the trolley to the tip of the jib and also the line going back to the drive motor on the machinery deck.

The pulley and turn-buckle set-up did not work well, so I made a new system using bike parts- chain and 2 sprockets.

When the trolley moved in, the load automatically descended so I had to come up with an improvement to the tower crane trolley system. Billy Maguire (with Morrow Cranes in Salem OR) sent me a diagram showing how it’s done on a real crane.

The trolley is controlled by a simple arrangement- there’s a line attached to the J hook mounted on 1 end of the trolley ( the black plywood). This line runs to the 2 sheaves (pulley wheel) mounted at the end of the jib-then back to the windlass ( I wrapped some sandpaper around the axle to prevent the line from slipping)- then on to the other j hook.

So much for the trolley. Now the load line-starts off tied to the eye bolt attached at the end of the jib- then runs through a small single sheave pulley screwed to the front of the trolley- then down to the lifting pulley, and up and through the 2nd single sheave pulley- finally through 3 more sheaves on its’ way to the windlass.

Now the 2 lines are separated and the trolley is not affected by the load line.