SWING RADIUS · CLEARANCE PLAN
LOAD CELL1.00 g
1.45 gPEAK 1.00
- CABLE
- 7.0 m
- PERIOD
- 5.3 s
- SWAY
- 0.0°
- TROLLEY
- -58 m
- WIND
- 0.0 m/s
GANTRY
A crane is a stick and a string. Four 2.4-tonne counterweights are stacked on the quay and they have to end up on four roofs a hundred and thirty metres apart, over a street that is full of things you cannot hit: a site bridge, a tower crane's jib, an access tower — and the rope itself, which has to get past all of it too.
Traverse to move the trolley. Hoist to change the rope, and the rope is your altitude. The load is a pendulum on the end of it: it swings because you moved, and it keeps swinging after you stop.
The load is hanging.
The trolley, the rope, the clock and the block are all exactly where you left them.
Two controls and a pendulum.
- A / D · ← →
- Traverse the trolley along the rail. It accelerates slowly and coasts to a stop — that is what makes it controllable.
- W / S · ↑ ↓
- Hoist up and pay out. Rope length is your altitude, and it sets the swing: a 7 m rope beats in 5.3 seconds, a 26 m rope takes 10.2.
- SHIFT
- Precision. Less speed, less acceleration, and a much gentler load cell.
- SPACE / E
- Take the load off a block, or set it down inside the ring on a deck. The ring has to be lit and the load has to be still.
- ESC · H · M · R
- Pause, these notes, mute, restart the shift.
Killing a swing
You cannot brake the load. You can chase it: drive the trolley under the load, then stop. Every overshoot adds to the swing; every correct move takes energy out of it. Two or three passes and the block is dead still.
Things that will end the shift
Steel, decks, and the rope. A load over the block hits the facade; a load under the site bridge puts the rope straight through it, because the trolley is above the bridge and the rope has to cross it. The clearance plan in the corner draws the swing ring and lights anything the ring can reach — including the line of the rope.
The load cell reads tension, not motion. Standing still is 1.00 g. Every swing adds v²/Lg on top, and a heavy snatch takes it over the limit fast enough to cost you the shift.
FOUR ON THE DECK
Every counterweight is chained off.