Exercise 14: A cable that hangs and sways

Purpose. To hang a cable between two posts, so that it sags, sways in the wind and swings when a post is moved.

A beam, as in Exercise 8, is a straight band between two points. A cable has weight. It droops between its ends, and when an end moves the rest follows late and swings. The Rope emitter makes a line that behaves that way.

Before starting

• Two ordinary Parts named PostA and PostB stand about 20 studs apart, tops at the same height.
• One new Part named Cable sits at the top of PostA, with Size 0.3, 0.3, 1 and a dark colour. Its size sets how thick the rope is.

Procedure

Steps 1, 2, 5 and 6 repeat earlier exercises.

Step	Control	Action	Result
1	Cable	Select. Press ▾ beside Transform, then Transform as Rope.	Cable turns invisible. The Emit box reads 1.
2	HUD ▸ Emit button	Press	A rope 12 studs long appears, fixed at Cable by one end. It swings down, hangs, and vanishes after two seconds.
3	Properties ▸ Spawn ▸ End Anchor ▸ *	Press. Click PostB. Press Set.	The End Anchor row shows the path to PostB.
4	HUD ▸ Emit button	Press	A rope appears between Cable and PostB, with a gentle sag in the middle. It vanishes after two seconds.
5	Properties ▸ Emission ▸ Mode	Set to Animate	The Loop row appears.
6	Properties ▸ Emission ▸ Loop	Switch on	The rope appears and stays.
7	PostB	Select it and drag it a few studs, then select Cable again	The end of the rope goes with PostB. The rest follows a moment later and swings before it settles.
8	Properties ▸ Rope ▸ Wind	Enter 2, 5	From the next cycle the rope sways from side to side.
9	Properties ▸ Rope ▸ Slack	Enter 1.5	From the next cycle the rope is longer and hangs in a deep loop.

NOTE

A rope does not collide with anything. It passes through parts and through the floor, and it has no On Hit event.

NOTE

The length of a rope is fixed when the rope is made. If its ends are then pulled apart, the rope goes taut and stretches. It does not grow.

What the steps did

A Rope emitter makes a chain of segments from a start to an end. The start is the emitter Part. One particle is one whole rope. Each segment is a duplicate of the Part, stretched to fit.

At step 2 there was no End Anchor, so the far end was free and the rope hung from its start alone. At step 4 the far end was fixed to PostB.

In Emit mode a rope lives for its Lifetime and is gone. A cable that should stay is made in Animate mode with Loop on, as the glow of Exercise 6 was. The rope keeps its pose from one cycle to the next, and picks up edits at the start of each cycle.

Row	Starts at	What it sets
Spawn ▸ Pin Mode	BothEnds	Which ends are fixed. BothEnds fixes the far end to the End Anchor. StartOnly leaves it free. Launch throws it.
Spawn ▸ End Anchor	None	The object the far end is fixed to, or thrown at.
Rope ▸ Segments	12	How many pieces the rope has. More pieces give a smoother line and cost more. At most 48.
Rope ▸ Rope Length	0	The length in studs. At 0 the length is worked out from the gap between the ends.
Rope ▸ Slack	1.2	Used when Rope Length is 0. The rope is this many times as long as the gap. At 1 it is taut.
Rope ▸ Gravity	0, -40, 0	The pull on the rope.
Rope ▸ Wind	0	The strength of a sideways gust that ripples along the rope.
Rope ▸ Damping	0.03	How quickly a swing dies down.

With Cable 20 studs from the centre of PostB and Slack at 1.2, the rope is 24 studs long, in twelve segments of 2 studs. With no End Anchor and Rope Length at 0, the rope is 10 times Slack: 12 studs.

If the result differs

Symptom	Cause	Action
The rope hangs from Cable only	The End Anchor row is empty.	Repeat step 3.
The rope is a straight, tight line	Slack is 1, or the posts were moved apart after the rope was made.	Raise Slack. In Animate mode, wait for the next cycle.
The rope pulses or reels in every two seconds	Grow In or Death Mode is set, and replays at every cycle.	Set Grow In to 0 and Death Mode to None.
The rope looks like a row of separate blocks	The segments are thick and few.	Lower the Thickness graph in Appearance, or raise Segments.
An edit does nothing	In Animate mode an edit waits for the next cycle.	Wait up to one Lifetime.

Variations

Change	Result
Mode Emit, Pin Mode Launch, Motion ▸ Launch Speed 80	The far end is thrown at PostB, reaches it a quarter of a second later, and attaches: a grappling line.
Emission ▸ Death Mode Retract, in Emit mode	At the end of its life the rope reels itself in.
Emission ▸ Death Mode Release, in Emit mode	At the end of its life both ends let go, and the rope falls.
Pin Mode StartOnly, Appearance ▸ Taper, a graph from 1 to 0.15	A whip that thins toward its tip.
Rope ▸ Bend Stiffness 0.6, Gravity 0, 10, 0	A stiff tendril that floats upward.
A Light emitter with Emit 1 inside the Rope RenderTemplate	Every segment carries a light: a glowing cable.

Log

New in this exercise	Transform as Rope. End Anchor. Slack. Wind.
Done before	Transform as (Exercises 11, 12 and 13). Picking an instance with * (Exercise 7). Mode Animate and Loop (Exercise 6). The Emit button (eight times).
Carried forward	Nothing.