Pendulum maintenance bay · Velstraven

A small room of chapter 4. When you walk in, the room card reads: The pendulum arm swings free; its retaining pin stands out of its seat.

Narrated walkthrough

Pendulum maintenance bay from its entrance — Pendulum maintenance bay: how to solve it

Getting there

Chapter 4, third upper floor. The first room past the service gate east of the Lens-cleaning room, which opens once the stalled orrery is solved. Its east door leads to the Service galleries and reservoir hub, its south door to the Water-junction room.

What is wrong

"The pendulum arm swings free; its retaining pin stands out of its seat." The arm swings slowly from side to side, about 11–12 seconds per full swing. Only at the bracket end of each swing do the arm's pin hole and the bracket's line up, and only for a moment.

What you can work

Arm: The swinging pendulum arm. At the end of each swing its pad meets the bracket.
Eye: A fixed ring on the service bracket, a tether point.
Brake: A hand lever brake. Pressed, it stops the arm where it is; it springs off again after about four seconds.
Pin: The retaining pin. It goes through the arm and bracket only while their holes stay lined up.
Reading lamp: Optional light to read the room by: Handle toggles it, Heat lights it, Supply liquid douses it, Place light roots a lasting flame blossom in its cup. It works none of the room's fittings.
Reading shutter: Optional: Handle or Orient opens a high window for daylight from a second angle. It works none of the room's fittings.

Solution

A nudge

The brake stops the arm dead wherever it is. Only now can a spell steer it, and you have about four seconds.

The full solution

Handle the Brake.
The brake stops the arm dead wherever it is. Only now can a spell steer it, and you have about four seconds.
What you see: "The inspection brake holds while its hand lever is depressed."
Straight away, aim at the Arm and cast Orient (Water, Will, Will).
With the arm held still, Orient swings it round to the bracket.
What you see: "The supported arm turns toward the service bracket."
Before the brake springs off, aim at the Eye and cast Tether (Growth, Growth, Will).
A short line from the bracket eye stops the arm swinging back, so it stays put without the brake.
What you see: "The line opposes the pendulum's return from its service endpoint." The arm reads "A taut line holds it at the bracket."
Handle the Pin.
The arm is held still at the bracket, so the two holes stay lined up.
What you see: "The pin seats through both holes and carries the arm." then "Pendulum maintenance bay settled."

Other ways that work

By hand, no spells: stand at the Pin and keep pressing Handle as the arm swings toward the bracket. In the instant it pauses there, before swinging back, the holes line up and the pin goes in. The pause lasts a bit over a second, once per full swing.
Anchor (Growth, Growth, Water) on the Arm just as its pad reaches the bracket. No brake is needed: "A root cuff grips the contacting service pads." Then Handle the Pin.

Watch for

Pressing the Brake mid-swing stops the arm there. When it springs off, the arm swings only as far as where it stopped, so it may never reach the bracket again. To fix it, brake and Orient the arm to the bracket (that restores a full swing), or restart the room.
Orient without the brake is refused: "…its swing carries it past the push; it can be steered only while something stops it."
Tether only reaches once the arm is braked at the bracket: "The short maintenance line cannot reach tautly until the arm is held beside its endpoint."
Pressing the Brake again while it holds releases it.
A Stilling ward under the arm does not help here. Its drag bleeds the swing until the arm falls short of the bracket.
Early presses on the pin just refuse ("The two pin holes do not stay aligned."), so it is safe to keep pressing.

If it goes wrong

There is no failed state, but a badly timed brake can leave the arm swinging too short. Brake and Orient it, or restart.
Hold R for one second ("Keep holding to restart from the room's autosave"), or use the pause door "Restart from autosave", to put the room back as it was when you walked in: "Automatic room-entry save restored." Rooms you settled earlier stay settled.

Achievements here

Pendulum Tamed: Solve the Pendulum maintenance bay.
Steady Hands: Steady Hands: settle this room without a spell taking effect here. Any cast that takes hold in the room counts against you, including one at the reading lamp or a cast on yourself. Use the by-hand route: stand at the Pin, watch the arm come toward the bracket and keep pressing Handle until the pin seats. Don't touch the Brake unless the arm is already at the bracket. If a spell does go off here by mistake, restarting from the room's autosave also restores your achievement record from when you entered.
Set and Hold: Set and Hold: Handle the Brake, Orient the Arm, then cast Anchor on the Arm within 20 seconds. It then sits at the bracket, so the cuff takes.

Spells used

Orient, Tether, Anchor.