Quadcopter

A quadcopter, also called a quadrotor helicopter or quadrotor, is a multirotor helicopter that is lifted and propelled by four rotors. Quadcopters are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is generated by a set of rotors (vertically oriented propellers).

Quadcopters generally use two pairs of identical fixed pitched propellers; two clockwise (CW) and two counter-clockwise (CCW). These use independent variation of the speed of each rotor to achieve control. By changing the speed of each rotor it is possible to specifically generate a desired total thrust; to locate for the centre of thrust both laterally and longitudinally; and to create a desired total torque, or turning force.

Quadcopters differ from conventional helicopters which use rotors which are able to vary the pitch of their blades dynamically as they move around the rotor hub. In the early days of flight, quadcopters (then referred to as 'quadrotors') were seen as possible solutions to some of the persistent problems in vertical flight; torque-induced control issues (as well as efficiency issues originating from the tail rotor, which generates no useful lift) can be eliminated by counter-rotation and the relatively short blades are much easier to construct. A number of manned designs appeared in the 1920s and 1930s. These vehicles were among the first successful heavier-than-air vertical take off and landing (VTOL) vehicles. However, early prototypes suffered from poor performance, and latter prototypes required too much pilot work load, due to poor stability augmentation and limited control authority.

Quad (play)

Quad is a television play by Samuel Beckett, written and first produced and broadcast in 1981. It first appeared in print in 1984 (Faber and Faber) where the work is described as "[a] piece for four players, light and percussion" and has also been called a "ballet for four people."

It consists of four actors dressed in robes, hunched and silently walking around and diagonally across a square stage in fixed patterns, alternately entering and exiting. Each actor wears a distinct colored robe (white, red, blue, yellow), and is accompanied by a distinct percussion instrument (leitmotif). The actors walk in sync (except when entering or exiting), always on one of four rotationally symmetric paths (e.g., when one actor is at a corner, so are all others; when one actor crosses the stage, all do so together, etc.), and never touch – when walking around the stage, they move in the same direction, while when crossing the stage diagonally, where they would touch in the middle, they avoid the center area (walking around it, always clockwise or always anti-clockwise, depending on the production). In the original production, the play was first performed once, and then, after a pause, an abbreviated version is performed a second time, this time in black and white and without musical accompaniment. These are distinguished as Quad I and Quad II, though Quad II does not appear in print.

Quad (music)

Quad or QUAD was the name of a solo music project by Gary Ramon.

During his six-year hiatus from Sun Dial, Ramon embarked on an ambitious solo project, Quad, which combined ambient electronica with kraut rock. The result was a pair of self-titled albums. The first of these was released on Ramon's own Acme Records in 1997 as a 1000-copy limited edition on 12" clear vinyl with a transparent sleeve. The second Quad album was released in 1998 on the Prescription label as a 99-copy limited edition LP.

A 1999 American re-release of the first album on CD and 10" LP on the Man's Ruin label was scheduled, but eventually cancelled.

Both albums are now highly sought-after collectors' items.

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Quad (rocket)

In rocketry, the Armadillo Aerospace Quad vehicle called Pixel is a computer controlled VTVL rocket that was used in 2006 to compete in the Lunar Lander Challenge.

General description

The quad vehicle design is a pressure fed in blow-down mode from an initial pressure of 320 psi for level 1 (400 psi level 2). The cold gas vernier engines are cross-fed by gas drawn from ullage space of the opposite tank. The vehicle was able to transfer propellant through connecting pipes between opposite tanks by controlling ullage pressures with the thrusters; this helps it balance, minimizing gas use. The main engine had two-axis thrust vectoring. The vehicle was fully computer controlled; with guidance from GPS and fiber optic gyros.

Specification

The specification for Pixel/Texel for level 1: