Why does a delta move so much faster than a normal arm?

The motors sit on the fixed base, so the moving arms and platform carry almost no motor mass. Less inertia to accelerate means the tool can start, stop, and change direction quickly. The speed comes from the geometry.

Can a delta do anything a six-axis arm can?

No. A basic delta gives three translations plus an optional wrist rotation, and it works a small shallow dome. If you need to reach around a part, approach from odd angles, or cover a large envelope, that is a serial arm's job. Deltas are specialists for fast picking of light parts.

Why are deltas usually mounted upside down over a line?

The work zone is a dome that opens downward from the base plate. Hanging the robot above a conveyor puts that dome right over the parts, so the tool reaches straight down into the flow. It is the natural orientation for the geometry.

Robot types

Delta Robot

A delta robot is a parallel-kinematic machine whose end-effector hangs from three arms driven by three base-mounted motors, giving very fast, light pick-and-place motion.

What it is

A delta robot is a parallel-linkage design. Three arms connect a fixed base plate to a small moving platform, and each arm is driven by its own motor mounted up on the base. The payload rides on the moving platform, usually with a compact end-of-arm tool for picking.

Because the heavy motors stay bolted to the frame instead of riding along the arms, the moving mass is tiny. That is the whole point of the geometry: keep the arms light so the tool can whip through a cycle without much inertia fighting it.

How it actually works

Each of the three motors swings an upper arm through an angle, and paired parallelogram forearms link that upper arm to the moving platform, holding the platform's orientation fixed while its position changes. Coordinate all three angles and the platform reaches any point inside a shallow dome-shaped work zone. Three motors give three translational degrees of freedom; a fourth axis, often a central shaft running down to the tool, adds rotation about the vertical when the job needs it.

The design shows up in high-speed sorting and packaging. The FANUC DR-3iB delta is built for exactly that kind of duty, mounted overhead above a conveyor and reaching down into the work zone below it. Cycle rates come from the low moving mass.

How it differs

Serial (articulated) arm · A standard six-axis arm is a serial chain: each joint carries the weight of every joint past it, so the motors get heavier toward the base and the arm has real inertia. A delta is parallel: three closed loops share the load, motors stay on the base, and the moving structure is featherweight. The tradeoff is reach and dexterity. A serial arm can approach from many angles across a large envelope; a delta gives up that flexibility to win speed inside a small dome.
SCARA · Both target fast pick-and-place, but a SCARA is a serial arm with a rigid vertical Z and jointed horizontal reach, while a delta is a parallel mechanism working an overhead dome. A SCARA plants on a bench and reaches out; a delta hangs above the line and reaches down.

Where you meet it in the field

FANUC DR-3iB · A production delta built for overhead high-speed picking and packaging.
ABB IRB 390 · A second delta platform, useful for comparing reach and payload class.

Common questions

Why does a delta move so much faster than a normal arm?: The motors sit on the fixed base, so the moving arms and platform carry almost no motor mass. Less inertia to accelerate means the tool can start, stop, and change direction quickly. The speed comes from the geometry.
Can a delta do anything a six-axis arm can?: No. A basic delta gives three translations plus an optional wrist rotation, and it works a small shallow dome. If you need to reach around a part, approach from odd angles, or cover a large envelope, that is a serial arm's job. Deltas are specialists for fast picking of light parts.
Why are deltas usually mounted upside down over a line?: The work zone is a dome that opens downward from the base plate. Hanging the robot above a conveyor puts that dome right over the parts, so the tool reaches straight down into the flow. It is the natural orientation for the geometry.