What Is a Coreless Motor?

A coreless motor (ironless motor) uses a self-supporting cup-shaped winding without an iron core as its rotor — the copper cylinder itself spins in the magnetic field. Removing the iron eliminates iron losses and cogging torque, cuts rotor inertia by roughly an order of magnitude versus an iron-core motor of the same size, and pushes the electrical time constant below 1 ms for very fast start-stop response.

Why Dexterous Hands Use Coreless Motors

A dexterous hand finger has only 10–20 mm of diameter to work with, yet must grasp at high frequency:

• Compact: a 4–16 mm coreless motor plus a micro planetary gearbox or leadscrew drives one finger;
• Low inertia, fast response: finger open/close cycles of several Hz are achievable;
• No cogging: smooth grasp force, better fingertip force control;
• Efficient: typically 70%–90%, important with the limited heat dissipation inside a palm.

The trade-off: the cup winding dissipates heat poorly and tolerates little overload — continuous torque sits in the mN·m range, so a high gear ratio is mandatory for usable grip force.

Coreless vs. Frameless Torque Motor: Division of Labor

One-line split: coreless for fingers, frameless torque motors for arm and leg joints. BXI's 85/70/50-series joint actuators take the frameless-motor-plus-planetary quasi-direct-drive route for high-torque limbs, complementing coreless-driven hands at the end effector.