I've never heard of wireless servos but there are coreless types. Here's the difference explained between coreless motor and 3-5 pole (conventional motor). Taken from rcca's site.
Two types of motor are used to drive servos: multi-pole and coreless. Multi-pole motors are similar to traditional electric motors; they have three or five armature poles that act as miniature electromagnets. Five-pole motors are more accurate than three-pole ones, but both types have a property that coreless motors don’t have: when the armature is in a position that brings two poles within the field of one of the motor’s permanent magnets, it has less torque because the two poles “share” the magnetic field. This isn’t as much of a problem with an armature that spins constantly (such as your 24-degree stocker), but a servo motor might have to hold a position for a few seconds under load.
Coreless motors don’t have an armature in the same sense; instead, a lightweight woven basket of wire with a permanent magnet in the middle acts as the armature. This armature basket moves much faster than an iron-core armature, especially when changing direction. Such motors are also much more efficient than poled motors, but they generate more heat, and they’re more sensitive to shock.
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