What's Spinning? What's Pushing? Where Do the Magnets Go?
- Alisa Peters
- 3 days ago
- 4 min read
I've now written about magnetos (a rotating magnet generates current), dipole assemblies (a precisely engineered magnetic field moves particles through a gap), and read about hard drive read/write heads (a microscopic sensor sweeps across a spinning disc with extreme precision). At some point I realized that in all of these posts, something is moving, and I have been hand-waving past the mechanisms that actually create that motion. What is the rotor? What is an actuator? And how do magnets turn a static field into controlled, purposeful movement? Let's get into it.
For more background on who I am and why this post exists, head over to Introduction to Alisa Learns about Magnets.
💡 TLDR: What we’re covering
The Rotor and the Stator: The moving and stationary cores of rotational magnetic systems.
Actuators Defined: How mechanisms convert energy into both straight-line and precise angular motion.
The Invisible Engine: Why frictionless magnetic force scaling makes magnets uniquely fit for precision engineering.
The Rotor and the Stator
Every electric motor and every electrical generator, including the magneto, has two main structural parts:
The stator is the stationary part of the assembly. It is built directly into the outer housing and remains completely still.
The rotor is the rotating part of the assembly. It is the spinning component mounted on a central shaft inside the stator.
In a generator, you put in mechanical energy (turning the shaft) and get out electrical energy: a magnet on the rotor spins past coils of wire wound around the stator, inducing current through electromagnetic induction. This is exactly the magneto. The engine turns the shaft, the shaft turns the rotor, the spinning magnet induces current in the stator coils, and you get the voltage pulse that fires the spark plug.
In an electric motor, the process runs in reverse. Electrical energy goes in, and mechanical spinning comes out. The stator contains electromagnets. Current flows through them in a precisely timed sequence, creating a rotating magnetic field that pushes and pulls the permanent magnets mounted on the rotor. The rotor spins. This is how an EV's traction motor works, how a laptop cooling fan works, how a washing machine drum turns.
The Key Detail: The magnets on the rotor never physically touch the stator. Force is transmitted entirely across an air gap via magnetic fields. While the main shaft still rides on mechanical bearings, there is zero friction or wear at the actual point of electromagnetic energy transfer. With no physical components grinding against one another inside the gap, electric motors last vastly longer than internal combustion engines.
What's an Actuator?
While a rotor is strictly dedicated to continuous rotation, an actuator is a much broader term. An actuator is any mechanism that converts energy into controlled, deliberate motion. And that motion doesn't have to be a continuous circle.
Rotary actuator: Spins something in a controlled way. Functionally similar to a motor, but often used when precise angular positioning matters more than continuous rotation: opening a valve to a specific angle, rotating a camera mount, adjusting a control surface on an aircraft wing.
Linear actuator: Produces motion in a straight line rather than a circle. The powered seat in your car slides forward on a linear actuator. So does the arm that adjusts your side mirrors, the ram on a CNC machine tool, and the joints on industrial robot arms.
Voice coil actuator: A voice coil actuator has a permanent magnet inside a cylindrical housing, with a coil of wire (the "voice coil") that can slide in and out of the magnet's field. When current flows through the coil, it experiences a force pushing it into or out of the magnetic field. More current means more force. Reverse the current and you reverse the direction. The response is immediate, smooth, and extraordinarily precise.
Your phone's speaker relies on a linear voice coil actuator to pump a cone back and forth, which creates the sound waves. The read/write head in a hard drive utilizes a rotary voice coil actuator. This magnetic configuration allows a tiny sensor arm to swing back and forth across a spinning magnetic disc with micrometer or even nanometer-level precision, thousands of times per second, without overshooting or vibrating. The fundamental mechanism playing music through your earbuds is the exact same which is responsible for how cloud servers index global data.
Why Magnets, Specifically?
The unifying thread across rotors and actuators is this: magnetic fields exert force across a gap with no physical contact required. That property makes them uniquely suited to precision motion in a way that gears, belts, and mechanical linkages can't always match:
No friction at the point of force transfer: In a motor, the gap between rotor and stator is where the force happens, and nothing touches. That means no wear, no lubrication needed, and no mechanical degradation over millions of cycles.
Fast and repeatable: Magnetic force responds at the speed of electrical switching. Voice coil actuators in hard drives reposition in milliseconds, with consistent accuracy every time.
Scalable across orders of magnitude: The same physics that moves a 2-gram read/write head also moves a multi-ton wind turbine rotor. It's the same principle, just more magnets and more current.
Whether something is spinning continuously, sweeping back and forth, or holding a precise position against a load, there's almost certainly a highly-engineered magnetic assembly involved somewhere in the energy chain.
QT Magnetic Solutions is an industry leader in custom rotors, linear drives, permanent magnet components, and voice coil motors (link to VCM page). If your project involves high-precision motion control and you're trying to figure out what kind of magnetic assembly fits, contact us! (I'll be over here looking at every motor and speaker I own with new eyes. Everything is magnets. Everything was always magnets.)