eli5 how small motors and rotating things work? Where does the rotating start?

Question

Take something like a drill.

I understand its electric, I understand that in some way the electricity makes sothing move and then that movement is turned into spinning through gears and engineering magic.

But where does the initial movement come from? All i can picture is something is spinning or rotating because something else is rotating. But it has to start somewhere right?

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Answer 1

For the motors in many small tools and toys, you have a set of permanent magnets, and a set of electromagnets. One set is mounted on the shaft (the “rotor”) and the other on the stationary bit (the “stator”). The electromagnets are “soft” iron, wrapped with coils of copper wire. The electromagnet “becomes” a magnet when a current flows through the wire; the stronger the current, the stronger the magnet (up to a point).

(NB “Soft iron” = alloys and preparations of iron which will stick to a magnet, but will not become a permanent magnet themselves)

Crucially also, the *polarit*y of the electromagnet (which “end” is the north or south pole) depends on the *polarity* of the current.

To make a motor *keep going*, rather than just jump a bit when power is applied, you need to periodically reverse the polarity of the electromagnets as the motor rotates, so the electromagnets keep pulling (and pushing) the rotor by attraction/replusion to the permanent magnets.

Until 20-odd years ago, most common small motors used stationary permanent magnets on the stator (the outside, stationary bit), and electromagnets on the rotor shaft. A “split commutator” was used to connect the power to the rotor, this cleverly switched the polarity to the electromagnet coils as the rotor rotates.

Modern high specification motors use electronics to control and switch the current to the electromagnets, and can also vary the exact strength of the electromagnet with time (and angle of the shaft). This allows precise speed and torque control, and in particular allows for precise constant torque – which means that even really big motors can run super-smoothly and silently with practically no hum or vibrations. They can also be more efficient, which means they can deliver more power, be smaller, and run cooler.

(I cant really believe that every kid didn’t take their Hornby trains to pieces and have a look at the innards of the motors… (and put a drop of oil on them) Not everyone had engineering parents, I guess)