Why doesn't the domestic DC engine work?

Because the current direction of DC motor is unchanged, the magnetic field force will be opposite to the motion direction when rotating to the equilibrium position, so that the motor can not rotate all the time.

In fact, the main reason why the motor can keep rotating is that there is a structure called commutator, whose function is to automatically change the direction of current in the coil every time the coil turns to the equilibrium position, so as to ensure that the direction of magnetic field force on the wires near the N pole and the S pole remains unchanged and keep the coil rotating in the same direction.

Because the commutator of self-made motor is difficult to make, the purpose of scraping off half is to make the coil turn to the lower half without current and magnetic force (at this time, magnetic force is resistance). The coil can rotate to its original position due to inertia, and then the current is subjected to magnetic force (in this case, power), so that the coil continues to rotate.

As mentioned above, the coil will not rotate all the time, because the magnetic force in the lower half is resistance, which prevents the coil from continuing to rotate.

Extended data:

Rated value of DC motor

1, rated power PN: mechanical power output on the motor shaft.

2. rated voltage UN? : DC voltage applied to armature under rated working conditions. (for example: 1 10V, 220V, 440V)

3. Rated current IN? : Current when rated power is output on the shaft under rated voltage (shunt excitation includes excitation and armature current).

4. The speed of 4.DC motor is generally above 500 rpm. The speed of the dedicated DC motor can be very low (for example, several revolutions per minute) or very high (more than 3000 revolutions per minute).

References:

Baidu encyclopedia -DC automobile

References:

Baidu encyclopedia-electronic commutator