Szechenyi Istvan
Grammar School

H-2400 Dunaujvaros,
Dozsa Gy. ut 15/A.
Hungary
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Magic motors

Construct a DC motor without a commutator, using a battery, a permanent magnet, and a coil.
This was one of the exercises of the International Young Physicists Tournament in 1999.
We solved the problem in practise in two different ways, so we built two devices. The device in the second solution is so easy to build that we can even do it at home without any special equipment, and we can really feel success, when it starts to work.

I. Rotating soft iron cylinder

We made an endless close wound coil onto a rotary -around it's symmetry axis-, soft iron cylinder-skirt (we brazed together the front and the end of the coil). The covered wire made of copper that forms the winds of the coil is in the direction of the barrel cam. (See the picture.)

Than we filed the wires at one place on the outside of the cylinder in order to free it from its cover at that places. Two contact blocks provided the current here (at the opposite sides of the cylinder).
A force acts to the wires on the outside of the cylinder, because of the current streaming in different directions in the half-coils; and the magnetic field of the permanent magnet. The torque of this force points to the same directions in both half-coils.
It's important, that the cylinder is made of soft iron, because this (with its magnetic shielding) precludes the magnetic field of taking effect on the wires in the cylinder, in which there's current. This is important, because the direction of the force acting onto the wires on the outside, and inside would be opposite, so the sum torque would be zero.

motors.m1v

(4.8 MB)

II. A motor made of wire

We constructed a rotary coil of covered wire so that the two ends are the axles of it. Afterwards we filed these ends acting as axle semicircular. (See the picture.)
This is almost unnoticeable at a thin wire that's colour is like copper. We placed this coil on a U-shaped wire on the two contact blocks of a battery, we also fixed a permanent magnet on the battery. After starting to rotate the coil, it keeps rotating, because it gets current only in the half period of the rotation, when the torque of the permanent magnet's magnetic field helps the rotation. At the other period, only the existing rotation helps the coil to rotate.

motors.m1v

(4.8 MB)