Amazing Mystery Motor

L

AY it down, turn it over, stand it up, raise it high, turn it around, move it back, push it forward—but the Amazing Mystery Motor keeps on going. Astounding? It sure is. Especially when you consider the way most other motors work. Get their armatures the slightest bit out of whack and everything stops. They just sit there and growl. Not so with the mystery motor. It runs when held in virtually any position over the power coil,

Ever disassemble your electric drill’s motor? You end up with a pile of washers, bolts, screws, bearings, brushes, springs, dirt and oil. It’s pretty complicated. A motor need not be, though. The mystery motor has only five parts! With less effort than it takes to replace the brushes in a hand drill’s motor you’ll have a mystery motor spinning up a real breeze. Want your own? Wind the mystery

MOTOR’S coil (left) is wound on plastic film reel. Solder AC cord to wires and cover with tape. Insert soft-iron ring with a slit cut in it (below) in the hub.

ABMATURE ring (below) is plastic. Be sure to drill hole for shaft through center of piece of magnetic strip to prevent vibration.

FINISHED and ready to spin (above). Install coil in soft-iron cover and use rubber grommet to protect AC cord. Armature in holder is at right. Be sure it spins freely and does not rub against ring. Use a longer shaft if armature is to drive a cardboard fan blade. motor’s power coil on a plastic form, such as a 100-ft., 16mm movie film reel. The coil is 3,600 feet of No. 38 enameled wire. Inside the hub insert a ring of soft iron. Cut a slit in the ring as shown. After winding the coil, remove the enamel insulation from the wires and solder an AC cord to them. Then put the coil in a soft-iron case, leaving the top open. The armature’s plastic ring is 3/8 in. thick and has an inside diameter of 11/4

in. The l 3/16-in.-long armature is made from a piece of flexible magnetic strip, available from Lafayette Radio Corp., Ill Jericho Turnpike, Syosset, N.Y., 11791. The price for a minimum length of 3 ft. is $1.69 plus postage. The stock No. is 14 C 3307K. Drill a l/16-in.-dia. hole through the long axis for the shaft. Then drill holes in the ring and slip a piece of wire through the ring and armature. Lubricate the shaft.

BEST POSITION FOR SELF STARTING

S

MAGNETIC STRIP

N

A

A AXIS OF ROTATION

TOP OF COIL POS 7

POS 1 POS 3

POS 5

POS 6

POS 2

POS 4

N

+

S + N

S

S

+

N

S N SOFT IRON COVER

S

+

+

N

N

S

S

N+ S

N

+

S N

MAGNETIC FIELD COIL WINDING

SECTION A-A

SOFT-IRON POLE

117 VAC.

NOTE in sketch in upper left comer (hot N and S poles are on sides of magnetic strip. Profile diagram shows how armature turns to provide position of equilibrium to lines of force. At bottom, as armature starts to turn to line axis up with lines of force, the momentum keeps the armature turning.

DIRECTION OF ROTATION TO EQUILIBRIUM POSITION MAGNETIC FIELD

N

+

AXIS OF ROTATION (PERPENDICULAR TO PAGE)

S

COIL COVER

Plug in the coil. Hold the ring near the coil’s edge with the armature’s axis parallel with the coil’s top. If the armature doesn’t turn, start it manually. How does it work? In mysterious ways, for sure. Take a look at the lower half of the top diagram which shows the magnetic field above the motor’s coil. Note that the lines of force (for the moment we’ll assume they’re produced by DC) con- centrate around the edges of the coil. Put a piece of magnetized iron in this field and it will turn so its N-S axis is in the same direction as the lines of force. It turns to establish equilibrium with the coil’s lines of force. Consider the armature and coil shown in the bottom sketch. When the armature is oriented as shown, every time the field reverses, a pole (arbitrarily, S, here) of the armature tries to turn to follow. You might think that the armature would move back and forth in step with the AC field reversals. It doesn’t because the S pole tends to move to an area of greater magnetic flux density. Therefore, it moves counterclockwise toward the coil’s edge and assumes an equilibrium position. What you have just seen is the armature turning to provide a position of equilibrium for the coil’s lines of force as the armature is moved across the top of the coil to Pos. 7. To get the armature to turn, we feed AC to the coil. Now the mystery motor’s armature is not just an ordinary piece of iron. It has a strong magnetic field of its own. Feeding AC to the coil causes the coil poles to change from N to S. If the armature is free to spin and is started manually it will try to lock onto the rapidly-changing field and turn in synchronism with the AC frequency. Plug the coil into an AC outlet and place the armature in Pos. 1 as shown in our drawing. Try to turn the armature away from the position it first assumes. Note that it tends to lock itself in this position. When turned too far it snaps 180° to the next position. Now move the armature across the coil face as shown and notice how it turns. Why does it keep spinning? Because the armature has mass and, therefore, inertia and it continues spinning once started. When turning to a new position (or with some help from your fingers), the armature picks up enough speed and momentum to keep it going. It then continues to turn in step with the alternating field. The things which cause spontaneous starting are vibrations and normal armature unbalance. By the way, Pos, 3 is best for self-starting.— Vemon J. David *