ELECTRIC MOTOR

OBJECTIVE:

To learn how an electric motor runs and the parts of a motor through the construction of a DC motor.

SKILLS LEARNED:

Open and closed circuits Understanding of the basics of the electric motor and the direction of electron flow

TIME:                       Two to three hours.

INSTRUCTOR NEEDS:

One volunteer per five 4-Hers.

PARTS LIST:

Electric Motor Kit
Coil of copper magnet wire
9-volt battery
Battery clip (optional)
(Parts available from electronics hobby stores)

COST:                      Motor kit - $ 3.00
                                Battery - $1.50

TOOLS & SUPPLIES:

Fine sandpaper
Transparent tape
Pocketknife
Needle-nosed pliers
Yardstick

ASSEMBLY PROCEDURES:

A. BEFORE YOU BEGIN

1. Read and understand all instructions.
   
   
2. Remove all parts and check. Return small parts to envelope.
   
   
3. Unwind coil of wire, taking care not to kink wire.
   
   

B. WINDING AND INSTALLING THE FIELD

1. Place field pole and base plate together and join with a short piece (1") of tape.
   
   
2. Cut wire, 32". Remove 1" of insulation from both ends of wire. (To remove insulation from wire, pull section of wire to be cleaned through a folded piece of fine sandpaper several times. Thorough removal of insulation is essential for good motor operation.)
   
   
3. Allowing 5"-6" for a battery lead, begin at one end of base and wind evenly and tightly, 23-24 turns. A short length of wire should remain (2 to 21/2").
   
   
4. Fasten field to cardboard with prongs, with battery lead secured under one prong.
   
   

C. WINDING THE ARMATURE

1. Place armature halves together and join with short piece of tape.
   
   
2. Push shaft between plates.
   
   
3. Cut wire, 21". Fold in half and place over armature at the shaft with the bend toward long end of shaft. Loop wire around shaft as shown. Winding of wire should result in one continuous winding from one end of armature to the other, with all windings in the same direction. When winding is finished, wire ends should be toward long end of shaft with each end approximately 11/4" long.
   
   
4. Count windings to be sure there are the same number (8 to 10) on each side of the shaft.
   
   
5. Remove 1" of insulation from ends of wire to within approximately 1/2" from armature.
   
   
6. Adjust shaft so short end is approximately 1/2" long.
   
   

D. MAKING THE COMMUTATOR

1. Cut 3/8" piece of tube and slide it on long end of shaft up to armature.
   
   
2. Slide one disk on shaft with small holes toward flat side of the armature.
   
   
3. Cut another 3/8" piece of tube and slide on shaft.
   
   
4. Slide second disk on shaft as in step B above.
   
   
5. Wires from armature are inserted through small holes in disks. Check to ensure all wire between disks has been cleaned of insulation. With disks and tube pieces snug against armature, bend ends of wire outward to 90 degrees from shaft. Clip extra length, leaving 1/4". NOTE: It may be easier to insert wires through the holes as the disks are being put on the shaft.
   
   

E. INSTALL ROTOR (ARMATURE AND COMMUTATOR ON SHAFT)

• Cut one piece of tube 1/8" for short end of shaft. Cut one piece of tube 3/8" for long end of shaft.
  
  
• Install one support, then rotor, then second support, fastening to cardboard with prongs.
  
  
• Adjust supports (or cut tube) as necessary to allow a close but not too snug fit.
  
  
• Check rotation of armature in field to ensure rotation without hitting. Carefully spread field poles as necessary.
  
  

F. INSTALL BRUSHES

1. To make the first brush, fasten the short wire from the field to the cardboard with two prongs, heads up, using outer hole first. Bend wire 90 degrees from cardboard up to commutator. Be sure the section of wire in contact with the commutator has insulation completely removed.
   
   
2. Remaining wire (7") is used for second brush and battery wire. Remove 1" of insulation from both ends. At one end, bend a 11/4" section of wire at 90 degrees to make the brush. With the brush at the commutator, use prongs to fasten wire the cardboard, with prongs up. Loop wire around head of outer prong to secure. Again be sure wire in contact with commutator has insulation removed.
   
   

G. RUN MOTOR

1. If used, connect battery clip to ends of wire leads from motor.
   
   
2. Connect battery to battery clip. Give rotor a spin. Try both directions.
   
   

H. TROUBLESHOOTING IF MOTOR DOES NOT RUN

1. Check all contact points to insure removal of insulation and corrosion.
   
   
2. Be sure brushes are in contact with both commutator wires at the same time. It may be necessary to adjust the position of the brushes slightly by bending them.
   
   
3. Commutator wire between disks should be straight, and parallel with the shaft.
   
   
4. Rotate commutator slightly on shaft to adjust for best running.
   
   

BASIC ELECTRICAL CONCEPTS:

Converting electrical energy to mechanical energy is accomplished through the use of an electric motor. In the motor we built, the electrical energy stored in the battery is used to create magnetic fields that cause the rotor to turn.

Magnets consist of two poles, north and south, that are the opposite ends of the magnet. If two magnets are placed close to each other, like poles tend to repel one another, and unlike poles attract. A special type of magnet, called an electromagnet, can be created from the electrical current flowing through a wire. This is accomplished by winding turns of wire around an iron core, and connecting the wire across a voltage source, such as a battery. The poles of the electromagnet can be changed by reversing the direction of current flow through the wire.

Our motor consists of two electromagnets, the stator and the rotor. The poles of the stator remain constant when we apply voltage, while the poles of the rotor reverse as it spins. Remember that the commutator is simply the ends of our coil on the rotor. As it turns, making contact with first one brush and then the other, the direction of current flow reverses, changing the poles of the rotor. This causes the rotor poles to alternately attract or repel the poles of the stator, making the rotor spin.