Step No. 4—Armature Supports and Brushes
Scrape the insulation from the ends of two 6" pieces of wire. Tack them to the base and bend them as shown to make brushes.
Drive two pairs of 3" brads into the base about 3-1/4" apart and in a line midway between the field poles. Wrap wire around the supports to form armature bearings.
Scrape insulation off ends of wire from the field. Connect one end to a brush wire.
Assemble As Shown
Adjust the position of commutator and tension of brushes against it for best operation.
Take the armature off the motor and connect the commutator wires to a dry cell battery. Test the polarity of each end of the armature with a compass. Switch the connections on the commutator and test again. See how the compass needle changes direction?
With the armature still off, connect the field coil directly to the dry cell. Test the polarity of each end of the field with the compass. How can you reverse the polarity? Try it. It's easy.
Reassemble the motor again and start it. Push the field poles slightly out of alignment with the turning armature. What happens to the motor's speed? Can you tell why?
This time, push the field poles completely out of the way. Test the polarity of the armature as you slowly turn it by hand. Do you see what happens and why it does?
Try to reverse the direction of rotation of your motor by reversing the connections at the battery. What happens? Can you explain why?