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?
Demonstrations You Can Give
Make a display board showing the parts of the toy motor and explain how each part works compared with the parts of a commercial motor.
For Further Information
There are several other types of toy motors you can build. Your club leader or power supplier can help you find information about them.