I have a question about DC motors?

Question

I'm doing a project in my physics class where we have to build a DC motor powered by one AA Battery.

Mine didn't work, and I need to find the answers to these questions.

-What happens to the direction of the motor's spin when the battery is placed in the opposite direction?
-What will happen to the direction of the spin of the motor if the commutator is rotated 180 degrees?
-What will happen if the commutator is placed in the same plane as the armature?
-What happens if you connect 2 batteries to the motor? 3 batteries? A 6V battery?
-How would you redesign the motor so it could run on 15 Volts?

Answer 1

Assuming you have a constant magnetic field - in both polarity and strength - on the stator (either by permanent magnet or by electromagnet), you'll get:

1. Changing the battery polarity (i.e. armature field polarity) will reverse the rotation.

2. If the commutator is rotated 180 degrees, the most likely occurrence would be a flashover condition - no rotation. The polairty of the brush arms is dependent on the polarity of the stationary magnetic field.

3. Not quite sure what you mean by the same plane ... the commutator is in the same horizontal and vertical plane (when the motor is mounted horizontally) as the armature. It is only axially that there is a difference. If you were to move the commutator inside the armature (making it axially co-planar as well), then you'd have to figure out how to get the brushes to make contact.

4. For the same stationary field strength, adding more voltage to the armature side will speed up the machine. Twice the voltage will be (approximately) twice the speed. Eventually you won't be able to commutate successfully (brushes jumping due to peripheral speed issues).

5. How to operate on a different voltage (i.e. 15 volts instead of 1.5) ... depends on what the constraints are. In the simplest case, just apply the higher voltage and live with the higher speed. Alternatively, increase the stationary field strength to effectively "slow down" the machine when operating at the higher voltage.

Answer 2

1. If you reverse polarity, the motor will spin in the opposite direction.
2. The direction of spin will remain the same.
3. ???
4, An increase in voltage, provided that the windings insullation is suitable will produce an increase in speed.
5. Make sure it's properly insullated. The design should be the same.

Answer 3

Sorry, it doesn't really sound like you've done your homework.