Electric Motors 5/12/2014

We began class with modeling of pins.  We found out that iron can be magnetized and we took ordinary iron paper clips/pins and rubbed it along a magnet.  Before magnetized, the magnetic domain elements is scattered and as we magnetized it, the domain becomes aligned, turning paper clips into a magnet.

Non-Magnetized (left top) v.s Magnetized paper clip (left bottom)

Next we tried to dis-align these domain elements in the iron by smashing, burning, to vibrate the molecules out of place.  the semi-disordered iron does turn out to be less magnetic.

We then refreshed our memory by calculating the net force on a looped current-running wire.  We use the right hand rule:  Simple and we discovered torque depends on the rotating axis F = ILB

When torque is involved, that's when rotation begins.

Based on our model, the coiled square-shaped wire torque turns halfway, and becomes 0, then eventually a negative torque rotates it the other direction.  As a result, it wiggle-wiggle-wiggle-wiggle-wiggles.......

All these torque talk is to introduce the electric motor (basically a wire inside)  The simplest two-pole DC motor consists of a coil, two pieces or magnets, a commutator, and a power source.  As found by torque, the electric current carrying wire tends to wiggle back and forth unable to finish a full rotation.  Two ways to fix this:  1) flip the magnets 2) reverse the current.  Since #2 is much easier, this is what the commutator is for.

As the two contacts is aligned, it shorts out the battery leaving the coil to coast over the "hump".  It runs in a push-coast push-coast push-coast push-coast fashion.

 Push (Left).  Coast (Right)

Next, perhaps the more unforgettable experience of this semester we get to make our own motor!!!
applied about 3 Volts

To demonstrate how motor works, we hooked up a sample motor simply by connecting a power supply to the two terminals outside the motor.  WARNING NO MORE THAN 3 VOLTS!

Motor (coiled shaft) began turning as soon as a current runs through the wire.  

When we reversed the current, the motor started rotating the opposite direction.  When we turned the power supply up, the motor speeds up.  Therefore, the speed depends on the voltage supplied.  Alejandro putting the motor on OVERDRIVE cranking as high as 5 VOLTS!!  we started seeing sparks and smelling the commutator brushes getting cooked!

Cranking things UP a notch!

building from scratch, we get an anamo-coated wire, two paper clips to hang the wire on, and a cup for the platform of the magnets.

We used sandpaper to sand off half of the anamo insulating surface on one side of the wire contacting the paper clips so it acts as the commutator.

Stephanie's group's self-running motor!

Dez's group's double motor configuration!  WINNER!

David's group's biggest coil, smallest  magnet motor!

Last, Prof Mason set up a pole and placed a bunch of compasses surrounding it.  All the compasses were originally pointing North.  As soon as the power supply was turned on with current running the wire, the compasses started pointing in a circle around it.

 By our observation, we conclude the magnetic field is going in a circle.  As we moved the compasses further from the pole, the effect becomes weaker.  This tells us that the magnetic field is proportional to distance.

When we reversed the current, the compasses reversed, turning the opposite direction.

 We use our right hand again and point our thumb in direction of the current and our fingers would curl the direction of magnetic field.

Last, we experimented if the magnetic fields superimpose.  Prof Mason set up a wire running parallel adjacent to each other in both same and opposite direction:

We found out when the wires ran in the same direction (Location #2), the  magnetic fields doubles and when they ran opposite direction (Location #3), they cancel out.