Motor

      

There are two motor projects here.  If you are feeling ambitious, this first motor is fairly easy to build and has impressive power.  If this is your first motor project, you might want to try the simple motor first.  It is super easy and will amaze your friends.  Either of these motors would make a great science fair project.



Gallery

Here are other people's builds of this motor.  Nice Work!



Anja Bea was able to power her motor with only a 9-volt battery, by standing the rotor vertically and using a piece of glass as a near friction-less bearing. Excellent Build, Anja Bea!!!

Mantis Toboggan did a great job upgrading his commutator to solid copper plates.  They are a little more work, but they give you better contact, and longer life.  Awesome motor build, Mantis!


Farah Fahmi had a hard time building this motor, but he did not give up.  After 2 stators, 3 different types of wire, and four rotor windings, Farah got this motor running on New Year's Eve.  I personally could not think of a more exciting start to 2015 :-)  Good job, Farah, and great show of will power!


Questions/Tips:

How does a motor work?

The stator has a North and a South magnet. The rotor has a North arm and a South arm. It flips over to get its North arm next to the South stator magnet and its South arm next to the North stator magnet. When it gets there, however, the commutator flips the direction of the current flow through the rotor, which also flips the North and South Arms of the rotor, and the process starts over again. Its is kind of like like a dog chasing its tail, and never catching it

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How does the little motor work without a commutator?

Excellent question! The rotor jumps up and breaks electrical connection, during part of each revolution. The rotor is arced slightly, so that, unpowered, it naturally rests with the N pole downward. If the permanent magnet’s N pole is facing up, as soon as you power the rotor, it: 1-flips over, 2-lifts up and breaks the connection. Without power, it keeps rotating around to its original N-pole-down position, and sits back on the stator, to get more power to do the whole thing again. -Lou

         

Where did you get the wire?

I don't remember where I got the wire, but just google 22 AWG solid copper insulated wire.  It should look like the picture above.  The insulation should be clear, like enamel, so you can see the copper color.  You can get a 1/4 pound roll on Amazon for about $10 or a 1 pound roll for $20.  You only need a 1/4 pound for this motor.

How did you wire the battery pack?

I took approximately 2-inch long pieces of house electrical wiring, bent hooks on both ends, and hooked them between the plus and minus spring terminals on each of the batteries, so that they were wired in series. I put all the batteries together in a box so they wouldn't move with the pressure of the tugging wires. You could achieve the same thing, simply by wrapping them all together with duct tape.  Here is a picture of mine.  Click on it for a larger view.



Can I use 3 9-volt batteries, instead of 4 6-volt ones?

No, Sorry.  Even though three 9-volt batteries have more voltage (pressure), the four 6-volt batteries provide a lot more amperage (flow).  You need that big flow of electrons running around the coil, to produce a strong magnet.  Power = Voltage x Amperage.  The little 9v batteries barely trickle amperage, so the power ends up pretty low. Think soda straw versus garden hose :-)


Why does my pipe fall through my PVC cross?

Some PVC crosses are looser than others. To fix, you can wrap some tape around the metal pipe, before you shove it in. You can also glue it in place, or drill a hole through the cross and the pipe and put a cotter pin, machine screw or nail with bent end to hold it in place.
 
 
Why doesn't my motor work?
 

If you built the motor, but it is not working, don't give up.  Here are some things to check:

 

Tape

Make sure you have tape on both of the commutators.  With the rotor arms pointed out sideways at the magnets, look directly down on the motor.  One of the commutators should appear completely covered with tape, and the other should appear completely bare.  Flip the rotor over, half a turn, and the taped/bare look should flip too.

 

Magnets

Make sure your magnets are facing the same way. That is, both North poles should be either facing right of left, not one each way.

 

Caps

Spin the rotor and look at your plastic end caps.  If the nails are not exactly in the center, you will see a wobble in the caps.  This wobble can cause the commutator to pull away from the brushes, and lose power.  If a cap has a bad wobble, replace it with a new cap, with a very carefully drilled center hole.

 

Power

With the rotor out of the motor, make sure you are getting 24 volts across both sets of brushes.  If not, check all your wiring.  Measure across each battery, and then two, three, and four at a time.  Each battery should add 6 volts to the total, up to 24.  If you don't have a voltmeter, you can usually get a cheap one for $10 at the hardware store.  Amazon.com has them for as little as $6. 

 

Rotor

With the rotor out of the motor, make sure the rotor reads zero ohms of resistance from one commutator to the other.  If not, and you used more that one peice of wire on the rotor, make sure the enamel is scraped off the end of the wires, where you twist them together, so you get a good connection.  Also, don't forget, you need to sand all the enamel off the commutators, before you apply the tape.  If you don't have a voltmeter, you can usually get a cheap one for $10 at the hardware store.  Amazon.com has them for as little as $6. 

 

Brushes

The perfect tightness of the brushes, against the commutators is crucial.  If they are too tight, the rotor won't spin.  If they are too loose, the rotor will not get the electricity it needs.  The best way to adjust this is to bend the copper loops so that none of the brushes touch the commutators.  Next, with the thumb and forefinger of your left hand on the loops of one commutator, and the thumb and forefinger of your right hand on the loops of the other commutator, gently press the loops in, until they just touch.  Have someone spin the rotor by hand, to get it started.  Work to find just the right pressure to keep the rotor going and a good speed.  Once you find the right pressure, bend your copper loops, so that they apply that same amount of pressure.  This adjustment can be tricky.


Why does my rotor "stick" to the stator magnets?

Some people find that their motor will not spin, because the metal pipe, in the rotor, it is attracted to the magnets on the stator.  That is normal.  If you spin the rotor of any toy motor, by hand, it will feel bumpy.  That is the rotor being attracted to the magnets.

But, it is not normal if your motor is not turning :)  The basic problem is that your magnets are stronger than your electromagnets(rotor windings). The magnets are so strong, that they hold the rotor in place, fighting the urge of the electromagnets to spin it.  There are three solutions:  

1 - Reduce the strength of the magnets by backing them away from the rotor, or replacing them with weaker magnets.  Try this as a potential quick fix.
2 - Replace electromagnet's core (the metal pipe) with a plastic pipe.  This will totally eliminate the pull of the magnets on the rotor, so the "problem" will be gone.  However, this reduces the focus of the electromagnets, so they end up not as strong.  Do this, if this is a school project you need to get working ASAP.
3 - Increase the strength of the electromagnets, by increasing the number of windings on the rotor and/or increasing the voltage.  This option will make the most powerful motor.  Do this if you want a motor that will impress your parents and friends.



How do I make it spin faster?


If you have done everything above, and you still want more speed, try these tips:

1 - Increase the voltage by adding another battery.  

2 - Put more windings on the rotor arms to make stronger electromagnets.  

3 - Replace the simple metal tabs that hold the rotor with little ball bearings, to reduce friction.  

4 - Hammer your brush wires flat into more of a copper ribbon to get more contact with the commutator.



How do I add windings to the rotor arms?


Adding windings is possible, and not too hard.  The hardest part is splicing them into the existing wiring.  You  have to cut the single wire that goes from one rotor arm to the other, splice and wrap more wire on each side, and then splice them back together.  To splice, simply sand about an inch of enamel off each wire and twist them together.  You should not need to protect these new connections, since they will not be in contact with any other conducting surface, but you can put tape over them if you want.



Can I make it lift a weight?


Yes, This motor, will lift a small weight (1 pound or less ) by winding a string around one of the nails.  However, you can use pulleys and a belt to reduce the speed and increase the torque (lifting power).  Google "FingerTech" or "PowerGrip" pulleys and belts.  Put a small pulley on the nail motor shaft, and a large pulley on another shaft that will wing up string and lift your weight.  Use at least a 4 to 1 ratio in pulleys to give you a 4 to 1 increase in torque.



The Math


The main equation we need to consider is B=unI.  B is the strength of the magnetic field, in the rotor, which we want as high as possible.  The equation says we can influence that with three factors: u, n, and I. u (actually the Greek letter mu) is the magnetic constant.  We increase that significantly by making our rotor arms have a steel core, which has a higher mu than a plastic core.  n is the coil density, and we increase that by winding as much wire as we can on the rotor arms.  I is the current which we increase by having a high voltage (24 volts) and by having large (lantern) batteries that can supply lots of current.  The size of the wire we need is determined by the equation P=VI, where P is the power rating of the wire, V is the voltage, and I is the current.  Google 'solenoid equation' for more info.

I did not use these equations, specifically.  I just knew I needed lots of windings, voltage, and a metal core.  I also bought "magnet wire" which is what is typically used for making electromagnets.  If certainly is possible to apply math to a motor, but there are many other factors to consider.  Friction of the rotor against the bearings and commutator, for example, are probably more significant than anything listed above.



Why use PVC?


I used PVC in this motor design, for several reasons.  A motor must have rotor arms perpendicular to the axis of rotation, and a PVC cross is an ideal part to accomplish this.  PVC piping is also much easier to cut and drill than metal piping, and can simply be pressed together, rather than soldered.  PVC is strong enough for this application, yet light, so it reduces friction on the bearings (nails).  Lastly, PVC is a non-conductive material.  If everything is wired correctly, this should not matter, but PVC is more forgiving if you accidentally have a bare wire touching the commutator.


Parts List


1/2" PVC pipe, 6 inches 1/2" PVC Cross 1/2" PVC Caps, 2 of them 3/8" x 4" threaded metal pipe 2 magnets 4 angle brackets, 1.5 in x 1.5 in Stiff copper wiring, 14 gauge or thicker 22 gauge enameled magnet wire, 1/2 pound spool or more Four 6-volt Batteries Wood 2" x 2" by about 3 feet long. Two nails, about 3 inches long. One plastic straw, Electrical Tape, Various Screws

Tools 

A drill with various bits
Pliers
Wire Cutters
Screw Drivers
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