Creating large DC Motor for Funzies. Won't work.

  • #1
Flyingwing12
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A picture I included shows how my motor is constructed. The basic science fair project looking engine. This engine is actually designed to do work, however, it will not turn over once DC is connected to it.

The wire is close to 5/64 inch thick and the whole rotor is solidly soldered together. I had a heck of a time finding Magnets for the thing and finally found a circle magnet form a CB radio antenna. I was able to see some movement when 4 C cells were used as power, but no rotation was able to be achieved.

What have I done wrong folks? Thanks for you're help if you help me ;)
 

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Answers and Replies

  • #3
Bobbywhy
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Flyingwing12, Welcome to Physics Forums!

If your motor doesn’t rotate then there is some mistake in the construction or electric power connection (or both). You may compare yours with these to find the error:

Your drawing looks a lot like this one:
"How to build a simple electric motor":
http://www.hometrainingtools.com/build-motor-project/a/1605/

Magnet Motor Kit:
http://www.miniscience.com/projects/magnet_motor_kit/index.html\

Hundreds of photos and images of simple dc motors:
http://www.google.com/search?q=simp...gG93YDQBQ&sqi=2&ved=0CFEQsAQ&biw=1223&bih=619
 
  • #4
Flyingwing12
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I am confused because the construction of my motor is just like the smaller ones. I have jumped up the volts, and jumped up the magnet. I am just curious as to why it doesn't work.

There must be some reason?

Check out the picture on the first post.
 
  • #5
Flyingwing12
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If connected to a DC wall outlet converter the converter senses the short circuit and shuts off.

A car battery causes the wires to melt, and a 12 volt power supply does the same thing.

These devices are averaging at about 8 AMPERES. Could the Amps be ruining my experiment?
 
  • #6
I_am_learning
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Can you post a picture of your setup?
Wires melting is clearly a problem. Either use lower Voltage or huge thinner wires.
 
  • #7
I_am_learning
686
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Your design is also not good one. Using Coils would allow you to have much more torque by flowing little current. Also wire melting problem can be mitigated because, the long length of wire will reduce current flow.
See Post #3 links, by Bobbywhy.
 
  • #8
Flyingwing12
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Here is a picture of the motor. I chose this design because it shows the beauty of movement! All of the other designs are small and compact which don't interest me.

Everything on the rotor is SOLDERED together. The tape is just to protect my hands form the pointy protrusions
 

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  • #9
I_am_learning
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See the basic theory
F ~= B*N*I*L
In your case no. of turns N = 1.
Lots of design use at-least N = 15-20.
So, you need to compensated your N=1 by increasing I by 15-20 times, provided you use magnet (B) of same capacity. You seem to be using alnico magnet, which isn't as powerful as neodymium magnets.
The wires seem very sturdy, I don't think it melts with 8-10A. How long did you let it on?
The only thing you could do is increase the current even more.
But you need to make really sure that the support is friction free and the thing can rotate even with slight force.

Once again, design change is what I suggest. You could easily scale up the 'compact' design.
 
  • #10
davenn
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Here is a picture of the motor. I chose this design because it shows the beauty of movement! All of the other designs are small and compact which don't interest me.

Everything on the rotor is SOLDERED together. The tape is just to protect my hands form the pointy protrusions

a number of problems some of which I_am_learning referred to
one other is the magnet ... not what the manget if made of ... ''You seem to be using alnico magnet, which isn't as powerful as neodymium magnets.'' that I_am_learning also commented on, that's of least importance and your problems.
The big problem is the shape of the magnet and its orientation to the coil. You cannot use a single magnet in the way you have shown
Look closely at the drawing that dlgoff showed in his post above and particularly note that the coil sits BETWEEN the N and S poles of the magnet

The single turn of wire as you have will not work ... although you may think you have multiple turns, you don't they are just single strips of wire in parallel with each other.
You need an actual coil of wire with multiple turns that starts at one side of the upright and goes through to the other side/upright
You will be able to make it work that way which is a variation on that drawing that has bother end of the wire coil coming out the same side

Dave
 
  • #11
Flyingwing12
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Could I wrap the entire thing in copper wire? Make it look somewhat of a sphere?

I have a feeling that the wires are heating up because I do not have these coils of wire that you suggest. The multimeter does show low resistance...

I have made smaller models that have worked. They looked just like this. Although they had about 1-3 turns of wire.

Will try to improve it.
 
  • #12
Averagesupernova
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Flyingwing12, before we go on I would ask you if you know what a commutator does.
 
  • #13
Flyingwing12
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I know that it switched the current direction, right?

UPDATE:

Found magnetic wire in an old treadmill. Made a large 7 wind circle and got it to barely wiggle when 6vDC was applied.

I think it is my magnet...
 
  • #14
NascentOxygen
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Hi Flyingwing12. I have a lot of time for experimenters, being one myself, so it's interesting to see how you are going about the design of a model motor. You will learn a lot from this. As other have pointed out, there may be two problems: the magnet, and the rotor. :smile:

To see whether you stand any chance of getting movement. disconnect power from the rotor but leave the rotor there, no need to move it. Now, between those wooden blocks temporarily sling a single length of flexible copper wire horizontally above the magnet—this will be like a simplified rotor. How to suspend it? Hang a short length of string from a drawing pin on each block to suspend the wire so it's free to swing up/down/sideways. This moveable wire will reveal any repulsion between it and your magnet when that wire carries current. Do you have some means to limit the current, as a thin piece of wire is likely to overheat and melt. Perhaps connect a 12v car headlight globe in series, if your only power source is a car battery.

Should that single wire show no inclination to move when powered, then you are wasting your time trying to get your more elaborate "eggbeater" rotor to spin. It will be time for a rethink.

Good luck with your demonstration.

A very simple motor: http://m.youtube.com/#/watch?v=IQS1ZE0TVeo
 
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  • #15
Averagesupernova
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I know that it switched the current direction, right?

So does your motor have one? And if not why do you expect it to work?
 
  • #16
Flyingwing12
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I proved today that a single wind of magnetic wire works. I was able to make a small 3 inch diameter circle out of mag. wire and make it rotate with 9v and the same support setup as the larger motor .

The culprit in my experiment is my magnet. I notice that speaker magnets don't have a wide spread field like this little doughnut magnet I have.

Tried hooking up the "eggbeater" to a 12v supply and it melted the wires. With magnetic wire I notice that it is non conductive with the coating on it, so sanding it made the smaller rotor possible to rotate. It did not rotate on its own, I had to get it started.

Is there a formula I can use to determine the strength of a magnet that I need to get this " Eggbeater" to work.

I know it is possible. It has to be.
 
  • #17
Flyingwing12
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When you think of series are you thinking of this?

It seems as if the lamp is acting like a resistor?

I thought there is a V drop between resistors and base Voltage?

Thanks for taking interest :)
 

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  • #18
NascentOxygen
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When you think of series are you thinking of this?

It seems as if the lamp is acting like a resistor?
Yes, the lamp is a convenient resistor. :smile: I suggested that you use it so it limits the current through the strand of thin wire. If you just connect a piece of wire across a car battery there will be a big spark, the wire will glow red hot and melt, thus ending the experiment. :frown: But with the lamp in series, the lamp will limit the current to a safer level. The wire may still get hot and start smoking, but the experiment will have served its purpose: do you see instant movement in that strand of wire or not?

You must take the eggbeater out of the circuit for this single wire test so it doesn't steal the current from the piece of wire. Use a strand of wire that is flexible and hang it so it is free to move a bit, so that you can watch for movement. Because if you observe that the single strand does not move, then sure as anything neither will your eggbeater rotor!
 
  • #19
Averagesupernova
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You really need a commutator. Suppose with a single loop of wire the current is split evenly through the upper and lower loop. In order for the rotor to turn the upper wire has to move in the opposite direction of the lower wire. One wire will fight the other. Remember the right hand rule when it comes to magnetism and current flow? The reason your single loop worked at all is because the field was small enough on the top compared to the bottom so the lower 'outpulled' the upper.
 
  • #20
NascentOxygen
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I proved today that a single wind of magnetic wire works. I was able to make a small 3 inch diameter circle out of mag. wire and make it rotate with 9v and the same support setup as the larger motor .
I think you mean "it rotated a few degrees then stopped" don't you? It surely didn't keep turning and turning endlessly?
Tried hooking up the "eggbeater" to a 12v supply and it melted the wires.
So it melted the plastic-coated wires from the battery, or did it melt the egg-beater wires? (They look so thick that I'm surprised the 12v supply survived. Your eggbeater is no different from a short circuit.)
Is there a formula I can use to determine the strength of a magnet that I need to get this " Eggbeater" to work.

I know it is possible. It has to be.
Even if it is theoretically possible to get your homemade rotor to operate, it will first have to be modified a bit to give it commutator action. But I'm not suggesting you do that until we establish whether it stands any chance of working.
 
  • #21
Flyingwing12
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I got the small single wound job to spin continuously yes.

It has to be possible for this thing to spin.

I think I just need a very strong magnet.

And how would this commutator work? This keeps being mentioned and yet no one says how I should hook it up?

try using MS paint to make a diagram or something like that. They help out a lot.
 
  • #22
Flyingwing12
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And electric motors of this scale are basically short circuits right?

I thought the huge coils of non conductive wire are for resistance?

Please elaborate.
 
  • #23
NascentOxygen
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And electric motors of this scale are basically short circuits right?
Well, "short circuit" is a relative term. To a 12v car battery, your eggbeater with its heavy gauge copper wire is getting close to a short circuit. Connected directly to the battery terminals I'd expect the wires to glow red hot and melt, that is, if the battery didn't explode under the strain.
I thought the huge coils of non conductive wire are for resistance?
It's called "insulated copper wire" because the outside is covered with an insulating layer, either enamel varnish, or coloured plastic. :smile: Motors use lots of coils to produce strong magnetic fields.
 
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  • #24
NascentOxygen
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I got the small single wound job to spin continuously yes.
Great! Then why not settle for that as your demo motor? It's so unusual that most people will be mystified to see it spinning, telling you it can't be happening—it won't spin without a commutator. :tongue:

If you go to youtube.com and search for "simple motor" you will see plenty of DIY motors. You might get ideas from there. But I really think you should stay with the simple one that spins once you have got it going!

I once salvaged the electric motor from the windshield wiper assembly I found in an old car dump on the edge of a wood. The assembly was mounted at the top of the windshield, and the armature of the rotor projected through the case (as a brass rod) so it was within reach of the driver. You see, the motor was a design that isn't always self-starting, so it was sometimes necessary to twirl that rod to get the wiper's motor to start spinning!
 
  • #25
dlgoff
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It's so unusual that most people will be mystified to see it spinning, telling you it can't be happening—it won't spin without a commutator. :tongue:

edit: removed emoticon link

Anyway,

https://www.youtube.com/watch?v=Ue6S8L4On-Y
 
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  • #26
I_am_learning
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dlgoff, I don't think Commuter is needed for a half-turn configuration in a non-uniform Magnetic field. (The OP's setup.)
The videos and documents you are discussing refers to a regular DC motor with uniform fields and integral no. of turns, which surely does need commutator.
 
  • #27
I_am_learning
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To prove my concept, I tried to do this quick and dirty experiment, but it failed.

small.jpg

My guess was,
While the wire is in lower half of its imaginary rotation-circle, the torque will be produced in one direction and when it is in top half, torque will be in opposite direction.
But since the average Magnetic field strength on top half is lower than in bottom half, during each complete rotation torque should be +ve and hence, the rotation should have continued indefinitely.

I think, the inertia (due to torque in bottom half) isn't being able to overcome -ve torque + friction during the top half. i.e. I think the reason for failure is mechanical problems.

If I have some serious theory flaw, please let me know.

P.S: I do believe that coil design with commutator would surely give the best result (an order of magnitude more torque), but I am just trying to verify if other method could work* or not.
*Although for demonstration purpose only
 
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  • #28
dlgoff
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dlgoff, I don't think Commuter is needed for a half-turn configuration in a non-uniform Magnetic field. (The OP's setup.)
The videos and documents you are discussing refers to a regular DC motor with uniform fields and integral no. of turns, which surely does need commutator.
You are correct however giving the OP a little more info about motors could help his/her learning.
 
  • #29
Flyingwing12
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I had a car battery charger hooked to the motor and was only getting 9 volts out of it. This was until I moved the motor and it made contact, in which the wires were instantly fried!

What caused the voltage to be 9 volts across the pos/neg wires?
 
  • #30
NascentOxygen
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I had a car battery charger hooked to the motor and was only getting 9 volts out of it. This was until I moved the motor and it made contact, in which the wires were instantly fried!

What caused the voltage to be 9 volts across the pos/neg wires?
I guess you are implying it to be a 12 volt charger? Possibly the charger is not much more than a transformer with a full wave rectifier. Suppose you supplied a full wave rectifier with a 14v (peak) sinewave... neglecting losses, the output would be a series of half-sinusoids of peak amplitude 14v. If you use calculus (or a good ol' moving-coil meter), you will discover that the average of this rectified sinusoid is 9 volts. :wink: For a short time around the peaks a 14v sinusoid overcomes the car battery voltage, and forces charging current into the battery in short bursts.

I suggest that you continue to use a headlight globe in series with the charger during your experiments. This should protect the charger from damage due to overload. If your experimental motor shows no sign of working when the charger has a globe in series with it, then it's a safe bet it won't have worked had you overloaded the charger.
 
  • #31
NascentOxygen
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I had a car battery charger hooked to the motor and was only getting 9 volts out of it. This was until I moved the motor and it made contact, in which the wires were instantly fried!
Which wires melted? The wires coming from the charger, or the wires you soldered together to make the eggbeater?
 
  • #32
NascentOxygen
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To prove my concept, I tried to do this quick and dirty experiment, but it failed.
By failed do you mean there was no observable movement? What is the material in that catenary? It looks a lot like polycarbonate string. :confused:

Are you doing the test that I suggested OP should try?
 

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