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

[Flyingwing12]

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 ;)

 

[dlgoff]

You need to be able to continuously switch the current direction; coil attracted to magnet then repelled from magnet. This is accomplished on dc motors by using Commutator and Brushes.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html

 

[Bobbywhy]

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

 

[Flyingwing12]

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.

 

[Flyingwing12]

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?

 

[I_am_learning]

Can you post a picture of your setup?
Wires melting is clearly a problem. Either use lower Voltage or huge thinner wires.

 

[I_am_learning]

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.

 

[Flyingwing12]

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

 

[I_am_learning]

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.

 

[davenn]

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

 

[Flyingwing12]

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.

 

[Averagesupernova]

Flyingwing12, before we go on I would ask you if you know what a commutator does.

 

[Flyingwing12]

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...

 

[NascentOxygen]

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.

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

 

[Averagesupernova]

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?

 

[Flyingwing12]

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.

 

[Flyingwing12]

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 :)

 

[NascentOxygen]

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. 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. 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!

 

[Averagesupernova]

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.

 

[NascentOxygen]

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.

 

[Flyingwing12]

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.

 

[Flyingwing12]

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.

 

[NascentOxygen]

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. Motors use lots of coils to produce strong magnetic fields.

 

[NascentOxygen]

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.

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!

 

[dlgoff]

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.

edit: removed emoticon link

Anyway,

https://www.youtube.com/watch?v=Ue6S8L4On-Y

 

[I_am_learning]

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.

 

[I_am_learning]

To prove my concept, I tried to do this quick and dirty experiment, but it failed.

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

 

[dlgoff]

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.

 

[Flyingwing12]

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?

 

[NascentOxygen]

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. 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.

 

[NascentOxygen]

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?

 

[NascentOxygen]

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.

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

 

[I_am_learning]

its working now. http://www.youtube.com/watch?v=D1GpgefYeIs&feature=youtube_gdata_player

 

[NascentOxygen]

its working now. http://www.youtube.com/watch?v=D1GpgefYeIs&feature=youtube_gdata_player

Well done, I_am_learning! That's a convincing demonstration.

If you soldered (or twisted) another semicircular piece onto that, to complete the ring, it should spin faster and more smoothly. Current drain will go up, though.

 

[uart]

While we're posting videos of our home made motors... Here's one I made some years ago as a demonstration for my students.

http://www.youtube.com/watch?v=yEFapvHCpgs&feature=youtu.be

 

[Flyingwing12]

Everybody hold their horses before we lose focus.

I have included a diagram of fairly accurate measurements regarding my design layout.

I don't have the information of the car battery because they could all be different depending on a lot of factors. But I am assuming that it is a perfect battery :P

Will a regular 60 watt bulb work in this series setup? I was wondering if the 60 watts was coming from the suggested 120v usage.

I realize that my calculations are excluding the Bulb which would obviously reduce current. But I Don't know what the readings for the bulb will be. Any help is appreciated.

If I can get this series setup to work. Then I can worry about finding out how powerful of a magnet I will need.

 

[NascentOxygen]

Will a regular 60 watt bulb work in this series setup? I was wondering if the 60 watts was coming from the suggested 120v usage.

A 60w 120v bulb has a resistance around 240Ω. (V*V/R = 60)

This is a new rotor you have wound, is it? One that has 130Ω resistance? How many turns of wire?

I realize that my calculations are excluding the Bulb which would obviously reduce current. But I was in the moment and thought " What the heck"

If I can get this series setup to work. Then I can worry about finding out how powerful of a magnet I will need.

If you add 240Ω in series with your new rotor of 130Ω then it will reduce the current but I'd expect the rotor will still turn. However, with a rotor of 130Ω there is no necessity to "protect" the battery, except against accidental short-circuits. If the rotor gets hot and starts smoking, then that means 12v is too much for it, and you can incorporate some series resistance like you've shown, to reduce the voltage that the rotor sees. But 130Ω is nothing like a short-circuit, so the car battery won't be overloaded.

Once it starts spinning, the "slip-ring" contacts you have will impose their own resistance to current flow, so that 130Ω will be further increased, and the motor will draw less current once it gets spinning.

You have now abandoned the idea of getting your original egg-whisk rotor to turn?

 

[Flyingwing12]

no, I just need a really strong Magnet.

 

[Flyingwing12]

But the Bulb would be hooked up to 12v. So the wattage and current would be different right?

The setup I tried earlier was having the whole thing in series, without a lamp to reduce current, which was probably 2 amperes. The volt meter showed only 9vdc coming from the battery charger. But I should be using something else. The car charger was explained to have a rectifier that was making short jumps of current. Cutting to the chase, the small 1/16th copper wires leading form the sides of my motor melted and I was not surprised.

The eggbeater is shown on page 1 I think. It is only one continuous line of 5/64 inch copper wire.

I know there is a way to make this work. I was able ot get a similar design of smaller scale to work. SO why wouldn't this?

BTW FOR ANYONE WHO CAN ANSWER: My multimeter has Ohm settings of 20,200,200k, and 2000k. Why are these in 2's?

Also, my multimeter never seems to stick to one reading on Ohms. it always jumps between a high and low number. How can I get it to give me a straight reading?

I'm using a cheap 30 dollar multimeter form sears btw.

 

[NascentOxygen]

But the Bulb would be hooked up to 12v. So the wattage and current would be different right?

Sure they'll be different.

The eggbeater is shown on page 1 I think. It is only one continuous line of 5/64 inch copper wire.

Are you saying that half a dozen pieces of 5/16 inch copper wire soldered in parallel give a resistance of 120Ω?? Not likely.

Also, my multimeter never seems to stick to one reading on Ohms. it always jumps between a high and low number. How can I get it to give me a straight reading?

When you connect a resistor or lightbulb or anything across your meter, the resistance reading jumps around and never settles?

 

[NascentOxygen]

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.

You could try bar magnet(s).

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

On DC motors, the function of the commutator is to allow current in only the rotor winding that is most effective in maintaining rotation at that particular moment. In your egg whisk rotor, current in the upper wire is not aiding rotation (it's slightly opposing it), so allowing that current is counter-productive.

You could retrofit a commutator to your rotor (see my sketch). Cut the rotor wires near one of the hubs and rejoin each in a strong mechanical joint using heat-shrink tubing, while at the same time ensuring that there is no electrical connection inside that join. You have 8 wires, you need to cut and rejoin in a total of 7 places. (You could do 8, but 7 is exactly as good.) Perhaps include a tiny piece of matchstick inside the heat-shrink to keep the two ends of the wires apart.

You make this modification at only one end of the rotor wires, so that's 7 cuts-and-rejoins needed. This now means that electricity can't get into that end of the rotor via the axle, so remedy this with a flexible bare copper wire bent into a J-shape and positioned so it will make good contact with that end of the one rotor wire nearest the magnet. You can hold this sliding contact in your hand while you optimize its shape and positioning, for maximum rotational speed.

As I cautioned, if your egg whisk rotor shows no inclination to move, then increasing the current or adding a commutator will not change this.

Happy experimenting! https://www.physicsforums.com/images/icons/icon14.gif

 

[Flyingwing12]

I am following the design process. But I am not seeing how you're J shaped wire will work. The motor is supported by two copper pylons. The pylons are about an inch and a half wide, so the wire would need to touch the pylon right?

Here is what I think you're sketch is telling me to do.

 

[Flyingwing12]

It also goes through two pylons of copper that support this eggbeater. The cooper is also oxidized. So the resistance should be a tad higher than pure silky clean Cu.

The ohm meter jumps around when I measure the resistance of wires. It usually jumps form 168-30 and then quickly stops at .3Ω and I have a belief that the resistance is probably lower than that.

But hey, how accurate is a 30 dollar meter going to be?

Still don't know why they marked all the measurements off in twos...

 

[NascentOxygen]

I am following the design process. But I am not seeing how you're J shaped wire will work. The motor is supported by two copper pylons. The pylons are about an inch and a half wide, so the wire would need to touch the pylon right?

Here is what I think you're sketch is telling me to do.

You have to disconnect the voltage from the support at this end, and instead feed the current into the ribs of the rotor by means of a rubbing contact using springy wire. The springy wire needs to rub against that part of the egg beater to the left of the heat-shrink so that as the rotor turns, current switches to a new rib of thick copper wire, goes along that rib and out of the motor at the support at the other end.

I'm using the word "rib" to describe anyone of the thick wires comprising the egg whisk.

 

[SirAskalot]

One word; Homopolar motor. Actually that is two words, non the less it might be a good/better solution than your design, because you don't need a commutator. Google it.

You also might want to skip the car battery, it gives a pretty nasty arc if its shorted. And can result in injury. Since it just going to rotate in free air without any loading, for a short time, regular (D-cell, 9V, 4.5V etc) batteries would be sufficient.

 

[NascentOxygen]

I am following the design process. But I am not seeing how you're J shaped wire will work.

The J shaped wire is a sliding contact to "brush" against the rotor and put current into the rib that at that moment is closest to the magnet.

 

[dlgoff]

The J shaped wire is a sliding contact to "brush" against the rotor and put current into the rib that at that moment is closest to the magnet.

Brushes? What's next, ... a commutator?