Built an electric motor but missed something

[William123]

Hello!
I haven't read all that much about electrical engineering in school yet but I decided to build an electric motor since I enjoy doing this stuff. The problem is that when I connect it to an 11.1V battery that I had lying around, it just spazzes a little bit but it won't turn. I'm also guessing the amp draw is very high since the copper wire (coil) is 1.4mm in diameter (because if the resistance is low the amp draw must be higher, right?), and the cables got hot and there were sparks.

If you look at the picture you can see that I'm using small neodymium magnets which I suppose should be fine(?)
I know the construction might look ridiculous to you but it's my first time ever building something like this so be gentle.

Anyways, do I need to buy resistors to make this work or is there anything else I did wrong? (or even buy thinner wire which makes the resistance higher)
Is there a special way to do the winding of the wire?
The axle is supported by bearings so the magnets should be able to push it around i think.
(And let's not forget that english isn't my first language so let me know if I was unclear)

Picture: https://gyazo.com/593d9bcf7a51f12e0f9fc31434d0a80a

Thanks in advance! :)

 

[russ_watters]

What happens if you give it a little push?

 

[berkeman]

Hello!
I haven't read all that much about electrical engineering in school yet but I decided to build an electric motor since I enjoy doing this stuff. The problem is that when I connect it to an 11.1V battery that I had lying around, it just spazzes a little bit but it won't turn. I'm also guessing the amp draw is very high since the copper wire (coil) is 1.4mm in diameter (because if the resistance is low the amp draw must be higher, right?), and the cables got hot and there were sparks.

If you look at the picture you can see that I'm using small neodymium magnets which I suppose should be fine(?)
I know the construction might look ridiculous to you but it's my first time ever building something like this so be gentle.

Anyways, do I need to buy resistors to make this work or is there anything else I did wrong? (or even buy thinner wire which makes the resistance higher)
Is there a special way to do the winding of the wire?
The axle is supported by bearings so the magnets should be able to push it around i think.
(And let's not forget that english isn't my first language so let me know if I was unclear)

Picture: https://gyazo.com/593d9bcf7a51f12e0f9fc31434d0a80a

Thanks in advance! :)

Welcome to the PF.

I would recommend against using a big battery for your power supply for your first projects. The consequences of a mistake can be pretty bad (burst battery, acid all over the place, fire, burns, etc.).

A much better choice would just be a 12Vdc, 1A or 2A power supply "brick". You can pick them up pretty cheaply at Radio Shacks or other similar stores (or online). Can you get one of those?

 

[William123]

Welcome to the PF.

I would recommend against using a big battery for your power supply for your first projects. The consequences of a mistake can be pretty bad (burst battery, acid all over the place, fire, burns, etc.).

A much better choice would just be a 12Vdc, 1A or 2A power supply "brick". You can pick them up pretty cheaply at Radio Shacks or other similar stores (or online). Can you get one of those?

Should I power it from the wall? I actually found one 12Vdc 1.5A power supply that isn't being used. Should I give that a go?

Edit: @russ_watters I'm not sure if I want to try it again with that battery because of the heat and sparks :/

 

[berkeman]

Should I power it from the wall? I actually found one 12Vdc 1.5A power supply that isn't being used. Should I give that a go?

Yes, that's a much better choice.

Edit: @russ_watters I'm not sure if I want to try it again with that battery because of the heat and sparks :/

Good judgement on your part! With the wall-powered brick supply, you should be much safer in this project.

Can you post more diagrams of how you wound it, and how you made the commutator? Russ' suggestion of a light push is a good one, especially if your commutator has moderate gaps.

 

[berkeman]

I would recommend against using a big battery for your power supply for your first projects. The consequences of a mistake can be pretty bad (burst battery, acid all over the place, fire, burns, etc.).

BTW, don't ask me how I know this...

 

[meBigGuy]

Are the coils correctly connected? What happens if you reverse one coil? Or turn one magnet around? You will need to give it a spin, and try both directions.

You can follow the directions here:
http://holbert.faculty.asu.edu/wise/dcmotor.htm

 

[William123]

Yes, that's a much better choice.

Good judgement on your part! With the wall-powered brick supply, you should be much safer in this project.

Can you post more diagrams of how you wound it, and how you made the commutator? Russ' suggestion of a light push is a good one, especially if your commutator has moderate gaps.

Tried to be accurate but.. https://gyazo.com/68c9c0337ec3c4b49474ba21cddd1e93
I don't know exactly how the "brick" converters work but can the amp draw not exceed 1.5 amps if it says so on the back of the power supply?

Are the coils correctly connected? What happens if you reverse one coil? Or turn one magnet around? You will need to give it a spin, and try both directions.

You can follow the directions here:
http://holbert.faculty.asu.edu/wise/dcmotor.htm

Will definately try this if the power supply doesn't solve the problem :)

 

[sophiecentaur]

BTW, don't ask me how I know this...

I guess you have the scars to prove it?

 

[sophiecentaur]

Are the coils correctly connected? What happens if you reverse one coil? Or turn one magnet around?

That sounds like the answer - there are several combinations that won't work (or just work badly) - so go through the combinations systematically. The magnets should be NS-NS (or the reverse). IF you are getting sparks then you don't need to worry about the continuity of your wiring. The sense of the coil wiring is that the windings should both be clockwise or anticlockwise so that the whole length of coil is wound like a solenoid.
Sorry to ask and don't be offended, William, but is the wire enamelled (i.e. with insulating lacquer around it)? Several threads on this sort of topic have revealed that the OP is using plain copper wire, which is just a short circuit.

 

[William123]

That sounds like the answer - there are several combinations that won't work (or just work badly) - so go through the combinations systematically. The magnets should be NS-NS (or the reverse). IF you are getting sparks then you don't need to worry about the continuity of your wiring. The sense of the coil wiring is that the windings should both be clockwise or anticlockwise so that the whole length of coil is wound like a solenoid.
Sorry to ask and don't be offended, William, but is the wire enamelled (i.e. with insulating lacquer around it)? Several threads on this sort of topic have revealed that the OP is using plain copper wire, which is just a short circuit.

Yep it's enamelled (polyurethane). I'm going to try the power supply first though since the amp draw from the battery is high whether the axle is turning or not.

 

[sophiecentaur]

Yep it's enamelled (polyurethane). I'm going to try the power supply first though since the amp draw from the battery is high whether the axle is turning or not.

If trying all the combinations does no good (and you have checked for shorts) then your wire length may be too short. Using twice the length of wire with half the cross section could reduce the current draw and motor will still turn. Do you have access to a Multimeter, to measure the current?

 

[William123]

I tried the 12Vdc 1.5A power supply but it still spazzes like every half second, similar to the first attempt. Current should be passing through though since I was able to get a piece of metal stuck on both sides of the metal core (correct me if I'm wrong), although it was a bit weak imo. Should I try turning the magnets first and then redo the winding if turning the magnets doesn't work? Should I reverse one coil as meBigGuy said?

Edit: I should probably mention that the "spazz" is more like a pulse, sometimes it's strong and sometimes it's weaker. I don't know if this is because of the power supply or the winding. Probably the winding since it acted similarly when i used the battery.

Edit 2: I removed the wooden pieces that supported the magnets and held the magnets in my hands instead, but it didn't really matter which way I held them, it acted strange and I could feel the pulse with my fingers :S Probably going to have to try a different winding.

 

[sophiecentaur]

Should I reverse one coil as meBigGuy said?

That could help or . . . . Make the easiest change first. Real motors have iron cores in the armature so your coils are pretty weak electromagnets. What do you get when you put one of the magnets against one of the coils - on the table, connected directly and not on the motor? If you get no significant force that way then the motor won't go. My guess is that there are just not enough turns on the coils. If the coil magnet test works then I would suspect your wiring. Is it soldered well?

 

[William123]

What do you get when you put one of the magnets against one of the coils - on the table, connected directly and not on the motor?

I don't understand. If i put a magnet against the coil it stays there and the force is pretty strong. Could you draw?

 

[William123]

Now that I'm looking at the picture on the web page that @meBigGuy linked to I see that we have done the winding differently. I will try changing it later.

 

[berkeman]

I guess you have the scars to prove it?

More like scares, fortunately. I was very lucky several times...

 

[sophiecentaur]

I don't understand. If i put a magnet against the coil it stays there and the force is pretty strong. Could you draw?

OK. That's what I meant. If there is that much force between one magnet and one coil then there should be plenty to turn the motor. If the coils aren't being pulled to line up with the magnets then it looks as if one is pulling and one is pushing ??
Another point, though, have you got the phase of the commutator right? It should change the direction of the flow at the angle when the coils are just going past the magnets. That way, once the magnet has done its attracting job, it then starts to repel.

 

[William123]

OK. That's what I meant. If there is that much force between one magnet and one coil then there should be plenty to turn the motor. If the coils aren't being pulled to line up with the magnets then it looks as if one is pulling and one is pushing ??
Another point, though, have you got the phase of the commutator right? It should change the direction of the flow at the angle when the coils are just going past the magnets. That way, once the magnet has done its attracting job, it then starts to repel.

I tried winding it the way the picture was showing this time, but I'm still getting the pulse-thing (the thing is I'm not really feeling a repelling force, It's just attracting alot, then it attracts less, and sometimes the frequency of this "pulse" goes wild). I'm beginning to think that I should redesign the brushes since the current might be getting interrupted.
As for the commutator, I think it is correct. The "gap" is in line with the coils i guess you could say.
Thank you for sticking with me btw :)

 

[sophiecentaur]

As for the commutator, I think it is correct. The "gap" is in line with the coils i guess you could say.

Is it possible that the gaps, on either side (or the brushes) are not 180° separated and that both brushes happen to be contacting the same segment of the commutator? That would be be a short.
These suggestions of mine are what I would be looking for in my first 30 seconds of looking at the thing in real life. I am convinced that there's something really simple going on here. You are not permitted to give up now,

 

[William123]

Is it possible that the gaps, on either side (or the brushes) are not 180° separated and that both brushes happen to be contacting the same segment of the commutator? That would be be a short.
These suggestions of mine are what I would be looking for in my first 30 seconds of looking at the thing in real life. I am convinced that there's something really simple going on here. You are not permitted to give up now,

Just to give you a quick update: I removed the flat brushes and tried once with the cables themselves acting as brushes, unfortunately I only have two hands and wasn't able to perform a real test BUT I could definitely feel a repelling force this time! It turned almost 90° before the power cuts (the pulse thing is still there but I think it's because of bad contact). When the glue is dry I will do a real test to see if I can get rid of the pulse and get it to turn 360°.

Edit: I can't seem to get a continuous current going through.
- If there are no sparks, it repels for about a tenth of a second every half second
- If there are sparks it spazzes once for every spark
I actually did manage to get it to turn maybe 5 times but then it gave up. Should I try a different power supply or something? I don't know how I can further improve my brushes so..

 

[sophiecentaur]

I wonder about the contact that the brushes are making. They should not be making contact with both halves of the commutator at once so they need to have a convex face and the commutator should not have a dip between the segments (both these features will stop the brushes from touching both segments at once. I think the commutator segmnets should have a considerable gap between them if they can't be machined like they are in a 'real' electric motor. Motor brushes are usually made of carbon so that the contact resistance increases as the contact area reduces to zero - just before changeover. This means that the current is not broken all at once and there are fewer sparks.

 

[William123]

They should not be making contact with both halves of the commutator at once so they need to have a convex face and the commutator should not have a dip between the segments

So is this gif http://pcbheaven.com/wikipages/images/howdcmotorworks_1269637339.gif correct or incorrect? When the segments turn gray in the gif, isn't that a short? I tried to avoid that. I could try making a new commutator and brushes that are convex and be more careful this time.

 

[sophiecentaur]

So is this gif http://pcbheaven.com/wikipages/images/howdcmotorworks_1269637339.gif correct or incorrect? When the segments turn gray in the gif, isn't that a short? I tried to avoid that. I could try making a new commutator and brushes that are convex and be more careful this time.

The author mentions this in the text and tells us that he will explain the short circuit problem later .( I think it could have been presented better.) The three coil motor doesn't have the problem. A simple, two coil, motor should not have a brush arrangement as shown in the diagram. Many of the student built motors just have wires, acting as a commutator and wide brushes to extend the contact angle a bit but the connect time is short and not optimal. You are better off having a reduced average torque and avoiding excess current / sparks / PSU problems so try to modify your commutator and brushes to take into account of all this.

 

[meBigGuy]

when I built one of these in high school, we used simple wires as the commutator. The wires have to make contact at the right point to cause a repulsion force without slowing the motor before the rotors align with the magnet. You could probably experiment with slightly wider commutation to get a little more force.

The way I picture it would be that the rotor goes slightly past the magnet and then the commutator makes contact and pushes the rotor away in the same direction it was traveling. But I don't remember that for sure.

 

[William123]

The author mentions this in the text and tells us that he will explain the short circuit problem later .( I think it could have been presented better.) The three coil motor doesn't have the problem. A simple, two coil, motor should not have a brush arrangement as shown in the diagram. Many of the student built motors just have wires, acting as a commutator and wide brushes to extend the contact angle a bit but the connect time is short and not optimal. You are better off having a reduced average torque and avoiding excess current / sparks / PSU problems so try to modify your commutator and brushes to take into account of all this.

when I built one of these in high school, we used simple wires as the commutator. The wires have to make contact at the right point to cause a repulsion force without slowing the motor before the rotors align with the magnet. You could probably experiment with slightly wider commutation to get a little more force.

The way I picture it would be that the rotor goes slightly past the magnet and then the commutator makes contact and pushes the rotor away in the same direction it was traveling. But I don't remember that for sure.

I'll try to improve the commutator and brushes tomorrow. But let's forget about rotation for a moment. If I were to solder the cables directly to the commutator then in no way should the electromagnetic force be pulsating, right? Cause I believe it would if I did, which kind of makes me believe I should swap out the power supply. But that'll be after I've made the Commutator 2.0. I appreciate the replies :)

 

[William123]

It's been a while now and I haven't been able to tinker very much with the motor but the other day I threw away the power supply and tried with a 9V battery instead and voilà. I also added two coils and split the commutator into 4 parts to avoid shorts. I have ordered a voltage regulator and a resistor so that I can use my bigger battery without having any heat issues.

I have a new question now though. If current is what determines an electromagnet's strength, should I just go for the lowest possible voltage? I might not be able to do this in practice but doesn't higher voltage mean lost power (heat)? I ordered a 1 ohm resistor and the resistance of the motor plus cables might be around 0.3 ohm or less (don't quote me on this), so the amp draw will be about 6A at about 8V. But wouldn't I get more out of my battery if I went for the lowest possible resistance (only the resistance of the copper wiring for example) and the lowest possible voltage, while the amp draw is still 6A?

If the resistance of the motor and cables is 0.33 ohm then the amp draw will be 6A at about 2V. I don't know if the voltage regulator can reduce the voltage that much since I haven't used one before. Will the battery last longer if I put aside the resistor and just lower the voltage further?

Thanks

 

[sophiecentaur]

If the resistance of the motor and cables is 0.33 ohm then the amp draw will be 6A at about 2V.

This will only be the current when the motor is stalled and immediately at startup. As soon as it is moving, there will be a back emf produced and the current will (should) drop noticeably. The speed can build up until the mechanical output and friction losses plus any restive losses will balance the power drawn from the supply. Your 6A could drop to a fraction of an amp if your motor is well designed.

 

[William123]

This will only be the current when the motor is stalled and immediately at startup. As soon as it is moving, there will be a back emf produced and the current will (should) drop noticeably. The speed can build up until the mechanical output and friction losses plus any restive losses will balance the power drawn from the supply. Your 6A could drop to a fraction of an amp if your motor is well designed.

Interesting. I tried connecting the 11V battery for a couple of seconds for the sake of testing and it was turning so fast (this was with two coils though, I removed the other two because it didn't turn as well with them, maybe the 9V battery got tired)!

I'd like to do some measurements with a multimeter while it is running to see if this is safe. I suppose not but.. The voltage regulator that I ordered shows both volts and amps if I remember correctly so I could come back with the results soon. Thank you for all your replies! :D

 

[sophiecentaur]

Interesting. I tried connecting the 11V battery for a couple of seconds for the sake of testing and it was turning so fast (this was with two coils though, I removed the other two because it didn't turn as well with them, maybe the 9V battery got tired)!

I'd like to do some measurements with a multimeter while it is running to see if this is safe. I suppose not but.. The voltage regulator that I ordered shows both volts and amps if I remember correctly so I could come back with the results soon. Thank you for all your replies! :D

If you can get hold of a low voltage motor and do the same sort of measurements on that, you might find it interesting to compare. A commercial motor will definitely show a big difference between stall current and running current.