Home-made electrical motor not running

  • #1
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1
Summary:
For school, I am trying to make an electric motor. When I try to apply power across the commutator however, it will either twitch a little bit or do nothing at all.
Here are the details. I started with a nut and bolt, and drilled a hole down the center of it. I inverted and glued into place a carbon fiber rod in the hole. I glued a bit on the end of the bolt. I wrapped magnet wire around the bolt on each side of the rod 400 times. I made a commutator using brass, and soldered one end of the wire to each side. The separation in the commutator is lined up the the bolt head and nut.

For magnets, I am using two small (but strong) magnets per side.

For power, I am using a 9-volt battery with copper wires connected to it. I’m touching the copper wires against the commutator 180 degrees apart.

The structure is made out of aluminum, if that matters.

What am I doing wrong? Am I missing anything obvious?

let me know if you want more info or pictures.

B24A0DE0-5188-467D-A209-4DA0AE3A2C2D.jpeg

5490C9FA-B9F7-4439-87E0-23539F73744A.jpeg
372B287F-2FCD-49E5-ADFF-359A6A4E0686.jpeg
 

Answers and Replies

  • #2
23
1
Summary:: For school, I am trying to make an electric motor. When I try to apply power across the commutator however, it will either twitch a little bit or do nothing at all.

Here are the details. I started with a nut and bolt, and drilled a hole down the center of it. I inverted and glued into place a carbon fiber rod in the hole. I glued a bit on the end of the bolt. I wrapped magnet wire around the bolt on each side of the rod 400 times. I made a commutator using brass, and soldered one end of the wire to each side. The separation in the commutator is lined up the the bolt head and nut.

For magnets, I am using two small (but strong) magnets per side.

For power, I am using a 9-volt battery with copper wires connected to it. I’m touching the copper wires against the commutator 180 degrees apart.

The structure is made out of aluminum, if that matters.

What am I doing wrong? Am I missing anything obvious?

let me know if you want more info or pictures.

View attachment 291165
View attachment 291166View attachment 291167
Let me also add that I checked the copper wire and brass commutator with a multimeter, and had a little less than 20 ohms of resistance across the system.
 
  • #3
Drakkith
Staff Emeritus
Science Advisor
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Does your wire have an insulating coating on it? If not, you're just shorting the whole thing out.
 
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  • #4
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I’m Does your wire have an insulating coating on it? If not, you're just shorting the whole thing out.
I think so. It was advertised as having a coating.
image.jpg
 
  • #5
marcusl
Science Advisor
Gold Member
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Is your coil wound continuously from one end to the other? What are the nut and bolt made of? (They should be plain steel, not stainless.) You don’t show the orientation of your brushes (contacts)—they should contact side to side, not top to bottom, because the coil (armature) wants to change electrical polarity just at the point you are showing. Finally, you could give it a spin with your finger after connecting the brushes to start it moving. Make sure your battery is fresh, too.
 
  • #6
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You grabbed the strongest magnet at hand, I guess?

In this setup the magnets are trying to hog the iron and you would need current through the coil strong enough to rival that force.

I would try reduce the amount of magnets and extend the magnetic field (and make it more homogenous), maybe by some iron plates.
Also, how is the polarity of the magnets?
 
  • #7
tech99
Gold Member
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Check that the magnets are attracting each other, in other words, N at one end of the bolt and S at the other.
Commutator must be altered as mentioned.
You need to give the motor a good spin top start it because the magnets attract the bolt even with no current.
A 9V battery might not give enough current due to its internal resistance. Maybe use 4 x AA batteries in series giving about 6 volts. I usually use an air coil for the armature.
 
  • #8
Baluncore
Science Advisor
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@S_Noakes
Is there a web link to the instructions you were given?
 
  • #9
tech99
Gold Member
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Check that the magnets are attracting each other, in other words, N at one end of the bolt and S at the other.
Commutator must be altered as mentioned.
You need to give the motor a good spin top start it because the magnets attract the bolt even with no current.
A 9V battery might not give enough current due to its internal resistance. Maybe use 4 x AA batteries in series giving about 6 volts. I usually use an air coil for the armature.
It is also possible that the shaft is too thick, which increases friction. Best to use a small diameter shaft.
 
  • #10
23
1
Is your coil wound continuously from one end to the other? What are the nut and bolt made of? (They should be plain steel, not stainless.) You don’t show the orientation of your brushes (contacts)—they should contact side to side, not top to bottom, because the coil (armature) wants to change electrical polarity just at the point you are showing. Finally, you could give it a spin with your finger after connecting the brushes to start it moving. Make sure your battery is fresh, too.
1) yes, the coil is wound continuously from one side to the other

2) the nut and bolt ARE stainless. How would this affect things?

3) picture included below. Mine is the same way. The “cuts” in the brushes face the nut and the head of the bolt

4) I have tried giving it a boost with my finger. No luck.
46C47730-7696-4B08-AA7C-3EE02D91F03C.png
 
  • #11
23
1
You grabbed the strongest magnet at hand, I guess?

In this setup the magnets are trying to hog the iron and you would need current through the coil strong enough to rival that force.

I would try reduce the amount of magnets and extend the magnetic field (and make it more homogenous), maybe by some iron plates.
Also, how is the polarity of the magnets?
1) they were the strongest magnets I could find.

2) where would I add the iron plates? Horizontal to the base of the motor, at the same height the magnets are currently?

3) the polarity of the magnets is north on one side and south on the other
 
  • #13
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1,412
2) where would I add the iron plates?
The original context of that coil you brought up as template is something like this:
513Ml6g55RL._AC_SL1000_.jpg

With this setup the magnets cannot 'hog' the screw, since the magnetic circuit is always closed, without singular positions.
Try to reproduce this as much as you can.

Or, you can drop the screw and use a wooden stick instead. That will work too.
 
  • #14
23
1
The original context of that coil you brought up as template is something like this:
View attachment 291191
With this setup the magnets cannot 'hog' the screw, since the magnetic circuit is always closed, without singular positions.
Try to reproduce this as much as you can.

Or, you can drop the screw and use a wooden stick instead. That will work too.
I’ll give that a shot after I get back from school. Thanks!
 
  • #15
Baluncore
Science Advisor
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2) the nut and bolt ARE stainless. How would this affect things?
Stainless steel is not usually magnetic. Test it with a magnet and compare it to a cheap bolt.
I expect the cheapest soft iron bolt would perform much better than any more expensive bolt.
 
  • #16
23
1
Stainless steel is not usually magnetic. Test it with a magnet and compare it to a cheap bolt.
I expect the cheapest soft iron bolt would perform much better than any more expensive bolt.
Didn’t know that stainless was less magnetic than iron. I’ll see if I can track down a soft iron nut and bolt. All of the hardware stores around me only carry the stainless stuff
 
  • #17
Baluncore
Science Advisor
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All of the hardware stores around me only carry the stainless stuff
The silver surface could be zinc plate on a carbon steel bolt, which should not be a problem.
I cannot read what is written on the head of the bolt you used. What does it say?
If the bolt head is marked 304 or 316 then it is stainless steel and will need to be changed.
 
  • #18
23
1
The silver surface could be zinc plate on a carbon steel bolt, which should not be a problem.
I cannot read what is written on the head of the bolt you used. What does it say?
If the bolt head is marked 304 or 316 then it is stainless steel and will need to be changed.
The head of the bolt says A2-70 and “THE”. What number bolt is the best?
image.jpg
 
  • #19
23
1
The silver surface could be zinc plate on a carbon steel bolt, which should not be a problem.
I cannot read what is written on the head of the bolt you used. What does it say?
If the bolt head is marked 304 or 316 then it is stainless steel and will need to be changed.
Here’s the bag it came out of
image.jpg
 
  • #20
Baluncore
Science Advisor
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They are stainless steel.
"THE" is the manufacturer registration code, which makes failures traceable.
Google A2-70 and you will get; "When we say A2-70 it generally means that the bolt / screw is from SS 304 grade and has an ultimate tensile strength as 70 kg or 700 n/mm2."

You must replace the bolt with mild or carbon steel. Use the cheapest lowest grade available.
I don't know your supplier so I don't know the national numbers used.
 
  • #21
23
1
The silver surface could be zinc plate on a carbon steel bolt, which should not be a problem.
I cannot read what is written on the head of the bolt you used. What does it say?
If the bolt head is marked 304 or 316 then it is stainless steel and will need to be changed.
I looked into it and the A2 signifies 304, while 70 is related to the hardness. What number is recommended?
 
  • #22
23
1
They are stainless steel.
"THE" is the manufacturer registration code, which makes failures traceable.
Google A2-70 and you will get; "When we say A2-70 it generally means that the bolt / screw is from SS 304 grade and has an ultimate tensile strength as 70 kg or 700 n/mm2."

You must replace the bolt with mild or carbon steel. Use the cheapest lowest grade available.
I don't know your supplier so I don't know the national numbers used.
Posted at almost the exact same time. Oops. Lowe’s is my main supplier, but Home Depot and Ace Hardware are also options
 
  • #23
1,073
309
@S_Noakes , forget the bolt markings, just take one of your neodymium magnets and stick it to the bolt with your fingers, if the magnet doesn't stick, then it;'s stainless if it sticks then it;'s iron. You can use the same technique in store before buying the bolts, just take the right size bolt you want and apply a magnet test.

Other simple points to make. First of all your shaft bearings seem like made out of bolt nuts from what I can tell , what is your shaft made from , metal?
Now bolt nuts are very bad bearings, they have sharp grooves and high friction which might be one reason nothing wants to move.
I suggest just find a piece of plastic that is one of those slippery ones like on some food packaging , attach it to your frame, and make a hole which is just a bit larger than your shaft. Get a few drops of cooking oil on the shaft where it meets the plastic and you will be far better off than with these metal bolt nuts.

Another thing, do you have a compass ? If not take one of your magnets (just one) label one side of the magnet (one pole) with a marker and apply current to your coils, then put the labeled magnet side to each side of the rotor and see , one side should repel the magnet , the other side should attract it, this way you can know whether your wire wound direction is correct because maybe you have wound the wire in wrong directions and your rotor has the same pole on each end?


Also check whether your stationary magnets are correct polarity, different pole on each side.


Also remember this is a two pole motor, two pole motors have lower torque than motors with more poles like 4,6, etc. The reason is because each pole has to push/pull for a longer distance/ more degrees, than if there were more poles.

Finally check the placement of your commutator, as others pointed out. It is crucial at which point the current is switched , if if happens at the wrong moment instead of a motor you simply get an electromagnet which could also be the reason why nothing turns and everything sticks.


Finally if you can maybe you can get a hold of a smaller lighter car battery , 12v DC.
12v Dc is safe but a car battery is much more rugged and fully charged will give you much time to play around , tests for errors. A 9v flat handheld battery will dry out fast and can also get hot because it's small and has poor heat sinking.
 
  • #24
23
1
@S_Noakes , forget the bolt markings, just take one of your neodymium magnets and stick it to the bolt with your fingers, if the magnet doesn't stick, then it;'s stainless if it sticks then it;'s iron. You can use the same technique in store before buying the bolts, just take the right size bolt you want and apply a magnet test.

Other simple points to make. First of all your shaft bearings seem like made out of bolt nuts from what I can tell , what is your shaft made from , metal?
Now bolt nuts are very bad bearings, they have sharp grooves and high friction which might be one reason nothing wants to move.
I suggest just find a piece of plastic that is one of those slippery ones like on some food packaging , attach it to your frame, and make a hole which is just a bit larger than your shaft. Get a few drops of cooking oil on the shaft where it meets the plastic and you will be far better off than with these metal bolt nuts.

Another thing, do you have a compass ? If not take one of your magnets (just one) label one side of the magnet (one pole) with a marker and apply current to your coils, then put the labeled magnet side to each side of the rotor and see , one side should repel the magnet , the other side should attract it, this way you can know whether your wire wound direction is correct because maybe you have wound the wire in wrong directions and your rotor has the same pole on each end?


Also check whether your stationary magnets are correct polarity, different pole on each side.


Also remember this is a two pole motor, two pole motors have lower torque than motors with more poles like 4,6, etc. The reason is because each pole has to push/pull for a longer distance/ more degrees, than if there were more poles.

Finally check the placement of your commutator, as others pointed out. It is crucial at which point the current is switched , if if happens at the wrong moment instead of a motor you simply get an electromagnet which could also be the reason why nothing turns and everything sticks.


Finally if you can maybe you can get a hold of a smaller lighter car battery , 12v DC.
12v Dc is safe but a car battery is much more rugged and fully charged will give you much time to play around , tests for errors. A 9v flat handheld battery will dry out fast and can also get hot because it's small and has poor heat sinking.
Thanks for your response.

1) the nuts aren’t bearings, they are glued to the shaft to prevent it from moving side to side.

2) the bolts I have currently are magnetic, but very weakly.

3) I have verified that the magnet poles are correct (north on one side, south on the other)

4) how should the commutator be oriented? Could someone post a picture that I can try to emulate?

5) I have been using a wall-plug power supply that produces 13.8 volts and 3 amps for testing purposes.
 
  • #25
Baluncore
Science Advisor
10,082
4,438
I guess you are in USA.
Lowe's stock = Hillman, Zinc-Plated, Hex Bolt; In the size you need.
 

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