Engineering Homemade DC electric motor not working

[Ranveer]

Homework Statement

I have made a DC motor at home and it is not working

Relevant Equations

I have used 4 magnets on each side, and the commutator is made up of 2 sheets of copper placed parallel to each other.
Used 4, 9V batteries and see sparks but the shaft is not moving whatsoever even with a running start

Summary : i have tried changing the batteries and wire,but still nothing. The wire is insulated and the coating is removed at the ends of the battery and the point where the wire touches the commutator. I have not counted the number of coils. This is required for a school project. If someone has idea what's wrong please help. Thank you.

 

[tech99]

Several possibilities.
1) The batteries you are using cannot deliver the big current required. Try D cells.
2) The armature bolts are very long, so that the push they receive from the magnets is very brief.
3) I am uncertain how you have wound the armature bolts because I see three wires crossing at the centre. The two windings must be in the same sense and the wire must not be doubled into a U-shape before winding.
4) Friction is a problem with home made motors, especially as the armature looks a bit heavy, and the commutator often has too much friction.
5) As you use a iron core for the armature, this will be attracted to the magnets (by induction) when the motor is stationary and the motor has to be spun fast to overcome this pull.
6) The gaps between the magnet and the ends of the armature are quite large.

 

[berkeman]

Welcome to PF.

see sparks but the shaft is not moving whatsoever even with a running start

Where did you get this design idea from? Was there a video of this design actually working in that source?

 

[Ranveer]

Welcome to PF.Where did you get this design idea from? Was there a video of this design actually working in that source?

Yes, i referred to an very old video

 

[Ranveer]

Several possibilities.
1) The batteries you are using cannot deliver the big current required. Try D cells.
2) The armature bolts are very long, so that the push they receive from the magnets is very brief.
3) I am uncertain how you have wound the armature bolts because I see three wires crossing at the centre. The two windings must be in the same sense and the wire must not be doubled into a U-shape before winding.
4) Friction is a problem with home made motors, especially as the armature looks a bit heavy, and the commutator often has too much friction.
5) As you use a iron core for the armature, this will be attracted to the magnets (by induction) when the motor is stationary and the motor has to be spun fast to overcome this pull.
6) The gaps between the magnet and the ends of the armature are quite large.

Thank you for the suggestions.
The armature bolt is a 4 inch long bolt.
I wound the string by starting at one end and moving towards the end of the bolt, then I moved from under the pipe to the other side, when I reached the end of the other side I wound it again towards the starting point. Basically the wire is wound from left to right, and again right to left, acting oppositely with the wire below it.

The gaps between the bolt and the magnets are barely an inch long.

Another question is is, is the number of woundings important to the amount of voltage it needs to run?

 

[tech99]

The winding must have the same sense of rotation on both arms.
The one inch gap seems much too long, it needs to be a small gap.
The number of turns is very important, a few hundred turns is required.
I think the main problem is that the very small diameters of magnets and armature bolts mean the there is only a very short mechanical impulse.

 

[tech99]

There is a very simple motor described in this video and we use it at the school.

 

[Ranveer]

There is a very simple motor described in this video and we use it at the school.

I asked the professor about this, he said it needs to be bigger in size, that's why I choose a larger model.

 

[Ranveer]

The winding must have the same sense of rotation on both arms.
The one inch gap seems much too long, it needs to be a small gap.
The number of turns is very important, a few hundred turns is required.
I think the main problem is that the very small diameters of magnets and armature bolts mean the there is only a very short mechanical impulse

So what I'll do is buy a few bigger magnets and shorten the size of the bolt, I have a 3 inch bolt that I can use.

Also how do I wind the wire, if I keep it the same direction (from left to right) do I start winding again from the beginning of the bolt (from the left) or start from the place I ended (the right side of the bolt).

 

[marcusl]

Just keep going from one end all the way to the other as though there is no axle in the center.

 

[Baluncore]

Also how do I wind the wire, if I keep it the same direction (from left to right) do I start winding again from the beginning of the bolt (from the left) or start from the place I ended (the right side of the bolt).

Stick, or tie with a thread, the start of the winding to the middle of the bolt.
Hold one end of the bolt in the chuck of a cordless drill, (that turns in only one direction).
Wind the wire onto the bolt from the centre to one end, then as a second layer, back to the centre. Jump over the centre, then keep going to the end of the bolt with a first layer, then back to the centre as a second layer.
You then have a neat, two layer coil wound onto the bolt. The ends of the wire are at the centre, where they can be connected to the commutator. If you wind it neatly, the weight distribution of the wire, will be close to balance.

 

[Ranveer]

Stick, or tie with a thread, the start of the winding to the middle of the bolt.
Hold one end of the bolt in the chuck of a cordless drill, (that turns in only one direction).
Wind the wire onto the bolt from the centre to one end, then as a second layer, back to the centre. Jump over the centre, then keep going to the end of the bolt with a first layer, then back to the centre as a second layer.
You then have a neat, two layer coil wound onto the bolt. The ends of the wire are at the centre, where they can be connected to the commutator. If you wind it neatly, the weight distribution of the wire, will be close to balance.

Is this only limited to 2 layers or can I do more layers with this method?

 

[Ranveer]

Just keep going from one end all the way to the other as though there is no axle in the center.

Thanks for the suggestions, I'll try the other method as well tland use the one which works better

 

[DaveC426913]

It is very difficult for us to troubleshoot just by eye.

Can you elaborate on how it is not working?

1. Does it simply not move at all, or does it move a tiny bit and stop? Ah. "the shaft is not moving whatsoever even with a running start"
2. When you manually move the armature while it's in operation, can you feel the attractive force as it approaches the stator and can you feel the replusive foce as it passes the stator? IOW, is it trying to work the way it should?
3. What else can you tell us that might help zero in on the point of failure?

 

[Baluncore]

Is this only limited to 2 layers or can I do more layers with this method?

So long as you keep winding the same way, you can have more layers. In general, for higher voltages, a motor or generator will have more turns of thinner wire.

If the winding starts and ends at the centre, and you wind it neatly and balanced, there will be an even number of layers.

 

[Ranveer]

It is very difficult for us to troubleshoot just by eye.

Can you elaborate on how it is not working?

1. Does it simply not move at all, or does it move a tiny bit and stop? Ah. "the shaft is not moving whatsoever even with a running start"
2. When you manually move the armature while it's in operation, can you feel the attractive force as it approaches the stator and can you feel the replusive foce as it passes the stator? IOW, is it trying to work the way it should?
3. What else can you tell us that might help zero in on the point of failure?

So what I did was I removed the coiling, and re did it from the center, now both sides have 400 coils each.

I have connected the live wire to the armature and I don't feel any repulsive force, on both the sides, where the metal bolt is going up or down it gets attracted towards the magnet even when it's connected to power.

The circuit works as I see sparks on a metal plier, but don't see any effect on the wire that's on the armature
The winded wire does not get hot even while it's powered.

The magnets are connected like [<NS> <shaft> <NS>]

Another thing might be the metal used for commutator, i have used a copper pipe that I had found in school.

Google says I need to use an alloy of steel,
So that could be one issue, but there are many more.

 

[Tom.G]

The magnets are backwards. The N pole on one should be facing the S pole on the other one.

Without power applied, inspect the brush/armature alignment to make sure that both brushes never contact the same armature segment during a complete rotation.

By the way, a simple 2-pole motor like this will NOT start on its own! You will have to give it a good spin by hand to get it running.

The batteries are connected in series which means their voltages add but their current capability remains the same as one battery. I would expect this motor to require a rather high current to operate. I suggest the batteries be connected in parallel, all the "+" connected together and all the "-" connected together. The result will be 9V but with four times the current capability.

Better yet, take the advice of @tech99 in post #2 and use 2 to 4 "D" cells in series; they are more difficult to connect to though.
You might have to make a battery holder by nailing some metal strips to a piece of wood, then use rubber bands to hold the strips in contact with each battery. Much easier if you contact each battery individually, they won't stay in line if you place them head-to-tail as in a flashlight!

By the way, if you do not have a voltmeter to test the 9V batteries, here is a simple test. Using a single 9V battery, briefly touch the contacts to the top of your tongue just behind the tip.
a) If you sorta wish you hadn't done that, the battery is new
b) If you feel a substantial tingling and maybe a slight sour taste, it's "Usable"
c) Mild tingling, probably not much good for anything
d) No or very slight tingling, or an acid taste, dead

If the suggestions from everyone so far do not get it running, here is another simple test to help track down the problem.

1) Find a couple somethings, maybe screwdriver or plyers, made of Iron or Steel.
We want them NOT magnetized, so bring them in contact with each other then gently separate them. If they feel like they stick together then one or both of them are magnetized. Try other items from your tool box, or even some nails, until you find two Iron or Steel things that don't attract each other. They don't have to be the same shapes.

2) With no power to the motor, position the motor armature so the bolt is vertical, farthest away from the magnets. Now bring one of the Iron/Steel items to one end of the bolt. If it is attracted that means the armature is magnetized; remember how strong the attraction is, you will need it for comparison in the next step. Not to worry whether magnetized or not right now, it could have been magnetized when connected to the battery or just by being close to the permanent magnets.

3) Now connect the battery and rotate the armature a little if needed to get current to flow thru the armature winding.

4) Bring the second piece of Iron/Steel to one end of the bolt. It should be attracted much more strongly that the test in step 2), above.

If there is the same attraction from step 2) and from step 4) then either there is no current flowing thru the winding OR the winding is wound incorrectly; it should be all wound in the same direction; that is looking at the same end of the bolt, all the winding should be either clockwise or counter-clockwise.

Well, it's past my bedtime, hope this helps.

Have Fun!

Cheers,
Tom

p.s. Please keep us updated on yopur progress

 

[Ranveer]

Small update : I bought a 27 gauge wire, instead of the previous one which was around 32-34 gauge

Still didn't have time to make changes, I'll keep you guys posted.

 

[Ranveer]

The magnets are backwards. The N pole on one should be facing the S pole on the other one.

Without power applied, inspect the brush/armature alignment to make sure that both brushes never contact the same armature segment during a complete rotation.

By the way, a simple 2-pole motor like this will NOT start on its own! You will have to give it a good spin by hand to get it running.

The batteries are connected in series which means their voltages add but their current capability remains the same as one battery. I would expect this motor to require a rather high current to operate. I suggest the batteries be connected in parallel, all the "+" connected together and all the "-" connected together. The result will be 9V but with four times the current capability.

Better yet, take the advice of @tech99 in post #2 and use 2 to 4 "D" cells in series; they are more difficult to connect to though.
You might have to make a battery holder by nailing some metal strips to a piece of wood, then use rubber bands to hold the strips in contact with each battery. Much easier if you contact each battery individually, they won't stay in line if you place them head-to-tail as in a flashlight!

By the way, if you do not have a voltmeter to test the 9V batteries, here is a simple test. Using a single 9V battery, briefly touch the contacts to the top of your tongue just behind the tip.
a) If you sorta wish you hadn't done that, the battery is new
b) If you feel a substantial tingling and maybe a slight sour taste, it's "Usable"
c) Mild tingling, probably not much good for anything
d) No or very slight tingling, or an acid taste, dead

If the suggestions from everyone so far do not get it running, here is another simple test to help track down the problem.

1) Find a couple somethings, maybe screwdriver or plyers, made of Iron or Steel.
We want them NOT magnetized, so bring them in contact with each other then gently separate them. If they feel like they stick together then one or both of them are magnetized. Try other items from your tool box, or even some nails, until you find two Iron or Steel things that don't attract each other. They don't have to be the same shapes.

2) With no power to the motor, position the motor armature so the bolt is vertical, farthest away from the magnets. Now bring one of the Iron/Steel items to one end of the bolt. If it is attracted that means the armature is magnetized; remember how strong the attraction is, you will need it for comparison in the next step. Not to worry whether magnetized or not right now, it could have been magnetized when connected to the battery or just by being close to the permanent magnets.

3) Now connect the battery and rotate the armature a little if needed to get current to flow thru the armature winding.

4) Bring the second piece of Iron/Steel to one end of the bolt. It should be attracted much more strongly that the test in step 2), above.

If there is the same attraction from step 2) and from step 4) then either there is no current flowing thru the winding OR the winding is wound incorrectly; it should be all wound in the same direction; that is looking at the same end of the bolt, all the winding should be either clockwise or counter-clockwise.

Well, it's past my bedtime, hope this helps.

Have Fun!

Cheers,
Tom

p.s. Please keep us updated on your progress

First of all this helped me a lot, thank you.
Secondly I still regret putting those batteries near my mouth.

I have used a 27 gauge wire now istead of the earlier thinner one, there surely is magnetism in the bolt. It can freely hold a jumbo paper clip on both side, and there is slightly more magnetism on the second side.

I have yet to start it with a running start because the putty that I was using to hold everything in place came off.

I'll try and give it a running start and post about it tomorrow.

Thanks to everyone who has suggested, helped a lot.

 

[scottdave]

I realize this post is old, but a troubleshooting step should include checking the electromagnet. I am curious about the wire used for the coil. Could there be a break or worn place in the coating causing a short. The OP states it will hold a paper clip and one side is a little more than the other. This should really attract something like a paper clip when turned on.