Spin right round motor

[casady961]

Hi
My son age 14, put together the motor with all the coils. He gets a reading with the voltmeter and set up is correct based on picture sent to me by Amy. THe coils do not spin at all. The battery is good. Please let me know how to rectify this problem.

Thanks so much

[rmarz]

casady961 - Sorry you are experiencing some difficulties. Amy reached out to a few experts tonight to try to help. The good news! I built this motor this evening in the garage and it does, indeed, spin. In the process of building it I found a few critical issues that may be part of your problem.

1) The removal of the insulation on only half of the wire on each end is critical. It must also be symmetric, that is identical on both leads. The diagram actually shows it pretty well. When you are looking at bare copper on one side, you should be seeing the bare copper on the other side. The motor depends on this to 'commutate' the current to the motor. That means it alternately turns the coil on and off once in every revolution. If all the insulation were removed on the leads, the coil would always be on and just align to the magnet and not move.

2) Try to balance the coil as carefully as possible so that it will spin easily and not have a 'heavy spot' somewhere in it's rotation. That will assure the best rotation and speed.

3) The position of the magnet is critical because the magnetic field generated by the coil when it is energized must by synchronized to the position of the magnet. I found that in my first attempt with the magnet directly under the coil I would get attraction, but no rotation. When I changed the position of the magnet to the side (about 30 degrees) the motor started to spin. Also, place the magnet as close to the coil as you can without touching it.

I made a short movie of the crude motor and will try to find a way to share it with you. Good luck.

Rick Marz

[rmarz]

casady961 - Here is the link to the video.

Rick Marz

http://youtu.be/5T5Nfi6N96Q

[casady961]

Ok, I see your video. A few questions, you mention 2 d cells, it came with only one d cell holder. also, you mention stripping the wire, which wire is that because we have no wire that you can strip bc none of it is insulated. So is it possible that we recieved the wrong wire? We have a roll of magnet wire and copper wire, nothing with insulation in the kit.

thanks so much

[rmarz]

casady961 - Sorry you are still having difficulties. Here are some things to narrow down your debugging.

1) I have verified that the coil does spin with a single, fresh 'D' cell.

2) I think your problem is in creating the commutating capability (the ability of the coil to conduct for only half of the rotation) on the extended coil leads This is the 'shaft' that is created by the ends of the coil wire. This is critical. You seem to be having difficulty determining where the insulation is on the coil, or even if you have insulated wire. Magnet wire is copper wire with a very thin coating of varnish that is an insulator, it does not have a plastic insulation in the sense that it is similar to what you would see on doorbell or telephone wire. Typically it is a transparent reddish-brown or possibly green color varnish. It is so thin that you can see through it. Your coil must be wound of magnet wire with this thin varnish insulation, never non-insulated copper wire. If non-insulated copper wire were used the many turns of the coil would be shorted out and you would not have a coil capable of producing much of a magnetic field. I don't know what was included in the kit, but test the magnet wire by scraping a small bit off an end with a sharp knife. You should see the color of bare copper exposed. The insulated magnet wire is used to wind the coil with the two ends of the wire sticking out to become the shaft that rotates. The two ends of the coil are the leads that must have only half of the insulation removed. This is well described and shown in the experiment details.

3) When you are sure that you have followed these steps carefully, I mentioned that magnet placement is very critical. In my case, I had scraped the insulation off the top half of the leads/shaft when the coil was oriented vertically. This seems to be exactly as depicted in the drawing, but in practice I had to move the magnet about 90 degrees from what was shown in the diagram. In my situation, the magnet had to be placed at the 9 o'clock position relative to the shaft, not at the 6 o'clock position directly below the coil as shown.

Let us know if this helps and if you have resolved the 'magnet wire' insulation issue.

Rick Marz

[casady961]

Hi, I was just wondering what the results are suppossed to be. Is the larger coils (50) supposed to spin faster than the 10 coils or vice versa? Thanks so much

[deleted-71882]

Hello casady961,

Your question about which should turn faster, the ten turn motor or the fifty turn motor, is often asked. The answer is complicated, so I'll try to discuss it a bit to help you and other experimenters.

This simple type of motor has several factors that affect how fast it spins: the number of turns, the strength of the magnet and its closeness to the coil, the resistance of the coil, the precision of the contacts at each end, the friction of the spinning wire on the supports, the type and freshness of the battery. I'm sure there are other less significant factors, but I will discuss the ones above.

1. Suppose the coil supports are perfect--no friction, and the coil has no electrical resistance. Two opposing effects occur together when current is passed through the coil and it begins to turn.
   The first effect is that the current through the coil creates a magnetic field, and this field pulls and pushes on the permanent magnet just as two permanent magnets push on each other. This force causes the coil to begin to turn. If the enamel was scraped off at an angle such that the coil is turned, it will continue to turn until the enameled portion of the wire contacts the support, and the current stops. The inertia of the coil causes it to continue to turn until the scraped part of the wire contacts again and more force is applied to the coil. The speed will just increase without limit.
   The second effect is that when the coil turns in the field from the permanent magnet, an electric potential is generated that opposes the current caused by the battery. As the coil spins faster, the induced potential increases until it equals the battery potential, then no current flows, but the coil continues to turn because we stipulated here that the support was frictionless.
   The potential induced by spinning also depends on the number of turns in the coil. The potential is, in fact, proportional to the number of turns. Therefore the coil with more turns can reach the induced potential to match the battery while spinning slower. The rate at which it would spin is inversely proportional to the number of turns; the 10 turn coil should spin five times as fast as the 50 turn coil.
   I'll bet your motor doesn't perform that way. Why?
2. A real-world motor will not be frictionless. Let's now suppose that the friction of the coils on the support is the prime factor. At rest, a larger magnetic field is generated when the coil has more turns: the field is proportional to the number of turns. The larger field interacts with the field of the permanent magnet to give a force proportional to their product. Thus a coil with more turns will be accelerated faster by the greater force. The frictional force will increase proportionally to the speed of rotation. The coil will accelerate until the magnetic force matches the frictional force. A coil with more turns will spin faster than one with fewer turns. This is the answer given in the FAQ for this project, and it is correct for many motors that are constructed. Air resistance , vibration, and other imperfections will also act to slow the motor down just as friction does.
3. Given these two opposing effects (1) and (2), your motor will spin at a speed somewhere in between the two limits. You can try using rough supports to increase friction or devise methods to decrease it and see what effect you can have on the rotational speed.
4. As you wind more turns on the coil, the electrical resistance increases a bit, so less current flows, and you will never see the ideal case (2). In practical cases, the battery resistance may be larger than the coil resistance, so this effect is probably small.
5. A stronger magnet also has two opposing effects in conjunction with effects (1) and (2). A stronger permanent magnet produces a stronger force on the coil to push it faster, but a stronger permanent magnet also induces a stronger reverse potential and causes the maximum speed to decrease. The closer the permanent magnet is to the coil, the stronger its field at the coil.
6. A fresh battery has a lower internal resistance than a used one, so it can supply more current to the coil to overcome friction.

So the rotational speed of your motor doesn't depend on the number of turns in a simple, one-effect way. Perhaps you can examine the number of turns and some of the other factors I mention here to sort out the relative importance of each effect.

Good luck, WW