Electric Motor Secrets

[LowTechIsCool]

winding coils

The mylar I am using to cover the stator poles works very well at preventing wear to the wire coating and is very thin, so I am reluctant to replace it with an epoxy coating, but I may have to. Im going to see how a glow gun holds to the mylar. The glue gun doesnt really bond strongly to the wire, but it may be enough to hold it in place, which is all I need at this point. I am not a fan of the glue gun because it comes out in relatively large globs, but I may be able to work around it.

On prewinding the coils:
I have a block that is the same size as the stator which I tried use to prewind. I found that I had trouble getting the coil off once I knocked it tight around the corners. Additionally, it was difficult to put the prewound coil onto the stator. I am ingnorant on this topic, so your advice is most appreciated

I use a tool I made to get the coils to hug tight around the corners. It is basicly 0.5x0.5x2 inch block with a 90 degree wedge cut out of one end. It has mylar on the wedge. I set the tool on the corner of the stator, where the wire is, and i tap the tool with a hammer. It makes the wire form a sharp angle, and doesnt harm the wire coating. This is partly why I have a hard time getting prewound coils off.

In the next week I will have a nice report on building the mechanical aspect of the motor, so that people will have a place to go for a summary of all the information that has accumulated on this forum and wont have to scan 30+ pages to get a single question answered. I hope this is in the spirit of the forum.

-Chris Corkum

[Jetijs]

A quick update.
I finished gluing the stator plates together. I used "Bison epoxy metal" for this. The epoxy is rather thick, so I had to dissolve it with some solvents, after that it is not as thick anymore and you can easily apply it on the plates using a paint brush. This works well. This epoxy is also dissolving in water when not cured, so I could easily wash off all the epoxy that squeezed out when the plates where pressed together with bolts. I used two endplates made out of 4mm thick iron to distribute the pressure evenly. The big hole on the inside is just 2mm bigger than the rotor diameter, this is because this way the lathe job guys wont be able to mess anything up as they did last time (separating plates) while making the inner surface smooth. Only after all the core machining is done eill the plates be removed, hopefully leaving a good stator core.



My rotor cores are also glued together ready for machining. Unfortunately I wont be able to progress until after holiday season, because all the machinists are already at holidays.
Thanks,
Jetijs

[LowTechIsCool]

Update

Hi,

Nice work on the stators, JetiJS. The outer diameter looks larger than before. I would be glad to hear about the changes you made.

I figured out my problems.

Done with finals and now I get to work on the motor. Machine shops close on Friday, so I get to see how much I can cram in till then.

-Chris Corkum

[Jetijs]

Hi Chris

This was my previous stator shape:


And this is the new one:


The main difference is that this design will allow me to use prewound cores. I calculated that with this design I should be able to use bifilar coils with 30 turns (50 turns total) of gauge 14 wire. Will see if I was right soon
The rotor plates are the same shape as in my previous motor.
Thanks,
Jetijs

[Necchi]

Hub motor?

Is it possible to swap the stator and rotor as in the drawing I've attached?

[Beshires1]

Is it possible to swap the stator and rotor as in the drawing I've attached?

I think so, But It wouldn't be nearly as efficient. Because of the windings moving around on the rotor, You would have to use some type of commutator to transfer the current from a stationary input to the spinning rotor coils (this usually means an energy lose due to sparking) A stationary coil as on the stator can be pulsed efficiently without these loses.

[broli]

I think so, But It wouldn't be nearly as efficient. Because of the windings moving around on the rotor, You would have to use some type of commutator to transfer the current from a stationary input to the spinning rotor coils (this usually means an energy lose due to sparking) A stationary coil as on the stator can be pulsed efficiently without these loses.

There are no rotational coils. According to his drawing there's only one stationary coil.

[Beshires1]

My Bad ... But if the outer is spinning around the stationary inner Coil then commutation will become difficult indeed. The rotor would have to be drum like , and have to support the entire rotor from one set of bearings. One end would have to be left open or have a bearing large enough to allow the stator wires to go through the bearings to the Stator. This could be done via a slot grooved in the stators stationary shaft. Now I think this motor will run but will have very little if any torque. And the larger the spinning drum the more so. Think of it this way, a fairly heavy wheel solidly attached to a axle is easier to stop from spinning by grabbing the outside of the wheel than to stop by grabbing the axle.

[Jetijs]

Is it possible to swap the stator and rotor as in the drawing I've attached?

If I understand correctly, in this case the rotor will acts as stator and the stator will act like rotor. The rotor will be stationary and the stator will rotate, right? If so, I don't see a reason why this should not work. I don't know about efficiencies and such, but it should work.

[Beshires1]

If I understand correctly, in this case the rotor will acts as stator and the stator will act like rotor. The rotor will be stationary and the stator will rotate, right? If so, I don't see a reason why this should not work. I don't know about efficiencies and such, but it should work.

Think about electric motor efficiencies like this. Jetis in your design, you want your bearings to rotate freely as possible, Less friction from the bearings translate to a smoother more efficient motor than a motor with the exact same setup windings, rotor size weight etc that has grease packed bearings that operate smoothly but the bearings have to churn threw the grease. The easier the motor can operate the less power consumed to do work. Ideally if you spin the rotating shaft, or drum by hand, It should spin freely for some time, gradually slowing down until it stops. As apposed to spinning by hand and it stops after only a round or two. Also any commutator source that produces sparks in the making or breaking of contacts will not be as efficient as one that doesn't produce sparks. Using a magnetic or reed switch as opposed to a micro switch (Lever) and cam design to time the rotor to the stator. AHH the list of things goes on and on....

[Jetijs]

Of course you are right about the bearings. What I meant with the efficiency was that I did not know if such a design as Necchi suggested was more efficient than the design I am currently working on. It would be a bigger load on bearings, but also there would be an increased flywheel effect.
As for bearings. As far as I know, the more precise the bearings are, the less backlash they have thus a little more friction. Of course, the smaller the friction the better, but in attraction motor we need the air gaps as small as we can make them, mine was 0.08mm And at those gap sizes, ordinary bearings might not be suitable and precision bearings should be used. This adds a little more drag but you don't really have a choice.

[Beshires1]

Jetijs,
Sorry, I misdirected my statement threw you. By the way, how many post will your rotor have?

[Jetijs]

What do you mean? How many poles? If yes, then my rotor will have just two poles, something like this:



Just the stator core will now have a bit different pole shape, like in pictures above

[Beshires1]

Its sorta weird, I know their normally referred to as poles, because they obviously will lack either a North Pole face or South Pole face, I didn't think you would understand me asking "How many Neutrals will your rotor have?" Or "Blobs of iron?" Protruding from the motor shaft. Any who, I figured you would know what I meant by Posts.

[Necchi]

Now I think this motor will run but will have very little if any torque. And the larger the spinning drum the more so. Think of it this way, a fairly heavy wheel solidly attached to a axle is easier to stop from spinning by grabbing the outside of the wheel than to stop by grabbing the axle.

I think what you said about torque was wrong. If the mechanical power originates at the gap, then surely the farther towards the rim of the bicycle the better? Both for torque and also to maximize the number of armatures - I should mention my diagram was simplified, in practice I would take a dead PM hub motor and work from there, so there would be more than four of them. (I think this is the term you were looking for in your last post btw - Armature (electrical engineering - Wikipedia, the free encyclopedia)).

What I'm worried about is how easily the magnetic current will follow the half-circle path around the drum.

Also I was going to follow up with a question about lighter weight materials. Remember my goal is to find some way of modifying a bicycle to at least get me up hills without dragging on flats, so I don't think iron is going to cut it. In a normal PM motor as shown at the bottom of this page...

go-hub electric bike conversion kits. USA DISTRIBUTER

...the rotor is just some permanent magnets so the weight isn't so much of a factor. If permanent magnets can be lightweight, I don't see why there shouldn't be some lightweight material that can take the place of soft iron or silicon steel. I'm looking into ferrite ceramics at the moment.