Hello all,
I was wondering if its possible to develop a hub motor design with separately excited windings for both stator and rotors (i.e. No use of Magnets). I am exploring this idea for the use in rotation systems where free wheeling can occur when not powered.

What do you think? Is it possible? or are there any other solutions to this? (apart from freewheel clutches)

 

Welcome to AAC!
Motors with both field and rotor coils are well-known. See, for example, this article.

 

What do you think? Is it possible? or are there any other solutions to this? (apart from freewheel clutches)

What do you have against free wheel clutches? The problem with separately excited rotor ans stator in a hub type motor is the need for them to be narrow instead of wide, to get enough power out to do the moving.

If your interested in something that will work in that situation, thin and no magnets, except windings on a stator, you should look at SRM(Switched Reluctance Motors). It's one of the earliest electric motors developed, but wasn't widely know until recent times. Now that there are solid state switching devices it is in much wider use today. https://en.wikipedia.org/wiki/Switched_reluctance_motor

There is much literature available out there about them and their drives too.
https://www.google.com/search?client=firefox-b-1-d&q=Switched+Reluctance+Motors

 

What do you have against free wheel clutches? The problem with separately excited rotor and stator in a hub type motor is the need for them to be narrow instead of wide, to get enough power out to do the moving.

Can you elaborate on this for me please? Do you have any links that I can look through in depth?

Thanks Alec, I am well versed with the standard wound field configurations - series, shunt and Compound, What I am interested is in the application of separately excited windings in the Hub style motors - Outer rotors and inner stators and I cant really find much on this :-\

 

Can you elaborate on this for me please? Do you have any links that I can look through in depth?

Thanks Alec, I am well versed with the standard wound field configurations - series, shunt and Compound, What I am interested is in the application of separately excited windings in the Hub style motors - Outer rotors and inner stators and I cant really find much on this :-\

Why do you think most every hub motor is a BLDC type? They allow concentrated power from a narrow package. Then when both motor elements are energized you also need brushes of some sort. The reason you can't find any information is no one is doing it, or at least no one that is serious about it and understands motors. The SRM does it with no magnets like you asked for.

 

Why do you think most every hub motor is a BLDC type? They allow concentrated power from a narrow package. Then when both motor elements are energized you also need brushes of some sort. The reason you can't find any information is no one is doing it, or at least no one that is serious about it and understands motors. The SRM does it with no magnets like you asked for.

Thanks Shortbus, I will look into SRM, I am not particular about eliminating brushes, My main idea is to eliminate cogging torque and on cursory glance, SRM seems to have torque ripple at low speeds, my motor will start from 0 rpm and may go upto 1200 rpm and will require a sufficiently large torque to carry a load of 150-200 kgs from speeds of 0 to 60 kmph. So the low speed performance is needed.

 

It should be possible to eliminate "Cogging torque" without resorting to wound field technology. For starters, none of the ironless rotor motor types have any cogging torque, nor do most induction motors. Replacing magnets with coils certainly reduces efficiency a fair amount. What is the intended purpose of such a motor, anyway? What specific benefit are you seeking?

 

It should be possible to eliminate "Cogging torque" without resorting to wound field technology. For starters, none of the ironless rotor motor types have any cogging torque, nor do most induction motors. Replacing magnets with coils certainly reduces efficiency a fair amount. What is the intended purpose of such a motor, anyway? What specific benefit are you seeking?

I am working towards a hub type motor to be used on e-bike or mopeds, Induction motors are out of the list as there wouldnt be enough cross section to get a decent enough of torque out of it,
Specific benefit - I need the wheel to rotate freely when the electrical power is exhausted or not in use.

 

OK, for an E-Bike it is an interesting application, and one that would not tolerate the power wasted in a wound-field motor. Skewed rotor slots have been used to reduce the gogging effect for many years and are fairly well understood by motor designers. And if there is any apparent cogging effect I suggest that it is caused by the driver circuit somehow allowing current to flow while the drive is not powered but the wheel is rotating. That is, a poorly designed driver circuit.

 

Skewed rotor slots have been used to reduce the gogging effect for many years

It should be possible to eliminate "Cogging torque" without resorting to wound field technology. For starters, none of the ironless rotor motor types have any cogging torque,

Yet another one you know little about but have to comment on?

 

I need the wheel to rotate freely when the electrical power is exhausted or not in use.

I'm pretty sure you are overstating the cogging effect in a hub motor. The difference in diameter of the hub over the wheel would or should make it negligible. If it wasn't, there wouldn't be so many hub motors out there in the market.

Hub motors were even being talked about and developed a few years ago for use in cars and trucks. The SRM motors are used a lot today in deep mine machines to drive the wheels and hydraulics.

 

Yet another one you know little about but have to comment on?

NONE of the ironless motors that I have used or worked with had any cogging torque that I could detect.

 

NONE of the ironless motors that I have used or worked with had any cogging torque that I could detect.

How big can these get? It seems a heavy load can cause the motor to heat up and burn up the wiring. They are better for applications where the loads are pretty much unvarying.

 

NONE of the ironless motors that I have used or worked with had any cogging torque that I could detect.

Are you referring to P.M. field?
If so cogging is prevalent especially when run in BLDC mode and where motion feedback is absent.
Max.

 

Are you referring to P.M. field?
If so cogging is prevalent especially when run in BLDC mode and where motion feedback is absent.
Max.

Max, what the TS is wanting to prevent is cogging while the motor is not energized. Apparently this is a complaint on a hub-motor variety of electric bicycle. At least that is the concept that I got from the TS post. I have tried out two different electric bikes and did not notice any such cogging effect, but I also found the claims of the sales person totally non-believable.

 

NONE of the ironless motors that I have used or worked with had any cogging torque that I could detect.

And none of them are big enough or even recommended for the application at hand, Which like the other thread doesn't seem to bother you at all.

 

Why is this cogging something you need to design around? How much cogging do you think comes from a single cylinder 4stroke engine like would normally be employed? That's one cog/pulse per every two revs, surely more perceptible "cogging" than would be felt by a BLDC with some multiple of 3 cogs/pulses per rev? And yet nobody complains of this? Is it really a problem? Seems to me at most it would feel like a slight vibration below walking speed.

 

than would be felt by a BLDC with some multiple of 3 cogs/pulses per rev?

Cogging count on a BLDC is an even number.
i.e. pole pairs, the minimum of course is 2 up to max of 8 usually.
Max.

 

And keep in mind that the TS is wanting to prevent the cogging with a NON-POWERED motor. Looking again at the initial post, it is not clear just what the application would actually be. Post #8 indicates that it actually is a bike of some form.

 

Cogging count on a BLDC is an even number.
i.e. pole pairs, the minimum of course is 2 up to max of 8 usually.
Max.

DOH! You're right.