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Hub motor with separately excited rotor and stator configuration

Quintos007

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Hello all,
Not sure if this is the right thread chain, But 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.

I am aware of series, shunt and compound configurations and observed that it may not serve my purpose.

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

schmitt trigger

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It could be done, but then it wouldn’t be a brushless motor, as an electrical current would have to be fed to the rotor.

Additionally, the field current would cause an efficiency loss.

For that reason, I doubt you’ll find commercially available products.

Now that I’ve your attention; I am in the process of purchasing an E-bike myself. Some people complain what you mentioned, that the permanent magnets cause some cogging torque such that it prevents complete freewheeling.
Is that an issue? What is your experience?
 

fourtytwo

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I don't know if it's any help but I used to have a 600W wind turbine and it had almost no noticeable cogging torque, guess its down to the number of poles (and possibly the super large gap!), see enclosed picture (laptop cord for scale).
Ohh I almost forgot, cogging torque can also be reduced by skewing the poles as found for example in high quality servo motors.

P1130480.jpg
 
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schmitt trigger

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Thanks, as you correctly mentioned, it all depends on the motor design and the application.

That is the reason I asked the OP if he had experienced cogging torque in an e-bike.
But this was his first and only post so far, so very likely I might not obtain a reply.

- - - Updated - - -
 

Quintos007

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Thanks, as you correctly mentioned, it all depends on the motor design and the application.

That is the reason I asked the OP if he had experienced cogging torque in an e-bike.
But this was his first and only post so far, so very likely I might not obtain a reply.

- - - Updated - - -
Hi Schmitt,
Yes, as you correctly deduced, I am looking to eliminate cogging torque also the fact that when the motor is not powered, it acts as a generator in the presence of the permanent magnet which inturn sucks the energy out of the system.
I am looking to completely remove this and have a full free wheeling effect.
 

KlausST

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Hi,

Even if you calculate 50A continuous current, that's only going to be 0.25W of power
What about using an asynchronous 3 phase AC motor. There is no permanent magnet.

You say it acts like a generator...so to reduce torque the first thing would be to prevent current flow.

Klaus
 

Quintos007

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Hi,


What about using an asynchronous 3 phase AC motor. There is no permanent magnet.

You say it acts like a generator...so to reduce torque the first thing would be to prevent current flow.

Klaus
Hi Klaus,
As Schmitt deduced, this is for an e-bike / moped, so, I will not have the necessary cross section area to get a decent torque from a 3 Phase AC Motor, hence I took it out of the list.
The size to be implemented is of a 11" Hub motor dimension.
 

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