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 which motor?

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rjw
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PostSubject: which motor?   Tue May 28, 2013 10:28 pm

Check out these motors...the one on the left is not what I am used to seeing in a brushed can motor


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Don Doerfler
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PostSubject: Re: which motor?   Wed May 29, 2013 10:35 am

hmmm would you think that would reduce cracking
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rjw
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PostSubject: Re: which motor?   Wed May 29, 2013 3:45 pm

I realize that the one on the left is less likely to have the magnet unglue, but what the f am I looking at and how does it compare to the normal run of the mill perm mag motor...In testing so far, the kn is a bit low, but it seems to have planty of power???
Anyone seen this before? and if so, what 's the deal?

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PostSubject: Re: which motor?   Wed May 29, 2013 8:38 pm

I'm guessing that it's cheaper to make that way, but it sacrifices absolute power and reduces airflow. The windings and rotor look like they're a bit rougher as well, which makes me think it's a cost thing.
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rjw
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PostSubject: Re: which motor?   Wed May 29, 2013 10:05 pm

MikeNCR wrote:
I'm guessing that it's cheaper to make that way, but it sacrifices absolute power and reduces airflow. The windings and rotor look like they're a bit rougher as well, which makes me think it's a cost thing.

Initial testing showed that the power output of the wierd motor was excellent. That along with the single round magnet would make possibly a decent choice. It also ran fine from 7.2 to 14.4 volts. I am working on a version with true brushes, which if it happens, it could be the cat's meow in motors for 3 pounders.
The design is more of an electromechanical deal...there is little to no actual magnetic attraction at all.
If I put bot motors in a bin of steel screws, the pm motor would have many stuck to it, while the other would have none.
Still need to do in bot extensive testing, but so far I like it...On a side note, no metal filings stick to it....lol

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PostSubject: Re: which motor?   Wed May 29, 2013 10:38 pm

rjw wrote:
MikeNCR wrote:
I'm guessing that it's cheaper to make that way, but it sacrifices absolute power and reduces airflow. The windings and rotor look like they're a bit rougher as well, which makes me think it's a cost thing.

Initial testing showed that the power output of the wierd motor was excellent. That along with the single round magnet would make possibly a decent choice. It also ran fine from 7.2 to 14.4 volts. I am working on a version with true brushes, which if it happens, it could be the cat's meow in motors for 3 pounders.
The design is more of an electromechanical deal...there is little to no actual magnetic attraction at all.
If I put bot motors in a bin of steel screws, the pm motor would have many stuck to it, while the other would have none.
Still need to do in bot extensive testing, but so far I like it...On a side note, no metal filings stick to it....lol

I'd be curious to see real world torque/rpm from both motors. The description of the magnetism makes me think that in some way the full-round magnet should be weaker.

Quote :

Magnetic field strength is directly proportional to the torque constant, Kt. So as magnetic field strength is increased or decreased, the torque, τ, will increase or decrease proportionally. Which makes sense because the stronger the magnetic field, the stronger the "push" on the armature.

Magnetic field strength is also directly proportional to the voltage constant, Ke. However Ke is inversely proportional to the angular velocity:

ω=VKe
So, as the magnetic field increases, the speed will decrease. This again makes sense because the stronger the magnetic field, the stronger the "push" on the armature so it will resist a change in speed.

Because power out is equal to torque times angular velocity, and power in equals power out (again, assuming 100% efficiency), we get:

Pin=τ⋅ω
So any change to torque or speed will be directly proportional to the power required to drive the motor.
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rjw
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PostSubject: Re: which motor?   Thu May 30, 2013 1:10 am

I agree.....but there are other factors as well

1) the much larger rotor, once spinning, would be more likely to stay spinning, wouldn't you say?

2) The full circle magnet would be better in a combat robot, simply because it wouldn't have a tendency to come loose

I am not by any means defending this motor, but it has some interesting characteristics, not to mention that it must be working on a slightly different principal. There is absolutely almost zero magnetism!!
I spoke to an electrical engineer about it and he suspects that the motor operates differentely from our normal pm motor.
I am just trying to educate myself, in that I've never seen this in a brushed motor. I have in brushless cdrom motors, etc. that had this type of full circle magnet, fwiw

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