What are the reluctance values for this DC Motor?

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SUMMARY

The discussion centers on calculating the reluctance values for a DC motor, specifically addressing the rotor and its relationship to the stator and air gaps. Participants emphasize the importance of using the formula R = l/μ*A for reluctance calculations, where 'l' is the length, 'μ' is the permeability, and 'A' is the area. The rotor's diameter is noted as 4 cm, and it is suggested that it may be approximated as a cube for simplification. The conversation highlights the complexity introduced by the cylindrical rotor and the necessity of considering material properties when calculating total reluctance.

PREREQUISITES
  • Understanding of magnetic circuits and reluctance
  • Familiarity with the formula R = l/μ*A for reluctance calculations
  • Basic knowledge of Finite Element Analysis (FEA)
  • Concept of permeability in magnetic materials
NEXT STEPS
  • Research how to apply Finite Element Analysis (FEA) for magnetic circuits
  • Learn about the properties of different rotor materials and their impact on reluctance
  • Study the effects of approximating cylindrical shapes in magnetic calculations
  • Explore advanced reluctance calculation techniques for complex geometries
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Electrical engineers, students studying electromagnetism, and professionals involved in motor design and analysis will benefit from this discussion.

TheRedDevil18
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Homework Statement


motor.PNG


Homework Equations

The Attempt at a Solution



I know from a basic magnetic circuit that their will be an Rcore and an Rairgap but what about the rotor in the middle ?
 
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TheRedDevil18 said:

Homework Statement


View attachment 96183

Homework Equations

The Attempt at a Solution



I know from a basic magnetic circuit that their will be an Rcore and an Rairgap but what about the rotor in the middle ?
Wow, that looks pretty non-trivial. Are you supposed to use Finite Element Analysis to come up with the answer? If it were just flat air gaps, that you should be able to calculate. But having that cylindrical piece and round air gaps makes this very complicated, IMO.
 
And BTW, your title calls this a motor. Is the cylindrical piece in the middle magnetized?
 
berkeman said:
And BTW, your title calls this a motor. Is the cylindrical piece in the middle magnetized?

The cylindrical piece in the middle is the rotor and the core is the stator. They said assume that the area of each air gap is 18 cm^2
 
TheRedDevil18 said:
The cylindrical piece in the middle is the rotor and the core is the stator. They said assume that the area of each air gap is 18 cm^2
Oh, so approximate it as two flat air gaps? That simplifies things a lot. What equations do you use to calculate the reluctance of the different magnetic path sections?
 
berkeman said:
Oh, so approximate it as two flat air gaps? That simplifies things a lot. What equations do you use to calculate the reluctance of the different magnetic path sections?

R = l/u*A

I know how to calculate the reluctance for the core and the air gap but I'm not too sure about the rotor part. Is their supposed to be a reluctance for the rotor ?
 
TheRedDevil18 said:
Is their supposed to be a reluctance for the rotor ?
Yes, but it would be good to see how they ask the question. Are you given a different μ for the rotor material? Or are you supposed to assume the same μ as the armature? If they say you can approximate the air gaps as flat, do they say you can approximate the cylindrical rotor as a cube?
 
berkeman said:
Yes, but it would be good to see how they ask the question. Are you given a different μ for the rotor material? Or are you supposed to assume the same μ as the armature? If they say you can approximate the air gaps as flat, do they say you can approximate the cylindrical rotor as a cube?

They don't say anything about the rotors material so I think it's the same as the core. They do give the diameter of the rotor core to be 4 cm. I think it has to be approximated as a cube
 
Typically, the reluctance of metal is so much smaller than that of the air gaps that one would just use the air gap reluctances to determine the total reluctance. However, since you're given all those dimensions I guess you're not supposed to do that. I hope they gave you the permeability of the metal ... then as berkeman says you have a bigger job determining the effective path areas.
BTW you never posed the question in the first place ...
 

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