panandtilts
1 µW
So to start off, I'm a mechanical engineer and anything electrical is not my forte. I've been researching through this forum and rcgroups in the motor subforum there the past few weeks trying to soak up as much knowledge as possible, but a lot of it is still very fuzzy.
I'll try to keep this short.
What I'm trying to do: Design a BLDC motor for a ceiling fan I'm designing. Doesn't seem very exciting, but I believe it's a great stepping stone in designing motors, controllers, and rotor blades. I'll be designing everything from the ground up, this includes the rotor geometry (a bunch of excel and some CFD) to optimize the geometry, then designing a motor to run this said fan.
Current State: Almost done designing the rotor, but have not finalized anything, therefore do not have any torque requirements yet (kind of important for designing a motor huh?)
Past experience: The most relevant experience would be designing the motor housing/rim for the CSIRO (now Marund) motor for a solar car.
Motor specifications: As stated before, the torque requirements have not been settled yet so it's hard to say, but it will only be spinning at 30-150rpm. So basically a very low Kv + high torque motor. Would also like to design it as efficient as possible
Moving to the questions. So I haven't fully decided between a radial flux or axial flux design, but am leaning more towards a coreless axial flux design due to the fact I don't want to cut custom laminations for the stator.
Copper fill: higher the better as it'll be a stronger electromagnet and will be more efficient
Winds: Using the BLDC equation, more winds obviously equals higher torque but with the trade off of higher resistance
1) Litz wire: Would litz wire be needed due to the fact it will be used at such a low rpm? I understand it's usually necessary especially for coreless stators due to the reduction of eddy currents, however I understand it's more beneficial for higher frequency motors.
2) Poles: More poles the higher the torque, what do you recommend as a starting point?
3)Should I be trying to maximize my voltage and minimizing current for more torque and less current losses?
4) For a coreless dual rotor, single stator design, the stator width is important due to the fact it counts in the air gap, so I should try to minimize this as much as possible while making sure I have enough space for the number of windings I need correct?
5) If I want to use round magnets, the higher the pole count, the smaller the magnets I can use for a given diameter, is there any major disadvantages of this I should know?
6) In this thread: http://endless-sphere.com/forums/viewtopic.php?f=30&t=14339&start=75 , It talks about different winding styles and it mentions staggered and overlapping windings, however I haven't seen any of this in any of the builds here, is there a reason? What looks promising is the staggered winding with two layers of coils, overlapping by 50%. This will however allow me to get a lot more coils relative to magnets, is there a downside to this? I understand you want a close to 1:1 ratio of poles to minimize cogging which should be important with a low rpm motor.
7) In the same thread as #6, they state that you want the ID of the coils to be the OD of the magnets, so that the coil can capture the flux of the magnets through it's full number of turns. I don't understand what this means, could someone explain? Also if say I make the coil a trapezoid or ellipse, does this still apply? (as in I should be able to fit the magnet inside of the trapezoid or ellipse)
8 ) Since the round magnets will basically form a ring, I would only need backing plate in the shape of a ring as well correct? How much bigger should the backing plate be relative to the magnets then? As in how much more should I extend radially (radius).
This is what I have right now but I'm sure I'll have much more to come, sorry if it's very scattered as I think maybe I'll looking too much into everything and my thoughts are just jumbled. Thanks!
I'll try to keep this short.
What I'm trying to do: Design a BLDC motor for a ceiling fan I'm designing. Doesn't seem very exciting, but I believe it's a great stepping stone in designing motors, controllers, and rotor blades. I'll be designing everything from the ground up, this includes the rotor geometry (a bunch of excel and some CFD) to optimize the geometry, then designing a motor to run this said fan.
Current State: Almost done designing the rotor, but have not finalized anything, therefore do not have any torque requirements yet (kind of important for designing a motor huh?)
Past experience: The most relevant experience would be designing the motor housing/rim for the CSIRO (now Marund) motor for a solar car.
Motor specifications: As stated before, the torque requirements have not been settled yet so it's hard to say, but it will only be spinning at 30-150rpm. So basically a very low Kv + high torque motor. Would also like to design it as efficient as possible
Moving to the questions. So I haven't fully decided between a radial flux or axial flux design, but am leaning more towards a coreless axial flux design due to the fact I don't want to cut custom laminations for the stator.
Copper fill: higher the better as it'll be a stronger electromagnet and will be more efficient
Winds: Using the BLDC equation, more winds obviously equals higher torque but with the trade off of higher resistance
1) Litz wire: Would litz wire be needed due to the fact it will be used at such a low rpm? I understand it's usually necessary especially for coreless stators due to the reduction of eddy currents, however I understand it's more beneficial for higher frequency motors.
2) Poles: More poles the higher the torque, what do you recommend as a starting point?
3)Should I be trying to maximize my voltage and minimizing current for more torque and less current losses?
4) For a coreless dual rotor, single stator design, the stator width is important due to the fact it counts in the air gap, so I should try to minimize this as much as possible while making sure I have enough space for the number of windings I need correct?
5) If I want to use round magnets, the higher the pole count, the smaller the magnets I can use for a given diameter, is there any major disadvantages of this I should know?
6) In this thread: http://endless-sphere.com/forums/viewtopic.php?f=30&t=14339&start=75 , It talks about different winding styles and it mentions staggered and overlapping windings, however I haven't seen any of this in any of the builds here, is there a reason? What looks promising is the staggered winding with two layers of coils, overlapping by 50%. This will however allow me to get a lot more coils relative to magnets, is there a downside to this? I understand you want a close to 1:1 ratio of poles to minimize cogging which should be important with a low rpm motor.
7) In the same thread as #6, they state that you want the ID of the coils to be the OD of the magnets, so that the coil can capture the flux of the magnets through it's full number of turns. I don't understand what this means, could someone explain? Also if say I make the coil a trapezoid or ellipse, does this still apply? (as in I should be able to fit the magnet inside of the trapezoid or ellipse)
8 ) Since the round magnets will basically form a ring, I would only need backing plate in the shape of a ring as well correct? How much bigger should the backing plate be relative to the magnets then? As in how much more should I extend radially (radius).
This is what I have right now but I'm sure I'll have much more to come, sorry if it's very scattered as I think maybe I'll looking too much into everything and my thoughts are just jumbled. Thanks!
If the fan had been very fast or high-torque, it's possible it could've done a lot more damage depending on the rest of the circumstances. 
