But the number of cogging steps per revolution won't directly affect the total parasitic torque (and therefore efficiency)? Right?rhitee05 wrote:But, going over to the topic of Thud's thread, the calculator shows that 16p has 144 cogging steps while 20p has 180, so 20p will probably have somewhat lesser cogging force.
At some stage, I thought it might be interesting to try round magnets, in order to get a more sinusoidal BEMF.rhitee05 wrote:Assuming trapezoidal BEMF. The definition is slightly different for a sinusoidal motor, although I'm pretty sure this design will end up with a more trapezoidal BEMF.
I certainly didn't intend to imply that.bearing wrote:I believe it was stated earlier in this thread that this design wouldn't have any end turn losses. Is that true?
Yes, in this case, only when the coils are running radially will they contribute to torque. If you have a wedge shape inner core (mine is uniform), you can take advantage of wedge shaped magnets but the proportion of the coils which is non-contributory will increase significantly. It would be interesting to do the comparison.bearing wrote:In a normal radial "outrunner" design, only the part of the windings that are parallel to the magnets will contribute to torque, correct? won't the same apply to this design?
Miles wrote:But the number of cogging steps per revolution won't directly affect the total parasitic torque (and therefore efficiency)? Right?
Miles wrote:At some stage, I thought it might be interesting to try round magnets, in order to get a more sinusoidal BEMF.
Miles wrote:Deciding the ratio of iron to copper:
If the goal is to maximise the continuous torque output, the amount of iron only needs to be sufficient to avoid saturation up to that specific torque level. By reducing the amount of iron and so being able increase the amount of copper, you decrease both parasitic and direct losses and raise the maximum sustainable torque level by sacrificing the peak levels of torque.
Miles wrote:I've saved it as an A'CAD 14 DXF
Magnets to be N48
Air gap circa 0.7 mm
Allowing for insulation, copper fill ratio is 0.75 of marked area.
Possibly 2 x 6 turn coils (12t) ? This gives slightly under 0.5mm thick strip.
Magnet flux backing 2mm thick steel.
Miles wrote:I discovered that the mid radius section I did yesterday was off centre by 0.6mm. Should I redo it?
When it's consistent with the other 2 sections I've just done, it will be 35.5mm.rhitee05 wrote:What's the radius for that center section? By my math, I put it at about 36.4 mm.
rhitee05 wrote:Still, the shape of the phase B waveform looks promising. Correcting the units, I get a Kv of about 174 RPM/V for this geometry. Is that ballpark of what you're trying for? Caveat: this simulation uses N40 magnets, because FEMM doesn't have a built-in model for N42 or N48, so the Kv will end up being lower for either of those strengths.
Miles wrote:Crikey! I didn't expect to get that close! I was aiming for 150 Kv with N48 magnets
That's with 12t? Right?
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