F4P's 144mm low rpm Outrunner

yes. 6.8mm for 48p and 7.5mm for 42p. it's the same percentage coverage and optimized for minimum torque ripple.
 
You've increased the magnet area so, if the cross-sectional area of the tooth remains the same, the flux density at that point will increase. That certainly accounts for the major part of the difference.
 
Thanks for the explanation, Miles! I figured it out on the bike this morning. I haven't increased the overall magnet area, but the partial area, that a single magnet covers the tooth stem. I assume this effect is linked with the winding factor.
6.8mm magnet width for both configurations gives the same flux density. So overall i have only 87,5% magnet area and the same flux and torque. ...but torque ripple is aweful now, it doesn't seem to be possible to compare configuration with the exact geometric stator copy.
 
Yes. If the magnet width is less than the tooth head width, the peak flux density relationship is largely between the magnet area and the tooth cross sectional area. The percentage of the pole covered by the magnet isn't directly relevant. But, of course, it is relevant to the level of torque ripple...
 
F4P said:
So overall i have only 87,5% magnet area and the same flux and torque. ...but torque ripple is aweful now,
Click to expand...
Try around 75% to 80% pole coverage. Also, try adjusting the slot opening width. This often goes the opposite way to what you might expect. Sometimes, widening the slot opening will reduce torque ripple.
 
Miles said:
F4P said:
So overall i have only 87,5% magnet area and the same flux and torque. ...but torque ripple is aweful now,
Click to expand...
Try around 75% to 80% pole coverage. Also, try adjusting the slot opening width. This often goes the opposite way to what you might expect. Sometimes, widening the slot opening will reduce torque ripple.
Click to expand...

the 87,5% was meant in relationship 42p to 48p

thanks for all the input.
 
Has someone a idea how to scale up my 42pole36slot motor concept to a outer radius of 400mm? I like the idea to have the outer rotor rim mounted.

I have to keep the open circuit iron losses below 15W.
 
F4P- Miles is offering you sage-level advice for improving your motor design.

You will find it's effortless to make the torque, it's simply a matter of making a big radius and adequate width, there is no skill required to simply design a motor that has good torque/power potential.

Miles is trying to show you what makes a good motor from another POS motor design. It's in the BEMF waveform being sinus, and hence the minimization of harmonic content and torque ripple as a result.

It is already a well proven technique to take a big radius stator and make the torque/power you want. If you wish to also make your motor design efficient and controllable and smooth and low-parasitic harmonics etc, I advise you directly follow any advice Miles so kindly takes the time to offer you.
 
liveforphysics said:
F4P- Miles is offering you sage-level advice for improving your motor design.

You will find it's effortless to make the torque, it's simply a matter of making a big radius and adequate width, there is no skill required to simply design a motor that has good torque/power potential.

Miles is trying to show you what makes a good motor from another POS motor design. It's in the BEMF waveform being sinus, and hence the minimization of harmonic content and torque ripple as a result.

It is already a well proven technique to take a big radius stator and make the torque/power you want. If you wish to also make your motor design efficient and controllable and smooth and low-parasitic harmonics etc, I advise you directly follow any advice Miles so kindly takes the time to offer you.
Click to expand...

Thanks for your post, Liveforphysics!

I'm following miles advices carefully. I've been reading every motor building thread. At the moment http://endless-sphere.com/forums/viewtopic.php?f=30&t=57371 is very active an the idea of the big air gab area is not bad. I have some nice mechanical concept for a 20" rim with integrated outer rotor. But my application is not the typical ebike use case. i need up to 1000rpm direct drive and very low iron losses. So pole number is limited...
200 Watt count output is more than enough.
 
For the stator i have a carbon fiber structure in mind, that looks cross sectional like a diabolo from the center to the inner stator radius. Should be ridged and lightweight.
 
What is the trade off with very low electric rpms (for the controller)? I'm struggeling with the iron losses at cruise speed and thinking of reducing the number of pole pairs. Iron losses make 90% of the losses because of the low power output demand at 700rpm and 100Watts...

At the moment I'm covering 0 - 100kph with 0 to 400Hz electric rpm.
 
yes, this is still the actual configuration

torque 0,7285 1,457 2,1855 2,914 4,371 5,828 7,285 8,74 10,199 11,65 13,113 14,57
eta conductor losses 0,183 0,736 1,655 2,943 6,622 11,77 18,39 26,49 36,05 47,09 59,6 73,57
iron losses rpm / Current 1 2 3 4 6 8 10 12 14 16 18 20
0,77 100 87,65 90,48 90,01 88,78 85,74 82,6 79,56 76,69 73,99 71,46 69,08 66,86
1,71 200 87,60 91,98 92,64 92,37 90,90 88,95 86,82 84,60 82,32 80,01 77,68 75,33
2,83 300 86,82 92,22 93,47 93,70 93,12 92,03 90,73 89,33 87,87 86,37 84,85 83,31
4,13 400 85,79 92,02 93,68 94,20 94,13 93,49 92,62 91,64 90,59 89,51 88,40 87,27
5,53 500 84,95 91,79 93,72 94,45 94,69 94,33 93,73 93,00 92,21 91,38 90,51 89,63
7,00 600 84,22 91,55 93,70 94,57 95,04 94,88 94,45 93,90 93,28 92,61 91,92 91,20
8,56 700 83,52 91,30 93,62 94,61 95,26 95,24 4,95 94,53 94,03 93,49 92,91 92,31
10,2 800 82,78 91,00 93,50 94,60 95,39 95,49 95,31 94,98 94,58 94,13 93,64 93,13
12,1 900 81,96 90,65 93,32 94,52 95,45 95,65 95,56 95,32 94,99 94,61 94,20 93,76
14,1 1.000 81,03 90,22 93,08 94,39 95,46 95,75 95,73 95,56 95,30 94,98 94,63 94,25
16,4 1.100 80,04 89,77 92,81 94,23 95,42 95,80 95,85 95,74 95,53 95,27 94,97 94,64
18,7 1.200 79,19 89,37 92,58 94,08 95,39 95,84 95,95 95,88 95,73 95,51 95,25 94,96

the red marked eta values are the ones i expect in the typical cruise mode.
 
F4P,

If you want to preserve the formatting of a table, you need to bracket it with the "pre" element (left of youtube). Even then, it will need some tweaking...

F4P said:
[pre]torque 0,7285 1,457 2,1855 2,914 4,371 5,828 7,285 8,74 10,199 11,65 13,113 14,57
eta conductor losses 0,183 0,736 1,655 2,943 6,622 11,77 18,39 26,49 36,05 47,09 59,6 73,57
iron losses rpm / Current 1 2 3 4 6 8 10 12 14 16 18 20
0,77 100 87,65 90,48 90,01 88,78 85,74 82,6 79,56 76,69 73,99 71,46 69,08 66,86
1,71 200 87,60 91,98 92,64 92,37 90,90 88,95 86,82 84,60 82,32 80,01 77,68 75,33
2,83 300 86,82 92,22 93,47 93,70 93,12 92,03 90,73 89,33 87,87 86,37 84,85 83,31
4,13 400 85,79 92,02 93,68 94,20 94,13 93,49 92,62 91,64 90,59 89,51 88,40 87,27
5,53 500 84,95 91,79 93,72 94,45 94,69 94,33 93,73 93,00 92,21 91,38 90,51 89,63
7,00 600 84,22 91,55 93,70 94,57 95,04 94,88 94,45 93,90 93,28 92,61 91,92 91,20
8,56 700 83,52 91,30 93,62 94,61 95,26 95,24 4,95 94,53 94,03 93,49 92,91 92,31
10,2 800 82,78 91,00 93,50 94,60 95,39 95,49 95,31 94,98 94,58 94,13 93,64 93,13
12,1 900 81,96 90,65 93,32 94,52 95,45 95,65 95,56 95,32 94,99 94,61 94,20 93,76
14,1 1.000 81,03 90,22 93,08 94,39 95,46 95,75 95,73 95,56 95,30 94,98 94,63 94,25
16,4 1.100 80,04 89,77 92,81 94,23 95,42 95,80 95,85 95,74 95,53 95,27 94,97 94,64
18,7 1.200 79,19 89,37 92,58 94,08 95,39 95,84 95,95 95,88 95,73 95,51 95,25 94,96[/pre]

the red marked eta values are the ones i expect in the typical cruise mode.
Click to expand...
 
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