Miles wrote:Next decisions:
How many slots? 18, as modelled or I could possibly reduce it to 15?
How many poles?
But they will affect the amount of copper in the links between coils... If I used 15 slots and 14 or 16 poles, most of the coils could be linked to their adjacent partner, I think. As I'm intending to use rectangular copper strip and the connections are outside of the case this would be an advantage...Lebowski wrote:These choises have no effect on efficiency... just make sure the motor is physically big and has lots of copper in it.
Miles wrote:But they will affect the amount of copper in the links between coils... If I used 15 slots and 14 or 16 poles, most of the coils could be linked to their adjacent partner, I think. As I'm intending to use rectangular copper strip and the connections are outside of the case this would be an advantage...Lebowski wrote:These choises have no effect on efficiency... just make sure the motor is physically big and has lots of copper in it.
Need to find out the trade-offs WRT the winding factor?
Thanks bearing. That's a very good point. I guess the "unbalanced" rotor/pole combination would be noisy, too...bearing wrote:I don't think a stator with 15 teeth is going to work well. With 14 or 16 poles, windings will, as you say, be put in groups of 1/3 of the diameter. Every time a phase pair is energized it will "bend" the rotor(s) and shaft. See the summary at the bottom of this page: http://powerditto.de/15N14P.html
It might work better with an axial design with small diameter, but I would personally avoid it.
Lebowski wrote:What is a winding factor ?
18t and 20p (winding factor 0.945) seems the best solution for me, I think. I'll see what a 12t layout looks like, though.bearing wrote: To solve this "imbalance", use twice as many teeth, which will put windings in two groups, on opposite sides of the centre.
Thanks. This is a good idea but ordinary heatshrink tube (even the thin stuff) might still be a bit thick walled to get a good fill factor? Maybe I can get some very thin walled heat shrinkable Kapton/Polyimide tubing in a suitable size? Otherwise, I was planning to use a layer of Kapton tape.Lebowski wrote:an idea which I had with this respect that you may find usefull:
at farnell they sell (quite cheaply) heatshrink tube in all diameters and up to 5 meters in length (5 meter for 4 euro
for the thinner stuff). You can sheeth your copper strip with heatshrink tube before winding it to isolate it....
Miles wrote:I was planning to use a layer of Kapton tape.
Lebowski wrote:I found it very interesting that apparently there are more than one way of generating electro magnetic force
and that different motors use different principles.
rhitee05 wrote:Your desired speed/torque/Kv also might be a factor in choosing the number of teeth/poles. All other things being equal (which they won't be...), the 18t motor will have 2/3 the speed of the 12t motor, but 1.5x the torque (not accounting for different winding volumes, etc). You could still make the Kv of either motor almost anything you wanted, but this is probably a good time to decide about what range you're shooting for.
If the core is epoxied, there's only the exposure between the two coils to worry about..... A Kapton "washer" separating them would sort that.rhitee05 wrote:Miles wrote:I was planning to use a layer of Kapton tape.
That's what I would have suggested, even using really thin heatshrink you'll end up with 2x the thickness between wraps. Kapton tape should be pretty easy, since you could just apply it to one side of your copper strip and then roll the whole thing up.
The insulation thickness values seemed quite high, too. But with only 3 turns x 2 .......rhitee05 wrote:8mm x 1mm is pretty hefty stuff - comparable to 8-ga round wire. Bending radius could be an issue - you'd probably need to round the edges of the lam stack to accommodate it. Definitely suitable for a high-current motor, though...
Thanks Eric. That would be very useful. I'll model up the stator modules properly for 12t and 18t layouts.rhitee05 wrote:If you want to provide me with some of the dimensions you're looking at, I can toss together a quick FEMM model as a place to start considering some of the tradeoffs.
Miles wrote:Reworked 18t stator: