We’re doing failure analysis on a DC generator at work. It has 41 commutator segments on the armature. I want to draw the commutator in PowerPoint. I figure it would be pretty easy to draw each commutator segment if I had a gif or jpg of a 41-sided polygon to work with.
Is there an online “polygon generator” that can draw me a 41-sided polygon? I did some google searching, but didn’t find anything.
will this do?
Yea, I think that’ll work. Appreciate it!
Inkscape (free Open Source vector graphics drawing program) is another way to do this - you can draw polygons of any number of sides and size.
Why not just take a photograph of the armature, crop the background, and use it directly?
I note that a regular 41-sided polygon is tolerably close to a circle.
I like that wolfram lets you do one and two sided polygons as well.
GeoGebra will do that for you, along with a great many other mathematical things, and it’s free to download.
Off-topic, but since you already got your answer:
41 commutator segments? I would have expected something like 36, with lots of factors, not a prime number. At least an even number. Is this typical? Does the number vary all over the board?
You can make a pie chart in Word with 41 equal slices and then import it to Powerpoint.
I would actually expect the number of commutator segments to be prime. Or at least, relatively prime to the count of some other part on the device, but primes are an easy way to get relative primes.
It’s very easy in Adobe Illustrator. Just tap the page with the polygon tool and type in the number.
Why?
Because if the commutator segments and whatever they interact with have a common factor, then you could get the same performance by decreasing both by that factor and increasing the rotation rate.
You just stole my words! 
Inkscape is quite practical for those tasks.
I looked at images of commutators in a Google image search, and most of the ones with many segments I saw had an even number of segments. The number varied, and of the ones I counted them on had 16, 19, 20, or 22 segments. There’s one on the Wikipedia Commutator page with only three. So I’m going to guess that it does just vary all over the board.
(As a EE, I should probably already have known all this, but in the third term of undergrad electromagnetics, where electric motors were taught, we had a professor who liked to tell stories rather than teach, so I’m weak on this subject.)
Yea, 41 segments. Four-pole generator.
They used a “wave winding” to wind the armature, where there’s a single winding between segments 1 and 20, 2 and 21, 3 and 22, etc.
It’s just like the drawing shown at the top of page two in this document, except it has 41 commutator segments instead of 21.
:smack: And here I thought the reason was:
This is not the answer at all. Many motors have an even number of segments. In fact, if the design allows it it will almost certainly have an even number of commutator segments.
There are several ways of winding an armature.
In a wave type winding the number of commutator segments equals the number of coils and this number must necessarily be prime relative to the pitch so that the electrical path ends where it starts.
Suppose you have 7 coils & segments, start at segment 1 and skip 2 segments (Pitch 3) with each coil, then the coils go: 1-4-7-3-6-2-5-1. If you have coil and pitch numbers which are not prime to each other then the winding gets back to the starting segment without having touched every commutator segment.
Suppose 9 coils & segments and pitch 2: 1-3-5-7-9-2-4-6-8-1 … works fine
Now 9 coils & segments and pitch 3: 1-4-7-1 … nope, back to 1 without touching 2, 3 ,5,6 etc.
Of course, one way to ensure the pitch and the number of segments on the commutator are relative primes is to make the number of commutator segments an absolute prime and this way the same commutator arrangement can be used with different pitches.
In other types of windings the number of commutator segments geometrically can be even and I think I have never seen one which was not, in fact, even.
Google “lap winding” and “wave winding” for more information about the relationship between number of commutator segments, coils, poles, etc.
You posted while I was composing my earlier post. Here is the order of your machine with 41 windings and pitch 19: 1, 20, 39, 17, 36, 14, 33, 11, 30, 8, 27, 5, 24, 2, 21, 40, 18, 37, 15, 34, 12, 31, 9, 28, 6, 25, 3, 22, 41, 19, 38, 16, 35, 13, 32, 10, 29, 7, 26, 4, 23, 1.