Is odd better than even? 4

[PhilBW]

Another engineer and I were discussing a design for a manifold and how many parallel channels we should use in this manifold. The other engineer said an old timer once told him to use odd numbers whenever possible when designing things. He said that is why most wheels have an odd number of spokes. The old timer didn't explain why odd numbers are better. I've seen many designs using even numbers and they seem to work fine.

Has anyone else heard this? Does anyone have an idea why odd numbers of things might be better than even?

Phil

 

[byrdj]

looking at "manifolds"
for auto engines they are mainly 4,6,8,10,12,16, etc
for steam turbines are 2,4,6, and 8

 

[racookpe1978]

That's because "manifolds" are stationary - split evenly (usually, as in turbine casings) between the top and bottom of the two casing halves to evenly suck air from the rotating turbine blades.

The simplest division is two outlets (one above and one below) but that tends to create "bubbles" or surges in the delivered gasses. 4 connections is better since that gives nice even fixed nozzles every 90 degrees: 45 up and down from the split line. The more the connections to smoother the pressure.

 

[spciesla]

I'm waiting for e & pi to enter the conversation! How about the golden number.

 

[SomptingGuy]

Golden number already hinted at: fib(N)/fib(n-1) where n is large.

- Steve

 

[drawoh]

A simple example of odd /even is 3 leg stools/chairs are better than 4 leg.

Are you suggesting that a tripod works because it has an odd number of elements?

When designing gears or sprockets you should have at least one with an odd number of teeth the maximize wear. When both gears are even not every tooth with mesh with every other tooth of the second gear. It is similar for sprockets, where a roller element will not engage every tooth.

Perhaps you are thinking of a hunting tooth? Instead of meshing a 40[ ]tooth gear with a 20[ ]tooth gear, you would change the big gear to[ ]39 or 41[ ]teeth.

JHG

 

[FeX32]

It's not odd or even.
It's 1.6180339887......



Fe

 

[GregLocock]

"Instead of meshing a 40 tooth gear with a 20 tooth gear, you would change the big gear to 39 or 41 teeth"

As you would if you were a gear manufacturer, and observe in passing that it is the lack of a common factor that is important, rather than primeness as such.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ivymike]

yes, as I mentioned above, the hunting tooth is good for a fight.

 

[telecomguy]

Even if odd is better than even, I find it odd that even the Odd "Couple" was even.

 

[SomptingGuy]

WolframAlpha has the golden section shown as

-2sin(666°)

THere is a hidden message here I'm sure.

- Steve

 

[drawoh]

... As you would if you were a gear manufacturer, and observe in passing that it is the lack of a common factor that is important, rather than primeness as such.

Nor does the oddness or evenness matter.

JHG

 

[FeX32]

Yes, Steve got it. It's not odd or even it's evil

Fe

 

[tbuelna]

"Even if odd is better than even, I find it odd that even the Odd "Couple" was even"

Impressive and original! That's the second most insightful post I've ever read on this website.

As for the original question regarding whether, in general, is odd better than even when designing something? The answer is: It all depends upon the application.

Most religious types would agree that God is the ultimate designer. And most men would agree that his best piece of work is the female body. She has one mouth, two eyes, one belly button, two big toes, and one heart. Odd, even, odd, even, odd, etc. Can any of you think of a more perfect design?