7 replies · posted

Help on array understanding!

Hi, I have got this array to work but accidentally & I'm trying to understand why as the math doesnt seem to add up.  Would appreciate any help.   Creating a barrel of a wheel.  I know this is the wheel excercise but i've already done the tire array & spoke array  but the rim is not quite working out like those did for some reason.

Created 40 vertex circle and deleted all but 5 vertices at the top (to be the cross section of my barrel).  I extruded the edge to create on section of the rim.  5 vertices is 1/8 of the total 40 vertices that i made the circle with so i expected to need to use 8 sections however it seems to be taking 10 @ a 36 degree rotation of my added empty to make it work.   If i use 8 sections at 45 degree empty rotation that i expected to work I get the result below. -see image

  • Huh, what a weird problem.  I've been doing the math, and the angles match up correctly on a theoretical level.  I have no idea what's up.

  • Ahhh, after talking to someone about it, yes you are rotating the 5 vert segment around, but the space between the first vert of one segment and the 5th vert of the previous segment isn't filled in, so you're getting gaps in your mesh.  Hopefully that makes sense.  It's kind of a weird off by one error visually.

    • silentheart00 Yeah, i've been having a feeling thats something to do with it for a while but havent figured out how to fix it yet.  I can get it to work at 32 v total , 5v per section & 8 sections with 45 deg rotation on my empty but the math doesnt seem to add up for that for me yet.   Thanks for your help/time! :)

    • ccurtisdd1 No problem.  Yeah, the math is weird, but you can solve that by adding an extra vert and just make the calculations based on total verts-1.  Hopefully someone with a better explanation can pop in and help shed some light on this.

  • Hi curtisdd1. A lot of people make mistakes like this when it comes to 'circle math',

    Look at it this way: You made a circle with 40 vertices. That means 40 edges, right? By deleting all but 5 vertices, you were left with 4 edges. So to make a complete circle again you need 10 of those to get your 40 back.

    Why doesn't this work with the verts? Well a line always has one more vertex than edges. But in a circle the first and last vertices are merged. So it seems that you have the same amount of vertices and edges. So you think it makes no difference if I count the verts or the edges. But by cutting a 'slice' out of the circle, you are left with a (bent) line, so one more vertex than edges!

    • spikeyxxx Thanks a bunch !  I'm still gonna have to think a little more about how to do the math but i get it overall.  Feeling a little silly too now lol.  I felt like there was something there i was missing with the edges but couldnt put my finger on it .  My math is rusty but pretty solid  but I'm just beginning to learn to think about this stuff -  edges , vertices & such & combine that with the math.  Again thanks to you & silentheart00.

    • spikeyxxx Thank you!  That's the missing puzzle piece I was looking for!  Good to know, thanks!