solidworks model help

[Byron md]

I am drawing a pentagon (yellow) with sketched lines on the front plane, the sketch is symmetrical about the Y axis, the top point of the pentagon is at the origin. I then draw a circle on the right plane at the top point of the pentagon (at the origin) and extrude a sweep using the circle as the profile and the pentagon sketch as the path to create the round bar pentagon. I then create a 30 degree plane from the top plane through the origin and draw a circle on that plane with its centre coincident to the origin and extrude it to form the short strut (blue) at 30 degrees, I then mirror the short struts to the other corner points of the sketched pentagon. In a new part I then create my long strut (pink) simply with a circle and extrude. I then create an assembly with the pentagon and insert the long strut mating it coincident and concentric to the short strut. I then insert a copy of the pentagon mating it the same way to the other end of the long strut. Then repeat that process on the other short struts. The final strut that joins the 2 inserted pentagons is not lining up and too short as seen in the pic. Why???

[cedar]

30 degrees must be wrong.

[Byron md]

So is this a mathematical problem? Do you know how I would calculate the correct angle?

[jkristia]

what if you measure the angle between the 2 first hex poles (top left, bottom left) is that 60 degress, then again between the 2 bottom poles, is that 60 degress too ? or is it maybe 60.5 degress ?

 

I just tried to trace over the drawing (not very accurate) and that gives my the first angle to 61 the second to 63, but of course this will only work if it is a true plan view.

 

Just an idea

[JD Mather]

So is this a mathematical problem? Do you know how I would calculate the correct angle?

 

http://home.pct.edu/~jmather/Content/cad237/soccer%20ball.gif

 

I'll have to look around a bit - but I think I had to take the angle out to 8 decimal places. Try 37.3773681407°.

[cedar]

I’ve seen soccer balls modeled before. They used a number of layout sketches to do the math and set up Planes to model the pentagrams. Once you have a section similar to your picture with the exact compound angles… that is inserted into an assy multiple times and mated to make the whole ball. I’m sure this can be done so changing a diameter in the layout sketches updates the finished ball. Let us know how it turns out.

[cedar]

I couldn’t stand it, I’ve seen soccer ball model so much and yet it looked so easy… I had to try. Once I started I saw why it is tricky… the bottom pentagon is rotated and the angle calculations have to include that rotation. My solution was to draw a 3d sketch (red) between the pentagon centerlines, top to bottom, and make the line segments equal.

 

I cheated a little, I used a block for the pentagon sketch, and adjusted the block till all the sides were equal… kool to watch the whole ball update… but I did not calculate the proper side lengths with the sketches. I’m sure it can be done though.

 

It’s not the sweep frame your drawing but the point is to use sketches and constraints to do complicated math.