I''ve come across an engineering problem in the design of a robot I''m working on. I''ve tried searching the internet and I can''t find the data I need. I know from pervious experience that all you gamedevers have a good footing in geometry. My problem is this: I have a tank tread that is 64 inches long. It needs to go over 3 drive cogs that are in the shape of a triangle (two on the ground and one leading slightly above so it can more easily climb obstacles). I want the leading cog to move in a track from 0 to 90 degrees so the angle on the front (and theoretically the ease of climbing objects) can be changed. If I have two fixed points and a known distance to which all the line segments must add up, that''s pretty much the textbook definition of an ellipse. The two fixed cogs become the foci, now I just need to figure out the major and minor axes. Unfortunately, it''s summer, and I''ve forgotten the math I was learning just a few short weeks ago. If someone could give me the formula to get the major and minor axes from the distance between the foci, I''d be thankful. --------------------

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Yanroy@usa.com

Well the track runs between the focal points and to a point on the ellipse if I understand you correctly. So if t is the track length and d is the distance between the focal points then the combined distance from the focal points to a point on the ellipse, c, is c=t-d. The minor axis is 2*sqrt(c^2/4-d^2/4) or sqrt(c^2-d^2). Since c=t-d that is the same as sqrt(t^2-2*d*t). The major axis is d+c-d or c or t-d. That is just going to be a rough approximation since you don''t have points. You instead have cogs and the cogs have a radius.