Thanks for the CAD trick -- I will get one of the students to try it!
An equivalent old-school method uses pitch diameter circles and tangent lines connecting them to calculate the wrap angle on each pulley, and then get center distance from the resulting two arcs and two lines. One such calculator can be found here:
http://www.gizmology.net/pulleysbelts.htm
Using that one I got 4.773 inch C-C for a 110 tooth belt connecting a 12 tooth pinion to a 45 tooth pulley at 3mm tooth pitch. Will check that against the CAD result before we cut holes in metal. Measure twice ...
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)