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Message: [QUOTE="TallOne, post: 3810149"] I'm trying to use Excel to calculate the output shaft rpm of compound pulley systems. Pulley sizes are available in half inch increments. I've got Excel set up to calculate the ratio of the known input rpm and the target output rpm. I've got a table on another worksheet with the ratio of the driver(vertical column of half inch increments from 1 to 30) and driven(horizontal row of half inch increments from 1 to 30) pulley diameters. What I need Excel to do is take the input rpm, divide it by the target rpm, then search the ratio table for all the combinations of pulley diameters that will provide that target rpm. One complication is that I need it to do this for combinations of pulleys in mulitples of 2 (2,4,6...). For example when I have an input rpm of 1725 and need an output rpm of 150 I need to use a ratio of pulley diameters of 11.5:1. In a 4 pulley system the combination of a driver(1) pulley dia. of 3 inches and a driven(1) pulley dia. of 13 inches produces a ratio of 4.33:1. Then the second driver(2) pulley is on the same shaft as driven(1). If the second driver(2) pulley is 3 inches in dia. and the second driven(2) pulley is 8 inches that produes a ratio of 2.67:1. multiplying 2.67 and 4.33 meets the required total ratio of 11.5:1. I've got Excel set up to produce a factor tree of combined ratios that meet the total ratio needed to produce the target rpm. Where I'm stuck is how to get Excel to search the tables that are calculating rpm from known input rpm and calculated total ratio and then spit out the different combinations of driver(1)~driven(1) and driver(2)~driven(2) pulley diameters that produce the target rpm. I'm trying to use VLOOKUP and MATCH, but I only know enough about excel to be dangerous and it's not working. Any help, advice, and ideas would be most welcome. Thanks in advance, Rob... P.S. I'll also need to do some trig functions on the diameters to make sure that the belt is in contact with at least 120 degrees of both pulley's surfaces. I figure I can do that with a similar setup to calculating output rpm(using center to center distance and diameter).Again, thanks and sorry about such a long post. [/QUOTE]

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