This is something I would need to see to understand what's going on. The
basic lookup is no problem but you have all those calculated conditions that
need to be dealt with. If you don't get any other replies that solve the
problem and you are willing to send a copy of the file to me I'll see what I
can do. Let me know in this thread if you want to do that.

--
Biff
Microsoft Excel MVP


"TallOne" wrote in message
...
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.