Poko Mac

12-01-1998, 08:30 PM

Just a quick (hopefully) question to the group,

I am demonstrating how to calculate angular momentum of several segments

from filtered co-ordinate data using Microsoft Excel. To do this the

angular velocity of the segment, in free body state, must be obtained.

My problem arises when the segment moves out of the 0 - 90 degree

quadrant. If you use the simple TAN relationship (difY/difX) to

calculate the angle of the segment from the raw co-ordinates then as the

segment approaches 180 degrees the angle with the horizontal approaches

zero, which mathematically makes sense. In the second quadrant an

anti-clockwise displacement would lead to a negative angular velocity

(if you utilise the same angle as used in the first quadrant) which goes

against the sign convention.

In practice you could take this angle from 180 or add it to 90 degrees

to get the full angle of the segment, assuming your right horizontal is

zero degrees. The problem is the spreadshhet, without more complex

calculations, does not know what quadrant the segment is in! Is there a

simple way to calculate the 'true' angle for the segment, i.e. the true

angular displacement from the original?

Maybe i am overlooking something fundamental or it could be more

involved, has anyone out there solved the problem using spreadsheets or

any other information would be gratefully accepted.

I know i could solve the problem using C++ or Matlab but the

demonstration was as much about using MS Excel as calculating the

angular momentum.

As usual i will post a summary of replies.

Thanks, Dave

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I am demonstrating how to calculate angular momentum of several segments

from filtered co-ordinate data using Microsoft Excel. To do this the

angular velocity of the segment, in free body state, must be obtained.

My problem arises when the segment moves out of the 0 - 90 degree

quadrant. If you use the simple TAN relationship (difY/difX) to

calculate the angle of the segment from the raw co-ordinates then as the

segment approaches 180 degrees the angle with the horizontal approaches

zero, which mathematically makes sense. In the second quadrant an

anti-clockwise displacement would lead to a negative angular velocity

(if you utilise the same angle as used in the first quadrant) which goes

against the sign convention.

In practice you could take this angle from 180 or add it to 90 degrees

to get the full angle of the segment, assuming your right horizontal is

zero degrees. The problem is the spreadshhet, without more complex

calculations, does not know what quadrant the segment is in! Is there a

simple way to calculate the 'true' angle for the segment, i.e. the true

angular displacement from the original?

Maybe i am overlooking something fundamental or it could be more

involved, has anyone out there solved the problem using spreadsheets or

any other information would be gratefully accepted.

I know i could solve the problem using C++ or Matlab but the

demonstration was as much about using MS Excel as calculating the

angular momentum.

As usual i will post a summary of replies.

Thanks, Dave

__________________________________________________ ____

Get Your Private, Free Email at http://www.hotmail.com

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For information and archives: http://isb.ri.ccf.org/biomch-l

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