e-mails from Mechanisms Professor

This is what i have to deal with

11:44AM
It has been brought to my attention that there is an issue with problem 2 and therefore problem 3 !!

The issue is that when you successfully find the 4 bar for moving through the 3 positions, the resulting 4 bar goes through a branching condition !! This was my mistake in not checking the problem out completely before hand.

For problem 3a, if you enter the info generated the motion will not match the desired positions. This is OK and do not sweat it.

For problem 3b, if would be "nice" to vary point B1 to get the 4 bar to not branch, but you are only required to find 6 other attempts as per the test. If you do not find a "good" non branching mechanism in 6 tries, then just say so and move on!!

These issues are real life to the headaches of mechanisms designers. Not what I wanted, but not a waste of your time either!!! Now you know the hidden issues with what looks like straightforward solutions.

Sorry

Steve


1:47 PM
The Fourbar program is a real pain when dealing with negative numbers and link rotations!!!

To get around this issue, best to set the following types of values for initial conditions:

Min Theta 0 degrees
Max Theta 360 degrees
Delta Theta 5 degrees
Omega 2 rad/sec

This will rotate the linkage in the "wrong" direction, and it will not be limited to just the 3 desired positions, but at least it will move and not give silly error messages!!

All of the previous problems I had run in Fourbar were entirely "Positive" in the data so I had not seen this coming. I did email the book author to say "What Gives"

This should help

Steve

6:18PM
I have gotten an answer from the book author, and most of our issues are that we have an older error filled version!!

Even the McGraw Hill website that was supposed to have a better version that I downloaded today is still Rev 2.0.3. Norton gave me the "correct" results on his Rev 4.01 version.

So the short answer is that this problem makes the Fourbar problem have issues that are not going to be fixed before Tuesday 10 am!!

So give my past info a try or 2 , and then write up what you did find if anything, and them MOVE ON !!

Sorry about this!!

Steve

8:08 PM with an attached program
The book author just emailed me a version from last night for Fourbar that is supposed to be all OK.

If you can, please try this new version once to see if all is OK or not.

Thanks

Steve