1 view (last 30 days)
ozpom on 18 Apr 2013
Answered: Steve Miller on 25 Jun 2021
Please can someone help me.. I have built the simple pendulum in simmechanics; using the same process as shown here: http://blogs.mathworks.com/seth/2009/02/26/modeling-mechanical-systems-the-double-pendulum/
My problem is when i calculate the time period for a 200mm long string, I get 0.9 seconds.
When I carryout an experiment, I get between 0.9 - 0,99; various times...
When the results are inputted into Excel, I get 0.9 seconds on the graph
But when I put all the same conditions into SimMechanics, the results are different and show that after 3.5 seconds, the pendulum has only just reach half way through its cycle.
Now I can get the simulation to respond correctly by increasing the mass from 0.431Kg (the actual plumb bob weight) to above 431Kg. After doing this I get the time period to 0.9. At first glance I thought it was a units problem, but they all look ok.
Can anyone please clear this up for me, as its driving me mad. By the way, Im only a novice so please be gentle....

Steve Miller on 25 Jun 2021
Hi Ozpom,
The problem could be the model (perhaps the center of mass or inertia values and locations are not where you intended) or the differences you see with respect to theory are due to numerical disturbances. Try making the step size 10 or 100 times smaller and see if you get a different result. You can always post the model and we can take a look at it.
--Steve