Simscape: The derivative of position in a direction not equal to the velocity
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I am using simmechanics 2g to simulate a robot. On one of the points on the robot, the velocity (plotted using scope) in the horizontal-x direction does not match the time-derivative of the position. This seems to defy my understanding of Newtonian Mechanics. Has somebody faced similar situations or know why this problem arises?
Note: There are no external forces provided in the horizontal direction although there is one provided in the vertical direction.
2 Comments
Rebecca Krosnick
on 23 Dec 2015
What equations and blocks are you using to generate the time-derivative of the position and the velocity? Can you also provide screenshots of the scope plots?
Answers (1)
Sebastian Castro
on 25 Dec 2015
In general, I wouldn't trust the Derivative block's results very much. This block only does an approximate derivative of a signal, which is highly dependent on the simulation step-size taken, and has no continuous states or error control.
Some useful links:
Try doing it the opposite way: Use an Integrator block on the velocity signal and compare it to the position. This will likely look a lot better.
- Sebastian
4 Comments
Sebastian Castro
on 28 Dec 2015
Hmm... It could also be the Max step size parameter in the same solver settings. You could try reducing it and seeing what happens.
- Sebastian
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