Hello. I'm new to SystemModeler. I'm attempting to learn the software with highly simplified experiments/models. At the moment, I'm trying to model a rotating a mass that is moved by a prismatic joint (representing a simplified hydraulic cylinder) as shown in Image1. With a combiTimeTable and position source, I animated the model. The smoothness of the combiTimeTable was set to ContinuousDerivative. The relative distance between the prismatic joint's frames, s, is shown below in Image2. This is a screen grab in Simulation Center. This is, indeed, the profile that I intended to input. The velocity profile of the prismatic joint, v, is about what I expected it to be as displayed in Simulation Center. (Please see Image3) As you can see, the initial position profile that I built in Excel for the combiTimeTable is based upon nearly constant acceleration and deceleration. The velocity profile isn't quite as smooth as I'd like it to be at the end of the acceleration phase and at the start of the deceleration phase, but things here aren't horrible. My main concern relates to the acceleration profile. And here is the meat of my question... When I plot the prismatic joint's acceleration, a, I get a very noisy plot. Considering my use of a combiTimeTable to control the length of the prismatic joint, can I control the filtering/averaging of the prismatic joint's acceleration? I'm quite sure I'm doing something foolish here. Thanks in advance for any help/advice that might be offered.

Hello Johan. I just finally found time to check your suggestion. It worked perfectly. You just helped me better understand where and when to use position, velocity, and accelerate to "drive" motions with combiTimeTables. Thank you. I have a few more things that I'm trying to sort out. If I can't these things sorted through on my own today - I may post about these stumbling blocks soon. Again, thank you for so kindly helping me get past my combiTimeTable confusion. Dave

Dave, after looking at your spreadsheet I see that you start by defining the acceleration and then calculate the speed and position from that. In that case I'd use an `Accelerate` component, with: `Modelica.Mechanics.Rotational.Sources.Accelerate accelerate(phi.start = 3.141592)` and "drive" the model that way. Attachments:

Hi Johan, Thank you very much for the help. I can't believe that in all of my playing around with this, I never actually checked the documentation for the Position source. Your reply was very helpful. So the resulting revolute acceleration in SystemModeler looks like this: The acceleration profile used to build my position table looked like this: Understanding now how the acceleration profile is developed by the Position source, it seems that I either have to live with the acceleration approximation that results from a position input table or, perhaps, use a Speed or Accelerate source with an appropriate table when I'm inclined to use a combiTimeTable input for one reason or another. Before I close out this question in my mind, may I ask you for your advice here? Suppose that a customer or employer of mine sends me the excel sheet that I attached in my earlier post. If I need to use this tabulated motion profile with a SystemModeler model, what would be the most accurate way to drive the revolute? Should I use a combiTimeTable to input position, speed, or acceleration to the revolute and use some appropriate f_crit filter frequency? Should I fit a curve to the tabulated position, speed, or acceleration data and then use a RealExpression block with an appropriate rotational source? Or is there a better way to "instruct" the SystemModeler revolute to accurately follow the motion profile in excel that I'm not thinking of? Thank you for all of your help!

New to SystemModeler - How do I smooth acceleration?