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!

Dave, I quickly looked at your model. You're using a `Modelica.Mechanics.Rotational.Sources.Position` to drive the revolute joint. `Position` has to somehow derive the angular velocity and acceleration from the numerical input. From the documentation of Position: The reference angle is filtered and the second derivative of the filtered curve is used to compute the reference acceleration of the flange. This second derivative is not computed by numerical differentiation but by an appropriate realization of the filter. For filtering, a second order Bessel filter is used. The critical frequency (also called cut-off frequency) of the filter is defined via parameter f_crit in [Hz]. This value should be selected in such a way that it is higher as the essential low frequencies in the signal. I changed the `f_crit` in a simplifed version of your system to `0.1`, and that gave a nice angular velocity and acceleration. Attachments:

New to SystemModeler - How do I smooth acceleration?