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:

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?