Kinematic Simulation - To do or not to do...

Over the last few months, I have noticed increased activity in terms of the SOLIDWORKS Motion productline. We have handled a couple of projects for customers, and the upcoming Motion training class (March 18, 2011) at Cincinnati, OH is three-quarters full.

Here are some general guidelines that can help beginners get a foothold into workflow techniques in kinematics and dynamics using SOLIDWORKS Motion. First of all, I should mention that while the outputs can be extremely invaluable, Motion does require a little bit more persistence than the other Simulation tools in the SOLIDWORKS portfolio. The product is great, but such is the nature of the beast. Often times, I find myself having to input parameters, and interpret results to understand why a mechanism did what the simulation says it did. Not all the time is it pre-emptively intuitive in terms of what to expect. If the user approaches the model with an open mind, and is willing to try out a few variations, the answer is not too far away.

So, here are some basic guidelines to begin with Motion:

1. Begin with the assumption that the mates may have to be re-done for motion analysis. In my experience, there is a cut-off point after which it is quicker to just re-create mates according to the intuition that motion uses, rather than the way we would possibly put a SOLIDWORKS assembly together. This particularly helps get rid of redundancies right from the beginning, and avoids issues later on. I often create a separate configuration for Motion analysis, where I suppress/delete all existing mates, and build my own set of mates in accordance with the motion project.
2. Start simple, and add complexity – I often start by mating two components together, and turn on gravity. Observing their behavior, and fixing the mates between them right away will be the quickest way to get it right the first time. Add one or two components at a time in the same fashion, and get the mates working as a whole unit. This will also help troubleshoot redundancies as they occur, rather than having to deal with a bunch of them at the end.
3. Use sample loads to verify mate setup – often enough, I have added random loads to make sure the model is responding in the intended fashion. I start this while I work on the previous step (step 2 above), and thus validate my mates accordingly. This maintains the logic, and allows you to think forward, rather than look back at what went wrong.
4. Finally, use the mechanical mates in SOLIDWORKS as much as possible – The mechanical mates are great ways to avoid redundancies. For instance, when I add two standard mates (like a concentric and a coincident mate), I have a good chance of creating a bunch of redundancies. However, a hinge mate, in this instance, essentially does the same function, but provides adequate constraints without redundancy.

With some practice, and good systematic techinques, you would be surprised as to how valuable this toolset will become in your Simulation arsenal.