IWP parameter quantification

Hmm, it’s been a while. Now that the holiday period is over and I’ve settled into a new home, I’ll hopefully have more time for my hobby projects!

Getting back to the IWP…

So far we have a symbolic model which shows how different system parameters affect the dynamic response of the system. For this particular model, designing and/or measuring system parameters should be relatively painless, but requires close attention to the model and how its parameters are defined.

A given parameter might be quantified by experiment, calculation from first principles, or by a numerical model depending on the complexity of the respective approach. A simpler approach might mean a less accurate result, so it becomes important to identify and meet a reasonable level of accuracy.

Relative accuracies may be obvious: For pendulum dynamics, the mass at the “plum-bob” end needs to be known more accurately than the mass at the point of rotation. For absolute accuracies or less obvious cases, my rule of thumb is to take two approaches, where possible, and aim to cross verify the results to at least 2 significant figures. Odds are that the error stack-up of the model and its parameters will represent the actual system dynamics pretty well.

So what did I do? I used a mechanical CAD package, Solidworks, to do the work for me:

I verified the masses (wheel and pendulum) by weight scale and calculated the rotational inertia of the wheel to good agreement with Solidworks. Subsequently, I would’ve inferred the pendulum chassis inertia to be in the right ball park as well.