Rubber Motor Optimization

[coachchuckaahs]

This question posed by email:

Since there is no limits in the rubber weight limit, it is really intrigued our students about where to start in optimizing the flight. Right now, we are following your advices in using rubber linear density as a primary parameter. However, as we start to build/ test, we were debating where to start the rubber motor:

1. Should we start with rubber weight: I.e same rubber weight across different rubber nominal width? Which will generate a whole bunch of various rubber length.
Or,
2. Should we start with same rubber length?

Thank you so much

My answer:

This is a two-parameter optimization, rubber density (or width), and rubber mass (or length). You are correct in holding one parameter steady while varying the other.

Your question is whether to hold mass or length constant.

I think either will work. HOWEVER, if you hold length constant, the mass changes, and so the total mass flying changes with each motor, which can change the flight characteristics. If you hold mass constant, then the length changes, but the totally flying device does not change. Therefore, I believe mass is the better parameter to hold constant while changing density.

Alternatively, you could hold density constant and change mass to optimize.

In either case, once you have optimized one parameter at a given value of the second parameter, you will want to change the second parameter and re-optimize the first.

Finally, you could also introduce the concept of DOE, or Design of Experiment, which would develop a sparse matrix of mass/density combinations to test, and MAY get to a 2-parameter optimum faster. But that is a fairly advanced approach.

Coach Chuck