[EricH]

John: The CIM weighs a lot more. That might be enough to put an FP in where a CIM could go. Just one of those accursed design tradeoffs that come with any design problem. And yes, I might use an FP instead of a CIM even if I could use a CIM. It depends on the application.

Back to what I was originally going to say...

I compete in the SAE Aero Design competition. There are three classes of planes, each with different power restrictions. Regular says "Thou SHALT use engine X with muffler Y, unmodified." Advanced says simply, "Your total stamped engine displacement must be less than or equal to Z cubic inches. Reciprocating engines only, please."

But the most interesting is the Micro class. There are no engine restrictions, other than that it has to be internal combustion (reciprocating) or electric. This opens up a wide variety; and my team has done both. Gas was our choice the first year, because we knew what we were doing. The next year, we chose a pair of electric motors instead. Different planes, same goal, different power, different results.

The plethora of options is one thing; it can make decisions harder. On the other hand, having few/no options makes them easier, but not necessarily. FIRST has struck a balance: You can use this number/type of motor, here are the motors.