James thats not entirely true in that were talking about potential energy in flywheels, not the fact that his 2kw motor is producing 2kj/s of energy of energy, which obviously affects how fast the disc spins up, but not the amount of stored energy. In terms of what Mark and John where talking about, the MOI of a mag rotor would have little bearing on the final outcome. So ignoring the effects of the motor in that equation is entirely justifiable :-p

Having said that, with talk of LEMs and such, I would have thought the MOI of a LEM rotor, especially in terms of featherweight weapons, is reasonably substantial, and so should be taken into consideration.

With reference to Marks question, taking it to the extreme of, for example, an antweight spinning blade attached to a GPA 750, then obviously the MOI of the rotor would have a big effect, but more importantly its about the maximum potential K.E your flywheel can store- a smaller, lighter disc, will not have such a large potential. This means that it does not take your very big powerful motor much time to fill it up (a yuck way to put it, but you get my point) with energy. So, choosing some fairly arbitary values, your disc may have a maximum potential of 1kJ, and your motor may be 4kW- or 4000 Joules/sec, so obviously the motor will fill (yuck again) the disc with energy rather quickly. So, as the light disc is rapidly dissipating its energy into its opponent that its just hit, the motor is pumping loads of energy back in, thus keeping the disc going and going- its the relationship/ratio between the power of the motor and the energetic potential of the disc. I suppose this could bring us to the same point that the flipper folks have got to- trying to find the sweet combination or golden ratio between larer bore (so more powerful) rams which consequently take longer to fill up, and less powerful rams which actuate more quickly. In our case, its a question of having a bigger/heavier/faster disc that takes longer to gain its max potential K.E, or more powerful motors/bigger batteries that get a disc with less potential up to speed more quickly, and keep it there.