You're telling me all rumble motors are created the exact same way? They all have the same specs?
They all run on the same number of amps and volts? They all vibrate as soft as the Wii U Pro Controller's rumble?
No, they have different specs. Volts, amps, max rumble, speed, weight etc. But they probably all have a similar efficiency ratio, ie, the fraction of energy wasted to heat, noise, etc. In this case, the actual power used is fixed by the controller, let's call it 5W for convenience, since I don't know the real value. I'm claiming, and I could be wrong, that 5W worth of rumble would feel similar with different rumble motors. You could put in a smaller weight motor which would vibrate faster for the same 5W, but not as much strength. That would feel different, but not really stronger, right?
He wants twice the total rumble feel for the same power. To get that, you would need to double the efficiency of the motor. That's only theoretically possible if the efficiency is less then 50%, but I think it's higher then that, right? It's not an incandescent light bulb. If it is less, well, doubling efficiency is difficult. It would be expensive. Imagine taking a pickup truck that gets 12 mpg, and trying to make it get 24mpg, with the same weight, the same HP, the same tourque, etc. If we have the technology to do that, it's going to cost a lot more money, placing that truck outside the price range it was originally designed for.
Of course there are motors out there that have a higher theoretical max vibrate, possibly even in the same physical size, but they will need more power to get there, right? Unless there really is an affordable one with double the efficiency, but if the efficiency is already higher then 50%, that's impossible. Does anyone know the typical efficiency for a vibration motor? Isn't the normal efficiency of an electric motor in the 80's to 90's range? You can't double those. There just isn't enough wiggle room in the efficiency rating to cause the kind of change he wants. Granted, I don't know the equation, which could be nonlinear, between actual power used and perceived rumble effect, but I doubt you could achieve 100% increase in perceived rumble for a 0% increase in power under any conditions. Maybe by messing with the parameters you could get 10-20% increase, but not 100% as desired.