I have not yet analyzed the performance difference between FETed and non-FETed in combination with the increased duty cycle. However, with a reasonable motor (say, 2.5 ohm or higher) there should be a linear increase. That is, whatever power level you get with the MOSFET mod, you should see a factor of about 2 or 3 increase in power delivery. This is because whatever the MOSFETs are doing, with the DC mod they get to do it 2 or 3 times as long (at full throttle anyway). I did video test runs with and without FETs, I've just been too busy with other things to analyze it
)
With higher performance, lower resistance motors you won't see a linear increase unless you've upgraded your battery. The stock ZZSE battery cannot sustain high current demands (say, anything above 6-700mA, around 10C) for more than a few seconds. If you need sustained high performance operation you'll want to try adding a second parallel battery or supercap to stiffen the power supply. (that gives me an idea for a project, a power monitor. Logs battery voltage and throttle position over time to reveal problems in the power system under actual racing conditions).
On request I'm happy to stack as many FETs as you want for a buck per channel (e.g., $1 for forward and $1 for backward) (If you want more than a deca-stack I'll need some notice to be sure I have enough FETs, and you'll be responsable for the necessary chassis mods
)
I don't usually do stacked FETs on SE's because they don't seem to need it. When I say 'seem' I mean 'I haven't yet gone to the trouble of dyno-ing various FET and motor configurations, and I haven't seen a difference in top speed when measuring with a video camera at 1/30th second resolution)'.
ph2t and I discussed this a couple weeks ago. He'll tell you it makes a difference, I'll tell you I don't yet have hard performance data either way.
I don't usually stack FETs because I when you're looking at 2 or 3 ohms of motor windings, the 0.05 or so of MOSFET on-resistance just doesn't make a significant difference for most people. Any type of battery upgrade (replacement, peak charging or overcharging) will get you better drag race performance, and I can't think of any other situation where 1-2 percent difference would even be noticable.
