OK, I'm out of town right now, so not able to search through boxes. However, going back over the documentation here, I found the MOSFETs that I was using: IRT 3205. They got hot to the touch (around 65c), with a heatsink bolted on (no sink grease).
There's a fair amount of detail on this page:
https://forum.sparkfun.com/viewtopic.ph ... 8&start=30
There's a picture of my set-up, and Mee-n-Mac wrote out a circuit diagram that should help (it's not what I'm actually using).
The MOSFET's that I was using were blowing at times, due to mechanical issues on the AEG. I really felt that the electronic portion of the build was solid. Once I switched to a "tuned" AEG to test, the heat from the FET was dropping very low. I was planning on using heat measurements of the FET as a diagnostic criteria. As you saw your tuned gun start to heat up, it would indicate that the system was pulling more amps to drive the gear box, indicating that the gearbox was starting to lose tune.
All that being said, my plan the whole time was to have the MOSFET easily replaced, and in a location where I could easily heatsink to the outside world. My plan was to build some kind of metal cover or plate, with some beefy connectors to the power, drain, and trigger legs. The metal cover would sink the heat to the outside world, but screw into the frame somewhere, protecting the circuit. I never got close to the implementation of this.
I think the project is worth doing, I'm just heavily time constrained these days, and I don't have a working AEG.
A ton has changed since I last touched this thing. One thing I would DEFINITELY look at is a higher power (clock speed) processor. I think I was hitting some limits using the basic Arduinos that I was using. I would seriously look at prototyping this with an ugly Due, knowing it was never going to fit in a gun, then sinking money into developing a custom driver board. As it was, the displays that I was using, one of the reasons I wanted them was because I could 'offload' the graphics programming to the display boards, and just let the Arduino drive the gearbox and look for critical sensor inputs. It really wasn't going to be up to doing anything graphically as well as those tasks.
I'll keep looking through my boxes, and I'll keep an eye on here to see how things are going.