When calibrating the ESC's I found that one of the ESC's is defective, and I just do not have time to order a new one from HobbyKing. So, my other option is to buy one from a local store. The problem, however, is that I did not find the same kind of ESC's that the 3 other ones are. I can find ones with similar specs, but just not the same exact one. Will that affect how the quadcopter runs?
Different ESCs running different firmware can have different response characteristics to changes in throttle. Whether these would be potentially significant enough for you to notice, I can't say.
I would expect that the flight controller may be able to compensate, but I still recommend against using different ESCs or firmware. You should also recheck your PID gains any time you change ESCs or firmware.
Cool. Thanks, Dan! I'll try to figure out a way to do this right :-)