I recently upgraded my six-rotor UAV. In order to improve flight efficiency, I specially refitted larger blades. But when it was installed, I tested it and found a series of problems. Firstly, the electric power is very hot, and secondly, it is obvious that the thrust of propeller is getting smaller and smaller. Can someone tell me why?
If the ONLY thing you changed in the upgrade, was the size of the propellers, it may be they are too large for the motors. What voltage, motor, ESC, and props are you using and how much is the total weight of the UAV? Can you put the original (smaller) props back on and see if you still have the heat problem?
If the props are too large for the motor, the torque required to spin them at a given rpm, is more than the motor can produce. When the motor is overloaded it will draw more amps (amps produce heat) but still not be able to produce more torque. The more amps they draw, the hotter things will get. IF the props are too large for the motor it will not be able to spin the props as fast as at it could the smaller props and since the speed (rpm) is lower the thrust will be lower.
Your motor and prop combo didn't match. I use a lot of large blades on multirotor, the are indeed very efficient but the most important thing is to make sure the motor KV value and torque must match the prop blades requirements. High KV motor (fast RPM) with smaller blades suits best, low KV (slow but high torque) work best with bigger blades...its a similar concept applied to R/C car/truck when try to spin bigger or smaller wheel or gear ratio on particular motor. I even fitted bigger blades 4 blade on my FPV plane running on 700KV brushless. Manufacturer always stated on their motor specification on max limit prop size it could support, so check your motor specification.
Motor heating reasons are many, maybe heat dissipation is not good, or the wire voltage is too high. But if this condition is after the blade replacement, it should be motor and blade do not match.
Generally speaking, it is difficult for ordinary players to configure high performance powerplants themselves. Therefore, it is more convenient to directly buy a complete set of power devices, like the Skylle power system kit I bought before, which have been tested by professional technicians.