I am currently driving a (small) conveyor belt with a modified 5V servo for continuous rotation:

This works fine. The load isn't heavy BTW, the belt runs empty most of the time. However, after 10-15 mins the servo runs hot and starts to smoke. Probably a modified servo cannot run continuously for a long time? Or did I simply have a bad servo?
So what should I do now?
Use a stepper motor like this one?
Or a gear motor?
Or something else (not too expensive and using 5V)?

