Oleg I do agree that a A7075 shaft is very good, but it will all depend on the length of your shaft : TC3 AND TC4 use a 175mm A6061 main shaft that bends a lot when I put a NOVAK 3.5R ON IT (let alone the HV4.5R THAT HAVE ONE OF MY TC4's running); the NTC3 USE a A6061 162mm main shaft that somewhat bends if you put a .12 Picco tuned in there. If the A7075 shaft you use is less than 140mm and hollow(very important) than it will be good for whatever motor you put in ,including a 2.5R at 7.4V(40C). Precisely how long is the shaft? If so, is it hollow?