critterhunter

Those batteries will safely handle the BP21. It's amp draw is around 15 or so amps on a 7x6, 12 or 14 on an 8x4. The 12T draws close to 30 amps on a 8x6. Your packs can handle 31.5 amps so that will be pushing your packs close to the limit, but if you drop to a 7x7, 7x6, or an 8x4 or 8x5 you might get amp draw in the mid to high range (25 or more amps) that would be safer for the battery. You can try an 8x6 on it and see how hot the pack gets after a few minutes of wide open throttle. You can buy a Tower Pro 30 amp ESC to use with either motor but I'd make sure it gets good airflow and add an extra heat sink to the top of the ESC if using the 12T. Better off buying a larger ESC in the 40 to 60 amp range. I'm using the 30 amp on my 12T but I've got good airflow to it and cut off the top of the heat shrink over the heat sink and glued a little ribbed heat sink on top of that to aid cooling. These motors have 3mm shaft holes so use a bullet type prop adaptor if going direct drive. Cut the motor shaft down to the desired length as well as they are pretty long.