Don't attach a disc directly to a motor. It may work fine in the antweight class (I'm no expert on this) but unless your motor has a decent 10mm plus diameter shaft you are going to snap it, especially in a FBS. You need to machine a seperate shaft and then using a belt and pulley transfer the energy to the disc shaft.

even in a kilo machine I can see the energy and forces involved getting silly and believe me when it comes to FBS you do not want to screw around.