That NTM motor may not have enough low speed torque to get the bar spinning up in a competitive time and will likely get dangerously hot. The NTM motors are good quality but I would try to use something with a wider diameter and closer to 4KW peak power (or at least leave room for an upgrade).

The main concern to me are the aluminium arms supporting the weapon - With the energy on tap they will very likely bend on the first full speed impact. Try to increase the wall thickness and diameter as much as you can.