Look forward to seeing the new video then with the lighter axe.

One thing to think about though, which may or may not be a problem; you said you needed the paint tin to support the axe because the motor couldn't lift it from all the way back?
That may pose a problem when it comes to self-righting. If the motor can't lift the axe when it's a heavy hammer, it's probably not going to be able to lift 13.6kg when you've been flipped and need to turn yourself back over.

What's your gearing ratio on the weapon? Were the batteries fully charged? And are you running the motor at the voltage it will be running when the robot is complete? It may be okay, because when self-righting, the arm will be acting as a lever turning the weight about the pivot point of the axe mechanism rather than lifting a weight at the far end of the lever when firing the axe as normal, but just something to check.