I built an Ft gremlin over the fall and have been flying it for the past couple of months. This week, the front right motor has been malfunctioning. When I arm the quad, all of the motors arm normally, but when I give it throttle to take off the front right motor(motor 2) stays at the same rpm as it does when it is just armed. I have crashed it a couple of times, but it continued to fly normally. I checked all of the solder connections and all of the wires are connected. I went into Betalight, to the motors tab and individually tested motor two(the motor that was giving me issues). At full throttle, it was still just at the "armed" rpm. What steps should I take to fix this problem?