i have recently built a quad ,i am using the HK multi-rotor flight controller v3 in X configuration ,today when i connected the battery one motor i.e the back right motor started spinning the other motors start later and at different values of throttle stick,please help me ,will upload a video soon
regards
rohan

Have you calibrated the ESC,s ?

Not performing ESC calibration the mistake that every first timers do (even i did the same )

do the esc calibration one by one or else all in one time that will help u rotate all motors together

A simple jugaad like this can be made to calibrate esc all at once. I cant expect a newbie to do it but in principle its easy and hassle free

Just in case if anyone needs know to how to make one of those ^^^
+,- is shared with 1st pin to power the Rx.

Got those pins from here

i calibrated the esc but that did not work well ,but after some time it did work and the motors are running at the same time.