Today I performed some initial LOS test flights with my recently built Tyro129 7inch Quad. Power wise I was using a 3000mAh 4s.
In a hover everything initially appeared fine. Hover was maintained at less than 1/4 throttle. It also appeared very stable and precise on all axis. However after a short period of time the front left motor appeared to spool down resulting in the quad rolling and pitching downward and hitting the ground. On inspection nothing appeared to be hot, all four motors were cold to the touch. Without removing the battery I spooled it back up and put it into a hover again and after about 30 seconds the front left motor spooled down and again the quad hit the ground.
If I arm the quad and leave it on the ground with the motors running at idle speed I can hear a slight change in motor speed every so often. Unfortunately I didn’t have a SD card inserted for the Blackbox.
Back on the bench and with the props removed I connected up to Betaflight and when to the motors tab. I advanced the Master tab to the point all four motors were spinning slow but smoothly. I noticed that motor 4 would occasionally reverse direction for a few revolutions then switch to the correct direction. To rule flight controller issues out of the equation I changed the motor assignments but motor 4 still exhibited the same problem. I have calibrated the 4in1 ESC multiple times and switched between the oneshot and dshot options but still the same results.
In Blheli Configurator I have rolled back and forth between firmware versions (M-H-50) with no change to the symptoms. Altering the amount of demagnetisation has no effect either.
In the past I have experienced and rectified desync issues at max throttle values but this is the first time I’ve seen desync regardless of the throttle value.
If anyone has any thoughts on the matter I’m eager to hear them.