T-Motor MN2806 KV650 with Arducopter 4.2.x

Well that sucks, no telemetry output on these ESCs according to the manual

You will need to disable Low RPM Power Protect regardless of the dire warnings or the ESC will never operate with anything but quad-racer style high kv motors. Doing this is very common, and in fact required for all but small racing style quads.

Instead use these HNTOCH settings for now, and they can be adjusted after test flights
INS_HNTCH_ENABLE,1 ← set this then refresh params to see the rest
INS_HNTCH_MODE,1
INS_HNTCH_REF,0.2
INS_HNTCH_FREQ,80
INS_HNTCH_BW,40
INS_HNTCH_ATT,40
INS_LOG_BAT_MASK,7
INS_LOG_BAT_OPT,0