Hello Everyone,
We are using thunder 240A 12S T-motor ESC for our dodeca copter. I have set these parameters
MOT_PWM_MIN 982
MOT_PWM_MAX 2130
MOT_SPIN_ARM 0.02
MOT_SPIN_MAX 0.95
ESCs are not calibrating however the navigation LED is showing that flight controller sending the calibration commands.
Waiting for your response
Update to ArduCopter 4.3.6
Post a .bin log file.
It looks like T-Motor Thunder ESC is an up-rated Flame ESC 
of limited availability, possibly old stock.
This is the extent of the specifications, apart from the title which indicates battery cells and amps
Weight 0.750 g
which appears to be wrong anyway 
0.75 grams?? that is a microscopic ESC.
I would be highly suspicious of something in this high range that has no information available.
That could be OK for unbranded cheap ESCs for your small play-around quad where damage will be negligible and easily repaired.
Anyway, the T-Motor ESCs that are in that range require the following settings:
MOT_PWM_MIN,1100
MOT_PWM_MAX,1940
and they cant be calibrated
and careful consideration and testing of
MOT_SPIN_ARM
MOT_SPIN_MIN
MOT_THST_EXPO
MissionPlanner motor test is your friend
And definitely update to latest stable firmware too.
I have been tested with MOT_PWM_MIN,982
MOT_PWM_MAX,2082, ESCs are calibrated & working.
I wouldnt believe or trust that.
All those T-Motor ESCs use
MOT_PWM_MIN,1100
MOT_PWM_MAX,1940
I would definitely set that PWM range, and you can even run the calibration in case you want to be sure.
Only their consumer-grade ordinary T-Motor Air ESCs can be calibrated to any PWM range. They have new BLHELI based ESCs too, but that’s not relevant here.