I built and modified a Parallax Elev-8 quadcopter - added an APM 2.6, external GPS/compass, telemetry transceiver, and later a Tarot 2 axis gimbal and 600 mW video transmitter. But I was not happy with the flight endurance time using the stock 1050 kv motors. Wanting to improve my endurance time, I rebuilt the aircraft by replacing the motors with Tarot 4006 620kv motors, 30 A OPTO ESCs, and a UBEC to power the gimbal & vtx. Here's a pic of the finished product:
The aircraft is powered by a 4s 6000 mAh lipo. Based on a thrust test I saw a guy do with the same motor/propeller combination, I expected flights over over 20 minutes. But a test flight today under almost calm air, produced a flight time, mostly hovering in Loiter mode, of only 3 1/2 minutes before the voltage failsafe kicked in.
I looked at the log file and saw this voltage profile:
My question is this: is the large drop upon takeoff normal? Perhaps I need to replace the battery? I've had it awhile, using it on my Tarot hexcopter. When I charged it up, the charger read 16.56 V when it said it was full. My multimeter says the battery is at 15 volts now.
Any insights would be appreciated!