OK, this is totally weird.
In Mission Planner > Initial Setup > Optional Hardware > Battery Monitor I can sit and literally watch the Measured battery voltage parameter change, and along with it Calculated voltage (calced) changes. Both numbers are going in the POSITIVE direction. Calced voltage should go NEGATIVE.
What the heck is going on?
What voltage sensing device are you using.
If you are using the Mauch Sensors, you can get jumpy and odd readings if you are using 6S or higher voltages and did not address the solder jumper issue.
If memory serves me correctly for 6S and higher you need to solder a jumper on the Mauch voltage sensor. And the voltage divider should be a number around 9.8 to 10
Sounds like a bad voltage divider, resistor going bad.
I once had a power distribution board that started giving crazy voltage readings, it had to be junked. One problem could potentially be a break in a wire or bad contact too I guess, but I would have expected those issues to give lower or zero readings.
Every voltage sensor I have ever calibrated on Arducopter does this. The Mauch are the most stable in my experience. For reference:
http://ardupilot.org/copter/docs/common-power-module-configuration-in-mission-planner.html
Older video, but still relevant if you are calibrating your own sensor:
I’ve been doing this a LONG time. I keep my battery monitors calibrated to within +/- 50mAh between logged and charged current.
It is only recently that I have seen this behavior.
I use the plain jane APM/Pixhawk battery monitors.
After each build I make a series of test hops and use the charged vs logged current reading to tweak the Bat Amps per Volt and “dial in” the sensor.
Once I get the sensor dialed in I can calculate to within a few seconds as to when my low battery fail safe will trigger. At that point I have about 20% of the battery capacity to get “home.” Typically I am back on the ground well before that, but this has saved my bacon a time or two…
Very nice! What battery voltage are you typically running? Does your work flow include monitoring MP and a calibrated meter to get dialed in?
One of the reasons I moved to the Mauch sensors was accuracy out-of-the-box, but more importantly capacity. Under certain conditions I am lifting close to 10 pounds of payload, and needed closer to 150A of capacity on the sensor (during takeoff).
I like the idea of truly “dialed in” current consumption. I don’t like to run much below 35%.