Problem with battery failsafe

Ground Control Software Mission Planner
1

Hi everyone! I have a feeling I have something misconfigured in mission planner specific to my battery failsafe.

Specs:
Six 920 Kv motors
Six 30 amp ESC’s
One 3S 6500 Mah venom battery
One pixhawk flight controller
Flight time ~= 5min
Battery failsafe = 10.2
Starting voltage @ battery = 12.60
Starting voltage @ mission planner = 12.44
Ending voltage @ mission planner = 11.79

Problem:
I have mission planner to trigger the failsafe at 10.2 V. About five minutes into flying I am given the failsafe alarm because the battery has hit or gone below 10.2 V. Which seems strange to me.

After landing, my battery bounces back up to 11.79.

To add to the issue, after balance charging my lipo to exactly 12.60 I connect it to my model, connect telemetry via usb on mission planner which shows a starting voltage of 12.44.

Not only that but mission planners HUD shows 87% left.

So I guess my question is multi-part

  1. Why am I seeing a difference in voltage of .15 volts?
  2. Is there some configuration setting that I might be overlooking?
  3. Why is my lipo voltage jumping so drasticly after landing?
  4. Do I really have 87% battery left as indicated by the HUD?
2

Kristopher,

Have you calibrated the battery?

In mission planner, under initial set up, you should see battery (or something like that) under required hardware.

Here’s a link to the wiki http://ardupilot.org/copter/docs/common-power-module-configuration-in-mission-planner.html.

It’s not uncommon for the battery voltage to increase when when the load is reduced (landing)

Dave

3

A lot also depends on your battery and it’s internal resistance.

All batteries aren’t created equal, and you could be seeing a large voltage drop under load if it’s a cheaper end battery.

Posting a log would help so we could see the performance of battery during flight.
What is the C rating of the battery?
When you recharge how many mA are you putting back in?
When you enter the measured voltage in the Battery Monitor tab on Mission Planner are you also adding an Amp use?

4

Thanks guys, I’ll have to post the logs here in a bit. Below are the answers to the questions you’ve asked. I’ve also included more details about my second flight after making recommended changes.

Had I calibrated the battery?

I thought I had, but I must have done something wrong. My power module was listed as “other”. I changed it to 3DR, set the voltage to 12.6 and changed my battery failsafe to 9.6 (knowing I’m just keeping it a couple feet off the ground for testing)

What is the C rating of the battery?

20C

How many mah’s was the pack charged with after flight 1
1904 Mah

When I entered the measured voltage am I also adding amp use?

I don’t think so

AB Test results:

Flight 1

Stabilize mode
"Other" power module
Failsafe set @ 10.2
Total flight time ~= 5 minutes
Mah charged into battery after flight: 1904mah

Flight 2

Stabilize mode
3dr power module
Failsafe set @ 9.6
Total flight time from arm to disarm = 14 minutes, 33 seconds
Mah charged into battery after flight: 2301mah

Additional Flight 2 Details

Voltage measured at battery, preflight: 12.60v
Voltage measured by mission planner prior to arming: 12.45v
Voltage and capacity remaining (near end of flight) measurements:9.6v@51%
Failsafe triggered measurements: 9.55v@49%
Landed measurements: 9.41v@56%
Lipo bounce back within seconds of disarm: 11.01v@46%
Mah charged after flight 12.43v@4340 (still charging)

5

sounds like either a battery or connector problem.
is anything getting hot?

6

Nothing is hot, I’ve just received a brand new 5500mah battery. I was also thinking it might be a battery problem. I’ll be doing some AB testing between the two, today.