Discussions

My last hexcopter crashed due to a battery "puking" before it was supposed to. I typically got 15 minute flights, and at the 11 minute mark the craft began a controlled descent into the dirt. Luckily damage was minimal. My OSD couldn't support a 4 cell pack, so I had a voltage tap on my balance connector to measure the voltage of a single cell. I believe that one of the cells in the pack had gone bad, and I just couldn't see it because I wasn't tapping that particular cell.

Since I am switching to the Pixhawk and should have full telemetry, that shouldn't be an issue anymore :D However, I am still cautious...

I was planning to set up the Pixhawk to RTL with approximately 5 min of battery left. I am of the "better safe than sorry" mentality. Using my 4S 8000 mah packs, this will be at 5280 mAh used. My concern is that if my battery is starting to go bad, and perhaps only has 6000mAh of true capacity, this will not be enough.

My current plan is to have a backup 3600 mAh battery (I have two left from a prior build) on the craft, and have it switched in via a couple of automotive relays (in paralell for redundancy). My flight mode switch will activate these relays when I hit RTL. My new setting will be RTL at approximately 2 min left (right around 7000 mAh used), and when I see this happen on my ground station I'll just flip my RTL switch (to engage the backup battery) and be sure I get home. I can also set my RTL at a particular voltage in the case that the battery is "puking." In the case that I command RTL earlier on (should be rare) I'll just switch out both packs so I always have a fresh backup installed when I fly.

This of course is all completely untested. Should work in theory, but collectively this forum has more experience than I could ever dream of, and before I get to that point in my build, I'm curious as to whether or not anyone has a better "tried and true" idea.

Also, is it possible to have the autopilot command my relay setup whenever RTL is engaged? I know how to make it such that it does when I command it, but is it possible for the autopilot to engage the bingo battery when IT engages RTL?

Thanks ahead of time for all of your ideas!