We’re catching up with our video archive, and I found this fun video that illustrates the kinds of non-research fun we’ve been having! A frustrating problem that took us a long time to fix, and caused us to cry out “D’oh”!
So we were about to try a new test flight, and the quadcopter was resting on the athletic fields when we usually run our test flights. I started increasing upward thrust to get off the ground, and usually the quadcopter would smoothly start lifting upward. But this time, the quadcopter instead started tilting towards the right. Only two legs would get off the ground, with the other two still on the ground. It felt as though the quadcopter would just flip over before even taking off! I pushed the throttle down, and tried gradually upward again, but the same thing happened. And it happened over and over, and each time the quacopter would rise on two legs I would bring it back down, for fear of flipping. This felt extremely unusual. Our monitors weren’t even enabled yet! This video shows what was happening, and you can hear me complaining how something is wrong:
“It’s just wind!” said Dan. “Just gun it upwards and it will get past the turbulence!” And indeed it was windy… and indeed, turbulence can be worse at ground level because the rotors are blowing wind into the ground… but still… we had lots wind before and nothing caused this kind of tilting.
I felt something was wrong, something was off. So we tried the time-tested remedy to many of our problems: reboot the quadcopter! So disconnect battery, and put it back in. This often fixes odd intermittent problems, since it resets the GPS, and all sensors, but this time, it didn’t. Same problem! We then re-calibrated the compass, and made sure the GPS was getting enough satellites. But the problem persisted. We reverted to the stable version of the software that didn’t have our changes on it, and still the same thing.
Dan said: “Look we tried everything, it all seems ok, and it was working before. It’s probably wind, just gun it upwards!” Dan is cavalier, but me, not so much. I was reluctant. But by this point, we’re all reaching our limit, and we had to try something, so I was tempted to “gun it upwards”.
But then I noticed something. The display on the controller looked a little different than usual. And then it all came together: the fine-tuning knobs! The left and right stick on most controllers have some sort of fine-tuning, which essentially allows you to set what value zero position of the stick means. This can be useful in some manual modes to fine tune things so that when your pitch/roll stick is at the zero position (where zero position means you’re just not touching it and it stays at its center), the quadcopter stays put (and if it doesn’t, there are small knobs/buttons that you can use on the controller to set the fine-tuning). It turns out in this case, someone accidentally pushed the fine-tuning knobs all the way to the right, so that the zero position really meant “go all the way to the right”. Once we fixed the fine-tuning back to normal, everything worked as before. “D’oh”!!!
Lesson 1: always check your fine-tuning!
Lesson 2: If something feels odd and wrong, be careful. We could easily have broken some propellers if we gunned it all the way up (and I really was about to do it!!!)