OK, I’ll share one that’s a little long and involved but brought with it a lot of new lessons learned and old lessons reminded. This is going back to about 2019
I do a lot of waypoint missions in my work, both in mapping and “progress” videos showing progress on sites where I’ll fly the same route many times over months or longer and edit the footage into a time lapse.
I had just bought the original DJI Smart Controller as I was looking for something that was a little brighter in the Australian sun and was testing Litchi on it and trying to decide whether the Amazon method was best or the method where you side load google services and use the regular google playstore version of Litchi was better.
So I made up a nice long waypoint mission, never more than about 3000ft away from take off point so as to be able to work LOS but about 7km start to finish with lots of changes of camera angles, height etc. You know, a good workout. As I often do when testing I plotted the mission along and off the coast a little so as to minimise risk to the public.
On the day I grabbed the smart controller and the
Mavic 2 Zoom I had elected to test with (my lucky drone lol) went to the location, started the smart controller, loaded Litchi and the mission and sent her on her way. About 5 minutes in and at about 1km distance I had a loss of connection, I still don’t know why. Although there was a large 50KW shore based radar array near by I’d flown there before without issue but R.F. Interference is as good a guess as any I suppose.
I wasn’t panicked, it was on the coast with flat terrain so nothing to run into and I knew that all being equal at the worst the drone would complete the mission and RTH shortly but I was of course perturbed as no one likes to lose the link right? So I commenced all the usual measures, realigned the antennas, made sure I was facing the right direction, climbed on the back of the ute (pickup for my U.S. cousins) for extra height … nope still no go, so I restarted the controller and app once again to no avail. By this time the bird had still not returned home and I was 15 minutes or more into the flight and was starting to contemplate my first drone loss.
Finally I restarted the Smart Controller yet again and this time opened up the standard GO4 app simply because I had tried everything else and after a few minutes *bingo* I had a connection. The video link was marginal but the control link was there. The drone was 875m away and at almost 900ft AGL
, I thought this strange as the maximum height of the waypoint mission was 350ft but I do set my maximum height to 1000ft because I do a lot of flight in mountainous terrain where I may be 7 or 800ft above take off point at times but only 100ft above terrain so it was possible it had climbed to that height, I’ll get to why in a minute.
So, I regained connection just in time to hear “battery critically low, drone landing” or similar. When I looked the aircraft was showing 8%. Being an Australian I started working through various vernacular for excrement in a loud voice. The problem here was not only was I 875m away but also 600m out to sea. I jammed the cyclic stick hard up to prevent the drone descending and headed for shore post haste. After a few moments I started to wash off height so as not to have too far to drop once I got over land as I knew every minute flight time would count.
I crossed the shore at about 100ft and by this time was showing 0% and I was no longer able to maintain height even with full stick up and it was coming down at the full rate. I got her across the trees lining the shore and the power lines and lined her up with the only open space being the yard of a beach side holiday home. The drone flared when the downward sensors detected the ground and the last view I had was of the kindly but startled face of an elderly lady peering out from her backdoor some distance from where I put down about 475m from where I was standing then it went blank.
With some help from the last recorded position and an hours driving around I was able to sheepishly recover the aircraft. The elderly lady was quite gracious about it all, not so much her daughter who gave me “the rounds of the kitchen” for frightening her old mother lol. I visited again the next day with flowers and chocolates for both and was invited to stay for lunch so I guess public relations were ok at the end.
So, on to the pointy end. First what I learned/relearned and secondly what I found had actually happened after looking at the logs.
I learned
1. The original smart controller with only 4gb of RAM and quite a modest processor is a bit marginal when you start side loading other services and apps. You only have to see “out of memory error” 30 or 40 times in the log to realise you’re stretching the friendship. It’s not that it’s terrible, it just has is limits.
2. Just because you don’t get interference with one controller device doesn’t mean it will hold true for another.
3. Some of your settings are stored on the drone, some are set in the software and loaded on each flight. If you change controller devices, best check *all* settings. It seems simple in hind sight but I missed it at the time and I’ve been flying in one way or another since 1990 or so.
I relearned (I say relearned because I already knew this and had taken it into account, or at least so I thought)
1. “Smart return to home” in the settings is not smart enough to realise that the aircraft uses more battery outward bound into a headwind than homeward bound with a tailwind and may abort a flight that you actually have plenty of battery for. You should probably disable this for waypoint missions where you are sure of the validity of your flight plan.
2. Obstacle avoidance is prone to false trigger in particular light conditions especially where the sun is lower and you are flying over water. Again, disable it during waypoint missions if you are sure you have a safe flight plan.
What actually happened.
This was my first waypoint mission with Litchi and the Smart Controller. Although I had gone through the Litchi settings I hadn’t looked closely enough to realise that “smart return to home” and “obstacle avoidance” which I habitually leave “off” had defaulted back to “on” with the change of controller device.
The drone was sent off on the mission and as specified before for reason unknown for sure lost connection. At some time during the flight while I was doing the “reset controller and app dance” and while flying into the wind the logs show that smart return to home had decided there was insufficient battery at the current rate of consumption and initiated RTH in a straight line as it does which meant over water and not hugging the coast which would have avoided what happened next.
Once over water due to the sun being lowish and reflecting off the water surface obstacle avoidance triggered causing the drone to half briefly, climb until the perceived obstacle disappeared and then continue a few meters before false triggering again…. and again and… well, logs show this happened over 20 times the net result being that by the time I regained connection the drone had climbed 500 feet but only travelled towards home about 80m and burned off about 15 minutes battery life in the process.
So, there is my closest call. I know I learned from it. If you feel it has value for others feel free to use it.
Congratulations to those who read my short novel.
Regards
Ari
