I was on a survey job for the Sacramento Kings new arena and I discovered a few good tips.
• Set your RTL at %30 of battery drain.
• Carry good electrical tape
• Buy a backup Iris+
• Get a lens guard for your GoPro.
I decided to allow my unit drain to 20% and RTL. I was 60m up and only around 100m away. The Droid lady said "Low battery, returning to launch" Sounds good to me. As it's decending I notice I'm well off the mark and headed into oncoming traffic. It's a tight quarters job and you gotta be ready. I begin to nudge it over the K rail and I hear the motors begin to decelerate. I hit hard left and, well watch the quick video.
The gimbal plate cracked in half but I was able to use electrical tape to finish the job. I had a Mobius on there for shits and giggles and the GoPro was the survey unit. You'll see it fly. Gotta hand it to GoPro. That's one tough unit. I did have a CPL filter on there, but if you can use a cheap 3D printed hood, do it. That filter saved my lens.
So if you're ever unsure out there. Trust your gut and RTL.
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One point in all of this that does not seem to have been made is the importance of calibrating your voltage and current monitor - there is plenty of info on how to do this. I do not own an Iris but I believe it comes with a cheap lipo charger. Does it show maH put back into a pack? In any event, if it is a cheap charger, and you are serious about flying UAVs, junk it and buy a good one. Every time you discharge a battery to 20% or so you should check that the mah put back is close enough to what MP says you used. This can be made quite accurate by calibrating it to be accurate at hover current levels - power modules are notoriously non-linear so calibrating them to be accurate at lower throttle will not do. A digital power meter (only $30) is essential for this.
A good charger, as has been pointed out, also tells you when internal resistance is high and lipo condition is questionable.
If you are using FrSky and a Taranis, get an S Port multi cell monitor (only $20) and set your TX to squawk when your lowest cell hits 3.7V. Also use the timer feature on your TX. When the flight times start decreasing then you know your batteries are reaching end of life. I really feel if your TX is not giving you an individual cell readout of voltage, and you have not set it to alarm at 3.6/3.7V, and you are relying solely on combined cell readout in MP, you do not get early indication of individual cell problems. Honestly, I calibrate the 3DR voltage and current monitor so i can have useful dataflash logging but I always rely on my FrSky cell monitor readings on my TX while in flight.
I think battery failsafes are a last resort. Like the "Pull Up" squawk on a jetliner, you never want to trigger one. I have mine set to Land at a voltage lower than I would ever fly it (unless I am flying over water). If you really want to preserve your expensive tool then you really need to get multi cell voltage monitoring and know your batteries performance through testing and calibration. Quite apart from anything else good quality lipos themselves are expensive and easy to damage.
Just my 2 cents.
Good stuff Marc
I fly relatively expensive equipment around expensive houses and tall trees so I cannot really rely on GPS modes or RTL etc. A level of paranoia about batteries, care of batteries, and monitoring is the order of the day! The advice I have gleaned on this site has saved me much heartache so one tries to take a minute to share.
I could have added - get a Teensy 3.1 and get Mavlink telemtry on your TX but that is probably OTT and overly technical for most people who may not be using openTX anyway.
I should have added a link to this though. The best $18 I ever spent.
There are a couple of good lessons in this post.
First is you cannot rely on a battery percentage remaining figure or a Mah consumed/remaining figure in order to determine when to land. The only reliable way to handle this is through using the pack voltage and experience with the aircraft. Flying a 4S pack you should plan on having your craft on the ground when you reach 14.2 (10.6 on 3S) volts under load. This means if you are a ways out, or down wind from your location you will need to know when to start back in order to have enough batter remaining to make it. These numbers are conservative and will help your batteries last a long time. I have some flight packs that have over 250 cycles on them and they are in great shape., but I charge slow and don't discharge them to the limit. As a side note, make sure you store your batteries at storage voltage in the refrigerator. Never fully charged and never let them get hot.
The reason you can't rely on Battery % or Mah consumed is without knowing the Internal resistance (IR) of each cell and the pack IR you have no way of knowing how many Mah you have consumed. As a LIPO pack ages it starts to build resistance in the individual cells. The higher this resistance grows the more of your Mah you lose to resistance and heat as you are drawing from the pack. Most chargers will calculate the IR and show you what it is per cell. Here is a breakdown of what the resistance tells you:
MilliOhms per cell
0-2 MOhms New high quality pack
2-10 MOhms been through some charge cycles and still in good shape
10-20 MOhms You are noticing reduced flight times as the batteries are aging.
20+ MOhms The pack should be retired as it is no longer reliable
I make it a point to check and note the IR of all of my cells before and after each flight because that tells me right away what condition the battery is in.
The original poster probably damaged that pack he was flying to the point it will no longer fly as long and may no longer be reliable.
The second lesson is NEVER NEVER NEVER rely on any type of RTH as a flight strategy. This will bite you right in the rump if you do it. The reason I disable all power related RTH functions is I have seen this feature cost people their machines in a number of cases. Also sometimes if you have to increase your amperage draw momentarily it can cause the voltage to sag into the falisafe range and cause a failsafe that is unnecessary or unwanted.
The OP made mention of "I bought an autonomous robot". No you didn't. The auto systems on these craft are nice, but every time you send one up you have a lot of responsibility riding on your shoulders. 99% of all problems caused by UAS are pilot error either during the flight of pre-flight.
The OP also said something about testing failsafe measures. This should be done regularly, but only when you are out in areas where there is no danger of the craft coming into contact with people, property and roads with traffic on them. You should make sure to never allow your craft to enter into or stay in any type of RTH or failsafe mode. Never allow your craft to land autonomously if there as any chance of other people or property could possibly be injured or damaged.
If you are in areas where people are present manually take off and land your craft. If your mission requires some way point flying then use this functionality judiciously and don't lose focus on your system and solely rely on the flight management system. Be ready at a seconds notice to retake control of the craft and manually land it.
Sorry if I sound lie I am on the soapbox, but learning these lessons the hard way is expensive and can cause you tremendous amounts of liability.
The "Autonomous Robot" was in response to the car analogy. When I program this drone I expect it to operate as I tell it. I, of course, know that it means that it will try to hit the waypoints programmed, nothing else. The RTL (RTH?) is not my strategy. I take off in auto and land manually. Now if 10.6v has a correlation to Mah that would be a good number to have; unless that is also constantly changing or unreliable. Again, there was no danger for people, just my wallet. The surveys have to be precise and I ain't that good. I know now that to give a large buffer in regards to battery life and will be cutting mission areas accordingly. I, ignorantly, thought that it would take into account distance from operator in regards to the RTL. Reality is that it just ran low and attempted to RTL. I learned a lot. This forum in invaluable. Thank you all for your interest and advice.
For safety's sake expect it to make regular mistakes.
It doesn't have a correlation. If you are running Minim OSD you can configure it to give you pack voltage along with Mah and battery%. Frankly I would remove battery % from my OSD because there is no way it can be accurate. Mah gives you some idea of how much you have consumed and how much is left, but this is not accurate because of the IR that was mentioned earlier.
I am not meaning to chastise you, but if someone in the oncoming traffic thinks your Iris is heading toward them, gets distracted and has a wreck, you are facing an uninsured financial catastrophe. In today's litigious society someone looking up at your machine trips, falls and is injured expect to foot the bill for the injury plus the four years of therapy and lost wages because they hurt their neck.
I use autonomous flight and a S100 for surveys, I understand. I'm just saying if your craft is in autonomous mode your should be extremely uneasy and waiting for disaster at any moment. Not relaxed, chatting with those around you figuring if there is a problem the autopilot will solve it.
As far as your Orthography goes....
Use your Sx260 with one of these Let the Pixhawk fire the camera. Then use Pix4D to make your own Orthographic image to give to your clients. Pix4D will allow you to geotag the photographs with the pixhawk log file. I think you can also do it on a timed script as well.
Will this work? (with the link you sent)
It was descending as expected (very slowly) but off the mark. It's when I took over is when it lost enough power to start to drop. 10 feet of the ground. Potentially a car could have ran over it but the construction area there is 25 mph. There were no cars coming at the time. I plead the 5th!!!
+1 (Super useful and great summary.)
My only question is if those IR ranges are correct for the Iris/Iris+ batteries (3S 5100)?
Those IR ranges should be good for high current flight batteries in the 35C range. I am not familiar with the batteries that are sold with the IRIS, but they should be good.
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