Actually yes we do. I cant find the thread but there was a guy with his picture next to a Lamborghini on the forum who flew two Turnigy Nano-Tech 9000's and one caught fire . Coincidentally, in this small world, I was doing a test flight in Las Vegas at a Vacant park. And was approached by the camop of said flight. I have been brewing up an idea that I learned from some MIT guys
Well, yes, and there was the guy filming those knuckleheads in Pennsylvania who were skeet shooting with live pigeons and got his rig shot up and landed like a crippled B-17 in an old WW2 movie. But really...that's verging on military requirements. Catastrophic failures with fire features are not on my radar (so to speak). Good place to start. I stole one of my early inventions from those guys. Err, I mean I produced a derivative work based on academic research I saw on a visit to MIT back in the late 80's.
Steve Your copter isn't light by any means. My copter with 2 QC6200's and the lighter 760 camera is 12 pounds. I tried using 2 QC8000's and thought it just was too heavy. Your IC2 temps for that weight and load is extremely good as the importance of CG is magnified with more weight. Can I ask what the temperature outside was? We talked about the Lipo isolation circuit this winter. I actually spent a lot of time thinking about it and it requires a lot more than at first glance or even at 2nd and 3rd glance AT this point I think its not feasible as you would need custom electronics made. Nothing that I can think of off the shelf would work. You absolutely need some logic control where the voltage of the lipo goes to an IC. The IC would need to be able to monitor input voltage and current and output or offer circuit isolation as needed. However the Lipo can't just go to the input of an IC because most IC's are "current limited". However at the same time the output of the logic has to able to yield the high output current supplied from the lipo. So in one way you need to isolate the current so the IC doesn't pop, but on the other hand you need to have the IC output the high current from the lipo. There are voltage regulators that are high current capacity (like the kind that are used in TV's) but they don't have much logic built into them that would be appropriate for this application. They just take a voltage source and regulate it regardless of input. A relay just switches a current source on and off. This could be handy for output isolation in case the lipo goes bad but it's not going to help the issue of current and solid state electronics needing to co-exist for this application.
The air temp was around 60°F and the humidity was on the high side (but not to the point of causing condensation issues). The house is right near the coast (as you can tell from the photos) and it's always relatively cool here. And the AUW of my bird with the 5D Mark III and two 8000 batteries is around 14.7 pounds.
Yup, but I find it to be a well-designed system, and I'm operating it within its tolerances. And while a heavy lifter is interesting, I am super intrigued by the Magic Lantern hack to get raw video out of the 5D Mark III because that'll satisfy some of my personal thirst for something like an Epic or other big camera. Certainly the frame rates of those big cameras are interesting, but I don't have a huge need for that right now, especially since I have several cameras from which I can get 1080P 60fps right now. Nothing close to a RED, but a bird in the hand...
Steve I think it speaks for well of how you have it setup because the CG has to be perfect at that weight for the BL's to be good. I know because I too have spent a tremendous amount of timing balancing the copter, and the gimbal and I'm no where near your weight. It will be interesting to see how your BL temps do in 80-85 degree weather the 5D. Since you are near sea level that probably helps a lot too.
Yeah, Steve, redundant flight control systems would be the way to go, but I think we're drawn to the LiPo as it's the first choke-point in the failure system. As you say, we really don't know how the batteries file -- does a failed battery appear as a short across the good battery or not. Using the balance leads (to respond to Shaun's point) might be interesting, but the question remains: viewed from the point of a "good" LiPo that is connected to a failed/failing LiPo, what voltages appear on the good LiPo's balance lead -- will they be dragged down as the voltages on the bad LiPo fail? We just don't know... Andy.
I mean "failure," using words from my parents, a LiPo that "needs to work harder." Anyway you slice it, whether you look at dual LiPo's or Flight Control systems, we should try and write the rules that determine when a "failure" has occurred. What are the defining traits that must co-exist or be consequent for such a failure to be said to exist? If we declare the two LiPo's (or Flight Control systems), Primary and Backup, what do we mean by a "failure." Might it be: 1. When Primary and Backup's voltage differs by more than X millivolts for more than Y milliseconds? 2. When the Primary and Backup's current differs by more than P milliamps for more than Q milliseconds? 3. and so on.... When I started to think about this, I realized that I really didn't know how to define "failure" (other than as used by Mr. and Mrs. Maller ) We also need to address the issue of how to identify with certainty whether it is the Primary or the Backup that has failed. Seems to me, as Steve points out, we first need to find the best way to define failure -- then we can figure the best way to detect it -- and then we can figure out the best way to provide a resilient fail-over response to it. Andy.
Thank you for that coherent explanation, Andy. For those of you who are still hanging on in this thread, this is precisely the reason that so many of us are always so curious to get all the details we can from crashes and other mishaps. We do not learn from success; we only learn from failure. Not sure who said that (besides me), but I'm sure not the first one to posit this. Anyway, we need to continue to gather data on the performance of these complex systems, and someday soon, maybe we can make some headway towards dramatically improving the safety, reliability, and performance of our birds!
Steve: There is a school of thought that says we might actually learn more from success than failure (see http://www.scientificamerican.com/article.cfm?id=why-success-breeds-success), but it is certainly true that we can a lot from failure if we're prepared to make the effort. But that brings us back to the formidable question: What exactly are the defining traits of a LiPo failure? Andy.