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Alta X - I'm in!

Discussion in 'ALTA X' started by Tom Comet, Sep 11, 2019.

  1. Tom Comet

    Tom Comet Member

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    We just put our $$ down and bought into this all new ultra heavy lift, zero redundancy quad copter concept. I believe! And I also believe that if anyone can do it, Freefly can!

    In my 6 years flying drones I have seen two heavy lift octocopter cine machines go down while I was at the controls and neither time was it pilot error. Neither time would it have helped one bit to have more "spinny bits" in the mix either.

    The first crash was due to charging LIPOs in a cold environment and having them show full charge when that was not the case - electrons act strangely in the cold and we learned that lesson <30 seconds into the flight! We knew to keep bats warm but our charging station was in the cold - Bad!

    The second terrible day took place a few years later when a saboteur launched a rock off the roof of a bank tower inside the perimeter of a closed and secure film set downtown and that rock sheered off both props on one boom of our coaxial and down she came right ate the feet of the entire cast and crew. We got VERY lucky that day!

    Both experiences were horrific and days I would not wish on my worst enemy but both were amazing learning and growing experiences that we have survived benefited from indirectly.

    Really, when it comes down to it most of all our combined drone flying success really still relies on not having a single point failure, EVER! I feel that it is a better idea to focus on ALL the critical components in the system and make bloody sure that they are the very best that they can be. From the Pilot on down through the training, OPs, planning, security, maintenance, and, finally, the hardware. If any of this stuffs up bad things will happen! Build it right, maintain it, fly well, follow your OPs and best practices and buy the very best and all will be well. Welcome to aviation!

    We live in this day and age of risk aversion and an overzealous eye for perceived "safety". We are strapping parachutes on extremely well engineered systems with a proven track record of non-failure. These "safety systems" add complexity, weight and tax these well engineered systems to the point where they are probably more likely to fail.

    Flying these amazing complex robots is a difficult and risky thing to do. It takes a certain kind of person to do it well. We must take it very seriously if we are to succeed and I believe Freefly is on the right track with the new Alta X. Only time will tell for sure and I am looking forward to seeing how it goes. I will keep you posted.

    To be continued...
     
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  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Wow, Tom! A saboteur? I've not heard that story before.

    Did you get anywhere with the high altitude research?

    Cheers
    Andy

    Forensic Software & sUAV / Drone Analyst : Photographer : Videographer : Pilot (Portland, Oregon, USA): Trees=2, Ground=1, Props=11. :(
    The Ground Is The Limitâ„¢
    ---------- Forensic Drone Analyst : Forensic sUAV Analyst : Forensic Unmanned Aircraft Analyst : Forensic Drone Expert
     
  3. Tom Comet

    Tom Comet Member

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    Yes, a very bad but equally lucky day indeed. Here is the video -

    They never found the guy even though it was a closed set and the building was a secure bank tower on a weekend. My guess is bored security guard having a smoke on the roof throwing or kicking a stone over the edge for "fun".
     
  4. Tom Comet

    Tom Comet Member

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    Yes, still working on all this as the project is a GO. We have an aerodynamic physicist on the case but all anyone can really tell us is this is "extremely experimental". I found a guy who flew an Inspire 2 to 19,800' with high altitude props and he claims it flew remarkably well so that is encouraging. We will be shooting some of this on I2 / X7s but we really need to get a stripped down RED Helium up to 15-16,000' if at all possible.

    Freefly does not recommend changing prop size/pitch on their ALTA 8 as it can cause "desynching" where the motor/ESC timing goes out of sync and the motor literally screams to a halt or acts completely irrationally. That sounds terrifying and NOT something I want to experience on a drone with no redundancy! I haven't got an answer about the desynching AX in this regard. Those are very specialized props so not even sure if bigger / steeper pitch would be available. Our thought is desynching could occur at altitude due to prop overspeed from less oxygen molecules to push against.

    This is all proving to be more difficult due to the fact that the AX probably won't even arrive until a mere couple of days before departure for our first foray to the Himalayas (if it gets here prior to departure time at all).

    So all in all it is a pretty normal mission and everything is proceeding swimingly!
     
  5. Wayne Mann

    Wayne Mann Member

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    Man, that was a really bad day and thanks for sharing. I can't help but feel that under the same circumstances with a flat octo, assuming the rock only took out one prop assembly, you would have been able to get the machine down in one piece and at least be able to save the camera and lens. I do not care so much about the machine, but about the rental equipment on board and the safety of the crew. Not necessarily in that order. I had a motor failure on a flat octo, with a Mini on board and was able to prevent damage to the camera system. That is why I am so pro redundancy when it come to heavy lift drones.

    For your shoot you may consider using an M5 with a stripped down Red and small lens and no FIZ control. I have flown Minis and Reds a lot in my M5 gimbals. I have flown Minis with the 4.5 pound Hawk V-Lite Anamorphic lens several times in my modified M5. The motors and controllers are the same as in the M10 and M15. Just a smaller cage. The M5 can use a small 4 cell lipo for power or you can use a 4000 mah 4S pack to power the camera and gimbal to save even more weight.

    Wayne Mann
    www.helicamhighdefmedia.com
     
  6. Tom Comet

    Tom Comet Member

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    Yes, an conventional onto probably would have survived but who would ever even imagine that potential threat? Well, I do now...

    Yes, we are looking at M5s due to their weight savings for sure.
     
  7. Robert Keyes

    Robert Keyes New Member

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    This sounds extremely interesting - do you mind sharing your research? I've also been doing some high altitude research for a potential upcoming shoot to Denali
     
  8. Tom Comet

    Tom Comet Member

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    Well, I can't take credit for this research at all as I quite school in grade 10 BUT I do have a very smart guy on my team and he has some very small contacts. This is what they came up with RE ALTA 8 at Altitude. these guys are aeronautical engineers first and drone guys second so there is not a lot of hands on experience with the ALTA 8 but some great data...

    -----

    I've used the performance data from page 107 of the Alta 8 manual to extrapolate to higher altitudes. I decided to try to use a thrust coefficient type of calculation to back calculate their assumed available thrust - I've called this the weight coefficient. This seems to be the right approach as the weight coefficient is very much constant across all of the range of published performance data, except for small differences at a few low altitude data points, which I think is because they artificially limited the maximum mass to 18.1 kg for some reason.

    The first page of the attached spreadsheet is processing of the performance data and calculating the average weight coefficient across of the altitude and temperature scenarios from their table. The average weight coefficient is approximately 0.03763. I would assume that they've limited the take-off mass to preserve the prescribed thrust-to-weight ratio at MTOW of 1.85:1 shown in the spec page. This would imply a thrust coefficient of 0.06962, but that's not immediately important until we start comparing to alternate propellers.

    The second page starts by using altitude and temperature as inputs to calculate the ambient air density. Using the weight coefficient from the first page we can calculate the maximum take-off weight if we assume 6300 RPM which is given in the spec sheet. Results are shown in the spreadsheet but I've summarized in the plot below as well. Unfortunately there's no scenario which leads to an MTOW greater than 15.8 kg.

    One option to make it work are to accept that the drone will have a lower thrust-to-weight ratio than the 1.85 likely assumed for the performance data. 15.8 / 1.85 = 8.5 kg -> meaning that the service ceiling of the drone is approximately the altitude where the MTOW is about 8.5 as the thrust-to-weight ratio drops to about 1:1. That translates to a service ceiling of maybe 7000-7500m. Since the summit is obviously above that then weight will need to be reduced or the propellers changed. Since there are no official high-altitude propellers for the Alta 8 and it apparently misbehaves with aftermarket propellers I'm not exactly sure what to suggest for this.

    If we can find a way to make APC props work with the ESCs (is there some sort of recalibration that can be done?) then there are some options. There are a few options at 18 inches (18x12WE, 18x12E, 18x10E) and we can refer to the UIUC database to get an idea of static thrust coefficient. Remember from above we suspect the thrust coefficient of the alta props is around 0.069 - that's based on the MTOW and the thrust-to-weight published. The 18x12E APC props have a P/D ratio of 0.66 so we should check the UIUC database for other props that have the same ratio - presumably they use the same profile and scale up the size. The UIUC database has data for the 9x6E props and shows a thrust coefficient of 0.11 to 0.12 (link). Using these props could help generate extra thrust in low density conditions. Obviously they would burn out the motors at low altitudes so they would be special purpose for high-altitude applications. I'm not 100% sure how to check if the torque of these props exceeds the limits of the motors but that's something to be conscious of if we decide to move down that path. Another propeller option would be to use a 3 blade Alta propeller with the same profile (or hack and slash and make one?).

    ----

    Just trying to dig up their spreadsheet now...
     
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