Hello All,

I have an Iris+ and when i fly it whith the short legs everything seems fine. When I attach the long legs and gimbal it flies fine (Climbs perfectly, turns perfectly, etc) for 4-5 mins and then it's like it decides to land on its own, even if im all the way up in throttle.

I sent my logs to 3DR and they just said "There is nothing wrong with your system, the problem is you are too high from sea level" (Which i though "what an easy way to end the conversation and say its not our fault!"). I am in mexico CIty which is about 2400mts above sea level.

What do you guys think of this? Anyone had any similar experience?


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  • i could be wrong, but from what i have been reading a lot on here about sudden altitude changes, i'd to a through check of your battery, look at your logs and see what it shows. some weak batteries or defective cells can drop voltage suddenly.

    your logs will tell you if it is a battery or something else.. the extra weight of the camera and gimbal will cause the copter to use more power as well.

    if you have another battery try it as well..see what results you get.

  • Wow! Im loving this group every minute more! Thank you so much for the information everyone!

    Amazing how much knowledge is here, i think im going to try the 10' props to see if that works.

    Thanks Again


    • Just a heads up, the Solo props are a good option for replacement 10" props.  They screw right onto the Iris motors.  Only difference is the colors are reversed (black to silver and silver to black).  Also, if you have a log file from those short flights that you could attach to this post, I would be more than happy to take a look at it and give you a little more insight into what's actually going on.  There are lots of things that affect flight time, but assuming everything is working correctly, you should be getting more than 5 minutes.

  • Daniel,

    I'd say they were correct.  The IRIS+ ThrOut is typically over 50% throttle when in it's most basic configuration; short legs, not gimbal.  When the longer legs, gimbal and camera are added, the ThOut increases proportionally.  Additionally as altitude is increased, the IRIS+ has to work harder (spin the props faster) to maintain thrust in the lower pressure (ergo lower air density), and ThrOut increased accordingly. When ThrOut approaches the 80% level, the IRIS+ begins loosing headroom to maintain stability.  Also the flight time will decrease because of the additional energy being used.  Operation at 2700 meters is (7800 feet) mostly probably nearing a limit without doing some customization of the props and battery.


  • You might want to look at this air density calculator .

    Where I live, last week it was around 40C, and I'm flying 193m above sea level with 30% relative humidity, so the density of air is 1.089 kg/m^3. In Mexico City right now it's 23C, 41% humidity, and if you're flying at 200m, that's around 2450m above sea level, so your air density is 0.877 kg/m^3. So you're getting 80% of the lift I'm getting.

    You would have to have 12 inch props on there to get the same lift I'm getting, but those won't fit (pardon for switching to imperial units). The standard props for Iris+ are 9.5/4.5, where 4.5 is related to the angle of attack of the blade. I've tried 10/4.7, those might give you up to 10% extra lift.

  • Here's a recent discussion about flying at altitude, which of course means different things to different people.

    4-5 minutes seems like an abnormally short flight time, but in Mexico City @ 7,382' there will definitely be a significant impact. I was getting about 5 minutes @ 9,000' with a loaded IRIS+ (gimbal/gopro/external GPS). I normally fly at about 4,000' and get good flight times past 12 minutes. The trick to extending times and pushing more thin air seems to be the 10" props, but I have yet to install mine.


    • I put a set of 10/4.7's on my Iris+, and it likes it! I'm at sea level, and have my radio timer set to 12 minutes. No stress on batteries. Just barely warm after 12 minutes. Long legs, GoPro on gimble, and FPV setup too.

    • Which props are you using and how are you attaching them ?

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