Looking through the forum here, but also over at ardupilot.com and the Facebook group, one can see many folks who have either complained of poor flight performance of their IRIS or had crashes due to power loss towards the end of a flight.

Taking the data from IRIS and running it through eCalc.ch, one can very quickly see that IRIS is too heavy and underpowered to fly safely at the weight of IRIS + Gimbal + Tall Legs.

Therefore my recommendation: Don't fly your IRIS with Gimbal and long legs! It's not safe and you run a very high risk of crashing it! 
Flying with the short legs and GoPro but without Gimbal is OK. Although that's not what I purchased it for.

Have a look at the table below. The "Hover Throttle (Normal)" is the amount of throttle you need to give at the beginning of the flight to keep IRIS hovering. The "Hover Throttle (Low)" is the amount of throttle you need to give when the battery is down to 25% capacity. That's about when you should land. What unfortunately becomes very clear: IRIS is not suitable to be flown with that weight at any realistic air temperature or altitude. Required hover throttle is always more than 70% (making it a "very underpowered copter"; http://copter.ardupilot.com/wiki/ac_throttlemid/). But in all cases you even go beyond 80% required throttle at the end of the flight. You can't control a quadcopter anymore at that level.


If you want to reproduce these results yourself with http://www.ecalc.ch/xcoptercalc.php, here are the values used:

# of Rotors: 4
Model Weight: 1750g (incl. Drive)
Elevation: see table above
Air Temperature: see table above
Battery Cell: Custom
Configuration: 3S1P
Cell Capacity: 3500 mAh
Resistance: 0.0052 Ohm
Voltage: 3.7V
C-Rate: 30C cont, 40C max
Controller: max 20A
Motor Manufacturer: RCTimer A2830-12 (850)
Propeller: APC SlowFly SF
Diameter: 10
Pitch: 4.7
#Blades: 2

Or use this link.

What hover throttle do you require at what air temperature and field elevation? Post some logs along with air temperature of that day and field elevation.


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  • Hi all,

    first of all, I want to thank to Christian Elsen for nice blog. It was inspiring. Because I have feeling, that IRIS with gimbal and long legs is really clumsy flier, I decided to go for 4S battery with 10*3,8 props. Right now I am getting with gimbal, GoPro and FPV flight time 10+ minutes. More important is improved performance, it is like IRIS with 3S and no gimbal!

    I picked Zippy Compact 4000 mAh 4S 25C battery. In order to fit them in IRIS I  had to extend battery compartment. It's done by adding 5mm thick polyamid nut between leg and bottom plate (picture bellow). It was even possible to use same bolts, when you put them directly to bottom plate (not thru bottom shell), you will save exactly 5mm. Bottom shell is then attached by gimbal holding bolts.

    I also added 12V UBEC for powering gimbal, it's on place of front GoPro mount. I am pretty satisfied by this one.


    • Hi Tomáš,

      this is excellent feedback and great work! 

      I love the place where you mounted the UBEC. Haven't thought about that yet. I crammed mine next to the battery compartment on the opposite side of the USB port. 

      Do you have additional pointers on the polyamid nut, that you used? 

      Also, have you thought about the Multistar High Capacity 4S 5200mAh Multi-Rotor Lipo? There are mixed recommendations on this battery, but the weight vs. mAh ratio should yield pretty good flight times. 

      Last but not least: I couldn't agree more with your comment "...it is like IRIS with 3S and no gimbal!"  for the IRIS on 4S Lipos!
      I really hope 3DR will move to 4S (just like all the other vendors in that weight/size range) during their IRIS redesign.


    • Hi,

      sorry for late response, I have been really busy.

      About nut, I think, I used this one:

      3702665509?profile=originalNothing special, I was looking for something solid, light and 5mm thick. 10 pcs cost about 1,25 USD. After all, I think 6-7 mm would be better, but I am not planning to change it.

      Did you already tried Multistar 4s 5200mAh? I seems really promising. I have to check last flight logs for power consumption, but I think 20A will be enough.

      BR, Tomas

    • Iris redesign? 

      recently they started selling the arms at a discount. is this because they are coming up with a lighter replacement?


  • so how long had you had your IRIS before sending it back??


  • Christian,

    Which propellers did you end up buying? (ie which product/store?)



  • Hi

    Did you see this posted earlier..

    These lower C batteries are lighter and drain slower so may give longer life/flight?


    I may try these.


    • IRIS with 3S and that weight is still underpowered and needs extremely high hover throttle. A lower C lipo won't change that.

      If the 4S-5200mAh version (http://www.hobbyking.com/hobbyking/store/__56840__Multistar_High_Ca...) would fit into the battery bay of IRIS - which it doesn't - and you would replace the current motors with e.g. RCTimer 2830/14, you would have a decent hover throttle (around 50%) and could achieve flight times of 15-17 minutes. 

      The "trick" to long flight time of such a heavy beast are:

      • Higher propeller dimension (limited to 10" due to IRIS design)
      • Higher voltage lipo (limited to 4S due to IRIS ESC)
      • Lower KV motors with higher thrust
      • Higher capacity, lower C lipo with low weights (Limited by the battery bay size)

  • A lot of extraneous weight on the iris. Don't really need the fancy looking plastic shell. Best and lightest quads I've had were two fiber plates sandwiching the arms. Add additional decks with standoffs. Keep it light.... Weight is very expensive.
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