I have narrowed down a fly away problem with my Phantom FC40 to after market props. In GPS mode when I install after market 9.5" props the phantom flys away after it gets about a foot off the ground. This doesn't make sense to me. The standard props are 8". The 9.5" props do not hit eachother and I don't have prop guards on. I don't see how the props can interfere with the stability of the electronics. Does anyone have a clue as to why this happens?

My p2 experienced the same thing . let me guess . Carbon Fiber . Cheap ones .
No offense intended. I was curious to know if carbon fiber props would improve the maneuverability of my bird .

Purchased a set of $13.00 carbon props from e-bay . Not wise . My bird took off , responded to commands in a very jerky manner . Very different than normal. I was aware of a problem instantly . Still only 4-5 feet from the ground I attempted to maneuver back into my hand . I could see the bird shaking as if it were having  a nervous breakdown . I began to notice a loss of response to command .

She began to climb, all of this while  locked into 8 satellites . I regained control by toggling my s2 switch back and forth . It worked...for a short while . That scenario played out 4  more times before the bird rested safely in my hands . As long as the blades were spinning I kept losing and regaining control . Threw the blades in the catch all drawer never to be used again . Replaced props with stock and bird flew stellar and back into my hand . After isolating the props I began to dwell on the issue . Have not checked the Carbon Fiber  props for balance as I witnessed first hand the violent shaking . Constant rhythmic vibrations can and do cause amazing things . Cat walks at night clubs have collapsed due to large groups of people stomping their feet in rhythm  . Back decks attached to houses  have fallen for the same reason .

Knowing this, it is not too far fetched to theorize that the out of balance props created the ability to stun the IMU enough to cause strange output  . There are a couple of very small low mass objects inside of the IMU if I am not mistaken .
Because my bird is used for business and I need to keep my reputation clean I always use stock parts on my work bird . I do have a crash victim I plan on turning into a fun hot rod toy for the field .Hope this helps.

Michael Starley Posted at 2015-6-28 03:31
My p2 experienced the same thing . let me guess . Carbon Fiber . Cheap ones .
No offense intended.  ...

carbon fiber prop are much more stiffer than the phantoms props and so the phantom is more responsive so you should lower the gains in the software some people do some don't I don't and buying the cheap ones isn't a good thing ether I run maytech 9.4x4.3'' carbon fiber they run $21.95 but good props and you still gotta balance them.....

Thanx for the tips Robert . Will do when I get my play bird up and flying .

This doesn't have anything to do with aftermarket props per se, but it has something to do with the increased lift of the longer props compared to the original ones. I'm having issues with a different quad, but I have the Naza-M flight controller. I've been successfully flying Graupner 10x5 carbon fiber props for a couple of years and just experienced the same type problem when upgrading to 12" props.

As far as I can tell the Naza flight controller has default gains set for a particular prop size and weight. Deviating from this requires the gains to be adjusted, however it's not intuitive as to which gains would offset persistent climbing. Intuition would suggest BASIC GAIN > VERTICAL, but that doesn't seem to do it.

I've seen this issue reported here and elsewhere, and respondents either hate on the Naza, blame it on something unrelated like the compass or IMU. If they do hit the dartboard it's usually something vague and less than helpful, as in you have to adjust your gains after changing prop size. I'm not criticizing that answer, but think it would be tremendously helpful if someone could clue us in as to WHAT gains should be changed and in what direction when increasing prop sizes.

I also realized today, after noticing vast variations in my performance, that it is also good to adjust your gains according to  your climate . I live in Georgia . Hot and humid . If it is only warm and no humidity the air seems to be a little thinner(To TheQuad Anyway) . Tomorrow I plan on adding 10% . In theory this should bring me back to a tighter hover .

It is recommended to just stay with the Dji props.