Does anyone know what's the maximum weight that a Phantom 3 or S1000 can lift in the air without forcing the motors or having trouble flying? This is related to banners and such items

The P3 is not meant to carry additional items, although a small banner should be ok.
S1000 look here and the manual.
http://www.dji.com/product/spreading-wings-s1000-plus/info#specs

DJI-Ken Posted at 2016-1-9 02:51
The P3 is not meant to carry additional items, although a small banner should be ok.
S1000 look here ...

Thanks Ken! However, the S1000 seems stronger, how can I figure out the weight capacity of this drone?

Ign1717 Posted at 2016-1-11 11:24
Thanks Ken! However, the S1000 seems stronger, how can I figure out the weight capacity of this dr ...

Under flight parameters it has total weight and takeoff weight. That will give you the useful load.

DJI-Ken Posted at 2016-1-10 23:37
Under flight parameters it has total weight and takeoff weight. That will give you the useful load ...

The useful load being how much the drone can lift without probable damage?

You might want to look at getting one of the older model Phantom 1's on eBayor some of the other RC forum website.  There are also still lots of Phantom 2's on vendor websites.  Without the camera I suspect it could lift a decent sized banner if that is all you were wanting it to do.

Ign1717 Posted at 2016-1-11 15:59
The useful load being how much the drone can lift without probable damage?

I don't know, anytime you add a bunch of weight, the aircraft will work harder. I don't think it will cause damage, but make parts not last as long.