I was landing the phantom 4 and was just 3 inches from the ground when for some reason it jerked sideways, probably from ground effect.  When that happened it hit a wooden planter on the side and 2 propellers came to rest.  I received the motor obstructed error message.  I tested the drone by hovering and it seemed to fly fine.  My question is should I dump these propellars and use new one?  I checked them and it seems ok but I don't want to take any chances.  What would you guys do?

Many will say ditch them as a precaution, but if they look OK after close inspection I'd continue to use them. Depends on how much of a risk-taker you are.
They are actually made of a quite strong yet flexible plastic. Look for dings in the edge which may throw them out of balance, and inspect with a light on the other side to see if there are any hair-line fractures in the plastic. Hey, I've accidentally pruned bushes with one set, and they are still perfect...

Someone here lost a tip from a prop so cut off the other side to match/balance and kept flying. I would not recommend that but think that you should be OK if there is no physical damage.

If no damage to prop, go ahead flying. The motor cut off is a new feature that priorities safety against human tissue damage over damage to aircraft. The P series aircraft are reasonably crash resistant anyway.

I've put the old propellers aside just for now.  I guess what I'm more concerned with is did it do any damage to the motors?  I've spun the motors and one has noticeable clicks.  The other three motor's clicking is not as pronounced.  This drone was a refurbished unit from DJI and I don't know if this was the case when I first got it since I was not paying attention to it.  Is there any definite way to check the motors to see whether they're within specs?

ibuyufo Posted at 2017-4-5 21:58
I've put the old propellers aside just for now.  I guess what I'm more concerned with is did it do any damage to the motors?  I've spun the motors and one has noticeable clicks.  The other three motor's clicking is not as pronounced.  This drone was a refurbished unit from DJI and I don't know if this was the case when I first got it since I was not paying attention to it.  Is there any definite way to check the motors to see whether they're within specs?

Only thing I can suggest is to leave the props off and start the motors up (but don't try to take off as it wont be happy). Then listen for any variations in the 'whirr'. If it's a clear sound without any hiccups, I'd take it outside for a hover test to see if it is stable in the air.

If it topples over on landing and the propellers hit the ground while not under power then I don't think there is anything to worry about, also if they hit something soft or light weight like the end of a tree branch, but hitting a very hard surface (concrete?) under full power will put a lot more stress on them.  Given the reasonably cheap price of propellers and the large cost of the drone, I think it is sensible to replace them even if they seem OK.

If you are replacing propellers due to hitting something hard then it is also sensible to replace the plastic mounts.  They are probably OK, but some people have had the mounts suffer stress cracks several flights after a hard hit.  

The plastic mounts should have protected the motors, no need to worry about them unless the rest of the aircraft is also destroyed.

Nigel_ Posted at 2017-4-6 02:42
If it topples over on landing and the propellers hit the ground while not under power then I don't think there is anything to worry about, also if they hit something soft or light weight like the end of a tree branch, but hitting a very hard surface (concrete?) under full power will put a lot more stress on them.  Given the reasonably cheap price of propellers and the large cost of the drone, I think it is sensible to replace them even if they seem OK.

If you are replacing propellers due to hitting something hard then it is also sensible to replace the plastic mounts.  They are probably OK, but some people have had the mounts suffer stress cracks several flights after a hard hit.  

Thankfully the P4 never toppled over!  The propellers just hit against the wooden planter and just stopped spinning.  I turned it off as quickly as I could which was probably like 3 seconds after I got over the shock.