I was just flying my drone when I crashed in some tall grass and there are now a bunch of grass bits all over the drone. How can I clean the drone without damaging it?
I have found that the simplest and probably one of the safest ways is to use a compressor (alternatively a compressed air can will probably work), to lightly blow away the dirt. This works especially well if you just want to get rid of grass straws or similar.
If you want to more thoroughly clean something Joshua Bardwell has a video on how to clean a motor, and if you want to clean a PCB or other electronics, alcohol > 90% and some kind of brush or cotton swab works. And finally, if it's the frame you want clean, soap and hot water works.
I've got a paintbrush in my flight kit which I use for removing chunks of mud/grass from my quads so I can keep flying on the day.
If they get really dirty, I use a toothbrush dipped in alcohol once I get home.
If they are really bad, I pull them apart and go over each part with the toothbrush and alcohol.
I've had success cleaning grass from drones using a damp cloth (just water.) You shouldn't need chemicals to get grass splatters off if they are fresh, but if you do use them then try it on an inconspicuous part first in case it does cause discolouration.
Make sure the battery is removed to prevent damage should any electronics get too wet, and let the aircraft dry thoroughly before powering back up.
For non-electronic parts (frame, camera case etc.) I'm using just those "cotton ear cleaning sticks" and plain water. If you just wet the dirty spot, wait a minute until the water softens the dirt and then you can just easily wipe it off.
And for electronics I would use same technique but use alcohol like other answers recommend.