I replace them once a year on my main drone, which is about 150-200 hours of flight time or so in my case. The props are the only thing keeping the drone flying, it's like the rubber and brakes on a car, but more critical, so don't wait to see the degradation to change them; you shouldn't use them more than 200h or so.
Appart from cutting grass, hitting branches or chopping insects, the props wear on five main points, which all occur at a really slow rate:
- The edge of the blade. The air is not the void, it's full of suspended particles that will wear the edge through time, on dusty environments the degradation will be quicker.
- New blades have a bit of vertical movement around the rivet, and it increases with time as the plastic wears away with vibration and the forces applied while flying. With time, it will affect the angle at which the props rotate, acquiring a kind of "reverse umbrella" form.
- Degradation of the material due to oxidation and UV, as flights are performed on the outside. Props are quite resistant, but no plastic (or material) is immune.
- Oxidation of the rivet, specially if you fly near the sea.
- Bending of the props while the drone is carried around on the bag, or with the strap that holds the props together. The props will slowly bend and acquire a new curvature due to the pressure applied by the prop strap.
So in resume, a good-looking prop should be changed after around 200 hours or once a year, but ofc if your drone is just sitting in the bag forever, like my
Mini 2 for example, it's not worth the cost.
PS: Props with missing parts or dents should be changed asap, as the blades rotate at high rpm, so if they are not balanced the vibrations generated will stress the motor and the prop itself, which will lead to a midflight crash.
Pay attention to the props, but also, don't become a paranoid, as they are quite tough and most drones can fly with heavily degraded props.
