Some drones currently have several sensors that will move away from an object if it is within a certain distance from it. Obstacle avoidance seems nice, but I want to know at what speeds it becomes ineffective, for I highly doubt that a drone flying 20 miles per hour will have time to detect something like a tree (or anything else really) and stop, not to mention that its momentum might "push" it forward even after the motors stop spinning the direction it was heading. What is the distance that the sensors begin to "repel" against an obstacle? I currently don't own any drones with sensors on the sides, front, and/or back, yet I plan to buy one, so I really wish to know more about this. If there's anything wrong I said or anything that can help me understand this topic better, please let me know. Thanks

Obstacle avoidance seems nice, but I want to know at what speeds it becomes ineffective, for I highly doubt that a drone flying 20 miles per hour will have time to detect something like a tree.
DJI's design engineers are very smart and are ahead of your ideas about the OA system.
With OA disabled, the drone flies faster than with OA to allow for sensor range and braking time.

Labroides Posted at 9-2 03:21
Obstacle avoidance seems nice, but I want to know at what speeds it becomes ineffective, for I highly doubt that a drone flying 20 miles per hour will have time to detect something like a tree.
DJI's design engineers are very smart and are ahead of your ideas about the OA system.
With OA disabled, the drone flies faster than with OA to allow for sensor range and braking time.

So it literally can't crash into anything when OA is enabled? What's the max speed when it's on for the different modes?

AJ356 Posted at 9-2 03:44
So it literally can't crash into anything when OA is enabled? What's the max speed when it's on for the different modes?

So it literally can't crash into anything when OA is enabled?
No ... sensors aren't magic and can be fooled in some situations.
There are limitations to the sensors and the conditions under which they are effective.
You can read about that in the manual for each model.

Depending on OA sensors to save your drone if you fly in dodgy conditions is unwise.

Well, it depends on what it encounters and in what conditions.
Some objects are not recognized. But it is unpredictable which ones never will.

Are there any objects/areas known to cause problems with OA? Some manuals say to avoid snow, bodies of water,  and some other things. Not sure if it will be ok inside something like a cave that might be too dark

Think of it this way. OA is very nice to have. Treat it as a luxury and plan to not need it so much if you can. I have found that a lot of factors can compromise the system.

AJ356 Posted at 9-2 09:38
Are there any objects/areas known to cause problems with OA? Some manuals say to avoid snow, bodies of water,  and some other things. Not sure if it will be ok inside something like a cave that might be too dark

The manual's explanation is sketchy and concentrates on the downward sensors, rather than the forward obstacle avoidance sensors.
The comments about flying over water/snow etc are all related to the downward facing VPS sensors ability to provide horizontal position holding in the absence of GPS, rather than obstacle avoidance.

In general the obstacle avoidance sensors require good lighting to see obstacles and even in good lighting they can have difficulty with small obstacles, such as narrow branches or wires.

Thank you @GaryDoug and @Labroides for your responses. I'll keep all of this in mind when flying