Slower landing speed?


When I try to auto land my F450 quad, the default landing speed is 0.7m/s, and the landing seems too fast which cause the drone flipped over. I find that the minimal MPC_LAND_SPEED can only be set to 0.6m/s. Is there a reason for this limit? Is there any way to lower the speed, for example, 0.3m/s?



Following. Having the same challenge and trying to avoid adding an IR beacon/sensor or lidar to resolve.

if you change the parameter via QGC you can always force save the value even if it’s below min or above max. Not sure if it won’t get overwritten in the firmware.

I’m curious about the reason, if I had to guess is that maybe a too slower speed will make it very hard to detect landing and also you don’t want to be hovering near the ground for too long. Ground effect can cause the drone to be unstable

@RicardoM17 You are right on the QGC setting. I haven’t tried to set lower than 0.6m/s.

I think something like 0.4m/s or 0.5m/s would be good for heavier drones. I am not sure what px4 use to detect landing, for heavier drones I had to use manual landing now.

PX4 does accept lower values than 0.6m/s if you force save it via QGC.

But there are some issues that come with a slow land speed: the ground detector is more prone to false positives and negatives. I don’t recall all the details in the land detector procedure, but there are a few things that depend on the land speed. E.g. the no vertical movement condition. If the vehicle is supposed to land slowly, it becomes more difficult to distinguish between still descending and having reached the ground.

Essentially, it works well if you land on level and soft ground. On uneven ground, we experienced the following several times: ground contact is detected when the first part of the drone (say front feet) touch the ground. The motors switch to zero thrust, the back of the drone falls down until it also hits the ground. The vertical velocity registered by the autopilot exceeds the no vertical movement condition (which was really small due to slow landing speed), the motors ramp up again, the drone levels out and landing is initiated once again, resulting in a loop that eventually leads to the feet braking (bouncing drone) unless the pilot is fast enough to take over manually.

Yet still, for us a slow land speed with the potential issues that come with it are so far the better solution than having a hard impact on every landing with 0.6m/s. All the time that the land detector works correctly, the slow landings are really smooth.

This is using default landing speed 0.7m/s. After touching the ground, the quad bounce up a few times and flipped over, and the motor did not stop, I had to use kill switch to stop it.

Do you think this bouncing is caused as you described or this is just landing too fast?

Landing too fast I think. From the sound of the video it doesn’t seem that the thrust was set to zero. If you can share the log I can say with certainty