Forward speed slows when descending

In an AUTO mode, I have WP NAV SPEED set to “1600” . I needed the quad to fly higher in order to clear a big hill - from 100M to 350M. Going UP, the craft maintained its speed. However, when going DOWN, it slowed down to about half speed. When it got back down to 100M (which was another waypoint), it suddenly accelerated back to normal speed. The log files show that the pitch was never near the limit and decreased during the descent.

So why did it slow down its forward motion while descending? There was no speed command embedded in the mission.


The issue is probably because WPNAV_SPEED_DN probably limited how quickly the vehicle could descend. The default is only 1.5m/s so raising this may help.

The reason this value is so low is that many vehicles become unstable when descending straight down at a higher speed. Of course they may be able to attach higher downward speeds if they are also travelling forward and we have an issue on the to-do list to somehow allow this.

Anyway, maybe for now you can either increase the parameter or add a DO_CHANGE_SPEED command to increase it just before the downward leg. The first parameter of the DO_CHANGE_SPEED command allows you to specify whether you want to change the horizontal speed (set the first field to “0”), upward speed (set to “1”) or downward speed (set to “0”).

Thanks! It “hit” me yesterday that might be the reason. I’ll change that parameter and run the same mission. I think it is a good idea to add a feature that allows faster descents if moving horizontally vs. straight down.

1 Like