Smooth turns in survey waypoint missions

Hello. I posted about this in the QGroundControl thread, but it was suggested that I bring it up in the firmware thread. If I’m not in the correct thread, please direct me to where I should go.

I’m trying to figure out how to make the turnarounds in a survey waypoint mission be smooth instead of the default 90° turns. In other words, the default turns look like " Π " and I’d like them to look like " U ".

I need this because I fly a LiDAR sensor on a large quadcopter (Freefly Alta X). Part of LiDAR data processing requires the rectification of the trajectory based on GNSS and IMU data. To get the best results, it is very important that the trajectory be smooth (i.e. no large accelerations from speeding up/slowing down or sharp turns). It has to be smooth even in areas where you don’t care about the data. So, I can’t simply have the turns occur somewhere beyond my area of interest (unless I got very far, but that’s not ideal either).

So, the default 90° turn behavior actually impacts our LiDAR point cloud quality noticeably. Is there any parameter(s) I can change to make the turns smoother? Ideally, it would be a continuous semi-circle, but anything that’s more smooth than the default behavior would help.

Hi @Arktix ,
You can try to increase the waypoint acceptance radius (https://dev.px4.io/master/en/advanced/parameter_reference.html#NAV_ACC_RAD).
To have a smoother turn you can reduce the maximum yaw rate (https://dev.px4.io/master/en/advanced/parameter_reference.html#MPC_YAWRAUTO_MAX )
and maybe try to use a different yaw mode (https://dev.px4.io/master/en/advanced/parameter_reference.html#MPC_YAW_MODE : along trajectory) or even lock the yaw during the whole flight (e.g.: always North).
For the rest, you can also tune other parameters of the trajectory generator itself: https://docs.px4.io/master/en/config_mc/mc_jerk_limited_type_trajectory.html

Have fun with your AltaX!

Hi Bresch,

Thanks for your reply. I’ll play around with some of these parameters and see if it get’s me what I’m looking for. I had thought of waypoint acceptance radius, I figured that would just make the aircraft stop at each waypoint with less X/Y precision (i.e. could stop far short/long/left/right of the waypoint). I haven’t actually tried it though, so I’ll give it a go.

I can’t change the yaw mode because the LiDAR sensor has to always be facing/moving forward. It can’t slide sideways or backwards. This will degrade the quality of the trajectory and, ultimately, the point cloud accuracy.

I’ll play around with the parameters you suggested and see where it gets me. Thanks!

I’m revisiting this topic now that I’ve tested the parameter changes suggested by @bresch. Changing these parameters did help make the turns less robotic and “jerky”–particularly at the corners of the " Π "-- but the aircraft still follows the " Π " shape overall. What’s even more problematic is that it still comes to a brief stop at the corners. I’m still trying to figure out how to make it perform a nice continuous U-turn. In other words, I’d like it to do the turnarounds as a banking curve, like an airplane would. Does anyone have any other suggestions for how to achieve this?

Hello Arktix, I would like to contact you to find out if you have found a solution to the problem of gentle turns in a waypoint mission, because I have the same problem and cannot find a solution.
Thank you :clin d’œil:

Hi lolosoniuc. I haven’t found an ideal solution yet. I have played around with various parameters to make the standard Π turn a little more smooth and not so jarring at the corners, but I have not been able to make a continuous banked turn, like an airplane. At this point, I’m still just flying out beyond my LiDAR collection extents to do the turns. I think a true continuous banked turn is going to require some kind of custom waypoint type and I haven’t had a chance to look into how to do that yet. Sorry I can’t be more helpful.

Hi, I am at the very start of my journey into finding the best/most economical way to build a multi-rotor that will need the same smooth waypoint flying as you do. I want to build to fly a small blackmagic camera and have come across references in Urdu pilot where it describes the spline curve it can plot through waypoints, this might be useful for you to follow up on. https://ardupilot.org/copter/docs/mission-command-list.html.