Are there any codes that make sure the quadrotor follows the generated trajectory? Thanks.
2 Likes
I suggest to use position instead of velocity. Using velocity you could accumulate position error.
Position references have to be given in the NED reference frame. You can use the set_position_ned() function. You can find it here:https://sdk.dronecode.org/en/api_reference/classdronecode__sdk_1_1_offboard.html#classdronecode__sdk_1_1_offboard_1a127749d168fe4e7ddb40ba4c6747bb4a
@elBarto Thank you for your advice.
There are two reasons why I don’t use this position method：
- Time-parameterized
The trajectory is generated with time ‘t’,X=f(t),Y=g(t),Z=h(t).It means that I need to reach the specific point at specific time,the position method can not assure this because the quadrotor travels with constant speed. And Vx=d(X)/d(t),Vy=d(Y)/d(t),Vz=d(Z)/d(t),Vx Vy Vz are easy to get.
2.Continuity
when the quadrotor is reaching the waypoint, there will be a short pause in which the quadrotor determines whether the waypoint has arrived. This makes the overall flight discontinuous.
I am looking for a controller that can make correction of speed according to the deviation between the current position and the trajectory to ensure the quadrotor follows the desired trajectory.
@sudo I have created a ROS node for exactly that reason.
link: https://github.com/Jaeyoung-Lim/mavros_controllers
It is based on a nonlinear geometric controller and works in offboard mode by sending body_rate commands
3 Likes
try to feed position and velocity at the same time with setpoint_raw. the px4 uses the velocity as feedforward information. this works quit good for me.
Nice work, thanks for it
@Jaeyoung-Lim The video looks excellent !! I am new in this and I am trying to run your pkg. I can run the sim environment successfully but cant run your launch file.
Terminal reports err as:
while processing /home/gmy/Firmware/launch/posix_sitl.launch:
Invalid tag: mavlink_sitl_gazebo
ROS path [0]=/opt/ros/kinetic/share/ros
ROS path [1]=/home/gmy/test_ws/src
ROS path [2]=/home/gmy/catkin_ws/src
ROS path [3]=/opt/ros/kinetic/share
ROS path [4]=/home/gmy/Firmware
Arg xml is arg default="$(find mavlink_sitl_gazebo)/worlds/empty.world" name=“world”/
I am stumbled here
@TobiasM Thank you for your advice. I tried this in Gazebo Simulation. I find that the drone tracks good in X-axis BUT seems that it doesnt work in Y-axis(I abandoned Z, Z is set to 2 ).
Below are part of the position log:
time
goal.x goal.y goal.z
real.x real.y real.z
17.350000
14.421766 0.179454 2.000000
14.201502 -0.499506 2.034843
17.400000
14.475429 0.247687 2.000000
14.244723 -0.445643 2.034098
17.450000
14.528336 0.315501 2.000000
14.313771 -0.359543 2.032773
17.500000
14.580449 0.382812 2.000000
14.347980 -0.314730 2.032230
17.550000
14.631733 0.449536 2.000000
14.416365 -0.225706 2.031084
17.600000
14.682151 0.515590 2.000000
14.459023 -0.170487 2.030164
17.650000
14.731667 0.580893 2.000000
14.526984 -0.082826 2.028497
Which launchfile are you running?
Thank you for your quick reply.
roslaunch geometric_controller sitl_trajectory_track_circle.launch
Did I miss anything ?
Could you try switching your firmware directory to ~/sec/Firmware ? unless you tried to manually set the path
@Jaeyoung-Lim
Fantastic! I have looked into your code a whole day. But I am a little confused about How to replace circular trajectory with my polynomial trajectory.
Sorry to interrup,which kind of vehicle frame is your controller base on, “十” or “X” ? ?
Hello @Jaeyoung-Lim !
I have a small query. In one of my projects, I was giving a position setpoint in simulations to track a trajectory and the quad rotor performed pretty well. Won’t this work on real system ?
Thanks much for helping everyone 
@Vrinda It would work as long as your setpoints are moving slowly. As quadrotors are a dynamical systems, it won’t be able to track high acceleration reference points.
For example, if you are moving towards a reference point and the reference point has a velocity in the opposite direction(moving towards the vehicle) If you give only the position setpoint, it will still try to accelerate towards the reference which results in huge overshoots.
1 Like