Drone Response to /mavros/setpoint_velocity/cmd_vel_unstamped

alfa budiman

I got my drone setup with MAVROS and Q Ground Control and it appears to be responding when I publish to /mavros/setpoint_velocity/cmd_vel_unstamped

However, there's some issues with the drone's response. I've only tested it moving purely vertically up and it is unstable / doesn't respond right away.

For publishing to the topic I made my own ros node (velocity_publisher.py) that lets me input the desired velocity in the form (vx,vy,vz,wz). This input corresponds to the movement in m/s (or rad/s) in the drone's forwards (vx), left (vy), and up (vz) directions, with wz corresponding to rotation along the z (up) axis. I confirmed that I am publishing correctly when using rostopic echo. I confirm that these directions are correct; I have moved the VOXL FLight deck itself powered up but un-attached to the drone while observing rostopic echo /mavros/local_position/velocity_body.

For testing, my steps were as follows:
1 - Open QGround Control and 3 terminals. On each of the terminals I ssh to the drone.
2 - On terminal 1 I run MAVROS as per your instructions here: https://docs.modalai.com/mavros/
3 - On terminal 2, I run velocity_publisher.py
4 - On terminal 3, I arm the drone using rosservice call /mavros/cmd/arming True
5 - On terminal 2 I input my desired command velocity.

Here are my issues:
1 - I publish (0,0,vz,0). The drone doesn't move until (approx) vz>0.5. This is an issue if I want the drone to move at a speed less than 0.5 m/s.

2 - When the drone is moving it is unstable and drifts undesirably. While I input (0,0,vz,0), I only want it to move straight up. However, it clearly has very noticeable lateral motion.

3 - Some motors are sluggish to start when arming.

Some theories as to the cause of the issue:
1 - Improperly calibrated ESCs. They were calibrated as per the steps here: https://docs.modalai.com/flight-core-pwm-esc-calibration/
Though, I did change the PWM_MAIN_MIN / PWM_MAIN_MAX parameters on QGRoundControl. I'll reset them to factory defaults and re-calibrate everything.

2 - Improperly calibrated sensors, especially gyroscope. I don't think this is an issue I calibrated on Q Ground control using a wired connection. But same as # 1, I can reset the parameters on Q Ground Control and re-calibrate everything,

3 - Misaligned propellers. I can re-assemble the mounts for the motors to ensure each of them are properly aligned.

I will be resetting the parameters and recalibrating everything on the VOXL Flight deck as well as re-assembling the propeller mounts. What else should I look at?

Chad Sweet

Have you gone through the basic drone bring up process? Can you fly in manual mode? What about position mode? If those aren't working properly it is to difficult to debug through higher level behaviors.

alfa budiman

@Chad-Sweet
What is the "basic drone bring up process"?

I can fly it in manual mode, it's not easy to fly, but I felt like its more due to my skill level as its behavior from virtual joystick was somewhat similar to when I tried virtual joystick with your RB5 drone.

It does drift noticeably. I think this drift is excessive but again, I'm not sure if it's an issue with the drone or my skill level using virtual joystick.

It didn't seem to respond to virtual joystick inputs in position mode but I didn't extensively enough test that mode. I'll test that mode again and see what happens.