VelocitybodyyawSpeed() - during hover drone is getting yaw. MAVSDK-Python

[Murali-IsPagro]

Hi,

I am testing my drone using VelocityBody code, where I am taking off drone to certain height using VelocityBodyyawSpeed(0.0,0.0,-1.5,0.0) for 6 seconds and hovering for 20 seconds. But I observe drone is getting yaw .Before drone is getting armed the heading angle is 8.27 and once in air it is changing to 30+ degree.

Below I have attached the yaw data from the test.

murali@Lenovo:~/MAVSDK-Python/examples$ python3 offboard_velocity_body_test.py Waiting for drone to connect... Drone discovered! -- Initial Heading angle before arm 8.27 -- Arming -- Setting initial setpoint -- Starting offboard in here 8.27 8.17 8.120000000000001 8.14 8.23 9.78 12.84 15.4 18.46 22.240000000000002 25.72 27.98 29.05 29.23 hover 29.68 31.77 34.2 35.9 37.410000000000004 40.31 41.1 41.04 40.97 44.12 45.64 45.5 45.25 46.21 45.93 45.07 43.64 43.02 42.89 44.39 46.910000000000004 47.52 47.15 47.22 47.480000000000004 47.83 47.54 46.85 46.94 47.1 46.38 44.300000000000004 42.42 41.64 41.13 40.78 40.99 42.22 44.49 47.01 48.410000000000004 48.39 47.81 47.36 47.4 47.54 47.62 47.24 46.83 46.33 46.29 47.25 48.77 50.44 -- Stopping offboard

This is the code:

import asyncio

from mavsdk import System
from mavsdk.offboard import (OffboardError, VelocityBodyYawspeed)

async def run():
 """ Does Offboard control using velocity body coordinates. """

drone = System()
await drone.connect(system_address="serial:///dev/ttyUSB0")

print("Waiting for drone to connect...")
async for state in drone.core.connection_state():
    if state.is_connected:
        print(f"Drone discovered!")
        break

print("-- Initial Heading angle before arm")
async for gps_info in drone.telemetry.heading():
    yaw = gps_info.heading_deg
    print(yaw)
    break

print("-- Arming")
await drone.action.arm()

print("-- Setting initial setpoint")
await drone.offboard.set_velocity_body(
    VelocityBodyYawspeed(0.0, 0.0, 0.0, 0.0))

print("-- Starting offboard")
try:
    await drone.offboard.start()
except OffboardError as error:
    print(f"Starting offboard mode failed with error code: \
          {error._result.result}")
    print("-- Disarming")
    await drone.action.disarm()
    return

asyncio.ensure_future(yaw_correction(drone)) #subscribing yaw data from telemetry

print("in here")
await drone.offboard.set_velocity_body(
    VelocityBodyYawspeed(0.0, 0.0, -1.5, 0.0))
await asyncio.sleep(6)
print("hover")
await drone.offboard.set_velocity_body(
    VelocityBodyYawspeed(0.0, 0.0, 0.0, 0.0))
await asyncio.sleep(1)

for a in range(20):
    await drone.offboard.set_velocity_body(
        VelocityBodyYawspeed(0.0, 0.0, 0.0, 0.0))
    await asyncio.sleep(1)

async for gps_info in drone.telemetry.heading():
    yaw1 = gps_info.heading_deg
    print(yaw1)
    break

print("-- Stopping offboard")
try:
    await drone.offboard.stop()
except OffboardError as error:
    print(f"Stopping offboard mode failed with error code: \
          {error._result.result}")

await drone.action.land()

async def yaw_correction(drone):
    async for gps_info in drone.telemetry.heading():
        yaw = gps_info.heading_deg
        print(yaw)

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run())

[julianoes]

Ok, when you control a yawspeed, then you probably want to "close the loop" in your code, so then you control yaw by setting a yawspeed to reach it, basically a simple P controller.

[Murali-IsPagro]

Yes, I agree. But I am not giving any yaw deg/sec command in my code. But still I observe yaw. Is there any parameters I should change or it is natural for the drone to yaw slightly when VelocityBodyYawspeed() command is running without giving yaw (deg/sec)

[julianoes]

It is natural that there will be drift, and you need to control that drift by "closing the loop", e.g. by writing a controller to do that.

[Murali-IsPagro]

Thank you.