PWM override

[AhmedRejeb]

hi, my name is Ahmed, and I'm working on a Pixhawk with a raspberry board, I developed a PID tuning loop on Simulink that have as output the PWM signal for 4 motors I want to use the DroneKit -python lib to send those messages (PWMs) to the Pixhawk to control the motor but I don't know how can you help me

[peterbarker]

On Wed, 21 Jun 2017, AhmedRejeb wrote:

hi, my name is Ahmed, and I'm working on a Pixhawk with a raspberry board, I developed a PID tuning loop on Simulink that have as output the PWM signal for 4 motors I want to use the DroneKit -python lib to send those messages (PWMs) to the Pixhawk to control the motor but I don't know how can you help me

You will almost certainly find that the latencies mean flight will not be stable. Consider ArduCopter's stabilization loops happen at 400Hz - that gives you 2.5millisecondss to get data to simulink, calculate the PWM outputs and return them to ArduCopter - that's really not going to happen from a latency perspective!

Additionally, I do not believe ArduPilot has the ability to source PWM information for the motors from any external source - however, you could notionally introduce a new GUIDED mode which takes information from a newly-crafted mavlink packet which sets the relevant outputs.

I can't talk to PX4 Pro's abilities to source motor PWM externally.

One option you may have is to talk directly to a simulator; there is a clear boundary between simulators and ArduPilot - sensor data from simulator to ArduPilot, pwm outputs from ArduPilot to simulator. You may be able to use that to eliminate the autopilot altogether. ArduPilot's in-tree simulators are not the only ones with such clearly defined boundaries.

https://github.com/ArduPilot/ardupilot/blob/master/libraries/SITL/SIM_Aircraft.cpp#L325 https://github.com/ArduPilot/ardupilot/blob/master/libraries/SITL/SIM_Aircraft.h#L39

Using the ArduPilot simulator has the benefit of being able to lock-step-schedule to debug your code.

[AhmedRejeb]

@peterbarker thanks for your quick response, can you please explain to me more about this "however, you could notionally introduce a new GUIDED mode which takes information from a newly-crafted mavlink packet which sets the relevant outputs."" and for the using simulator i can't see what is this can help me if I want truly to fly my copter not just simulate

[peterbarker]

On Thu, 22 Jun 2017, AhmedRejeb wrote:

@peterbarker thanks for your quick response, can you please explain to me more about this "however, you could notionally introduce a new GUIDED mode which takes information from a newly-crafted mavlink packet which sets the relevant outputs.""

We currently have two guided modes. You could notionally add a third.

But seriously - consider the latencies involved! Do a short feasibility though experiment before getting to invested in the concept.

and for the using simulator i can't see what is this can help me if I want truly to fly my copter not just simulate

Simulating generally means less rebuilding :-)

[AhmedRejeb]

thank Mr.@peterbarker for the help. but now i have little different problems that I'm trying to solve but I can't: I'm trying to make my drone fly and to move to certain distance by overriding RC commands, but the very first thing is I'm not able to arm my copter through my script. But its printing: when i want to arm it the mavproxy like this .it work but when takeoff i have this error Can you help me with this

[peterbarker]

You need to be in guided for takeoff to work. mode guided will do the trick - straigh tafter arming.

[AhmedRejeb]

@peterbarker thanks for your quick response but it didn't work for me. this what i did, 1-Stabilize mode ->arm throttle -> takeoff 10 1- Stabilize mode ->arm throttle ->mode guided --> takeoff 10 2-mode guided ->arm throttle -> takeoff 10 and this the errors that i got:

i'm working in this code too but i can't make it work and arm my copter can you tell me what i'm doing wrong `#/usr/bin/env python

-- coding: utf-8 --

from dronekit import connect,VehicleMode,LocationGlobalRelative from pymavlink import mavutil import time

Receiving from command line

import argparse parser = argparse.ArgumentParser() parser.add_argument('--connect',help="PORT_NO") args = parser.parse_args()

Connecting to the vehicle

connection_string = args.connect print("Connecting to...% s" % connection_string) vehicle = connect(connection_string, wait_ready=True)

Function to arm and takeoff to a specified altitude

def arm_and_takeoff(aTargetAlt): print("Basic Prearm checks..dont touch!!") print("Waiting for vehicle to initialize") time.sleep(1) print("Arming Motors..")

vehicle.mode = VehicleMode("STABILIZE")

vehicle.armed = True
vehicle.flush()
    print("Is Armed:% s"% vehicle.armed)

while not vehicle.armed:
    print("Waiting for arming...Mode:% s"% vehicle.mode)
    print("Is Armed:% s"% vehicle.armed)
    vehicle.armed = True
    time.sleep(2)

print("Taking Off..")
vehicle.simple_takeOff(aTargetAlt)

while True:
    print("Altitude: ",vehicle.location.global_relative_frame.alt)
    #Break and return from function just below target altitude.
    if vehicle.location.global_relative_frame.alt>=aTargetAlt: 
        print("Reached Target Altitude..")
        break
    time.sleep(2)

vehicle.close() arm_and_takeoff(50)`

[peterbarker]

You can't arm in guided mode.

[suraj2596]

• Disable all pre-arm checks
• You either need a GPS lock or pixflow sensor. If using the pixflow sensor, configure it by referring to the dos on the official site.
• set mode LOITER
• arm safetyoff
• arm throttle
• Then immediately give takeoff 4
• To switch off the motors, arm safetyon
• Reboot the whole system again if you want to repeat.

Note: I tried it without props so I do not know the vehicle's actual; performance. Will update once I tried it out.

The same can be done using MAVROS services.

Hope this helps!