Creating new mixer model for Octo-H airframe

kangmin7 · February 24, 2021, 4:31pm

Hello,

I am trying to make an octo-H mixer model in ROMFS/px4mu_common/mixers according to Redirecting to latest version of document (main)

There seems to be no Multirotor mixer for the octo-H, and I failed to make one using the Summing mixers. Is there any way to make a new mixer model with different geometric configuration?

(picture of the drone crash due to wrong motor mixing btw)

Thank you, Kangmin Lee

RicardoM17 · February 26, 2021, 3:10pm

Hello @kangmin7

Have you tried creating a new mixer geometry: https://github.com/PX4/PX4-Autopilot/tree/master/src/lib/mixer/MultirotorMixer/geometries

It should be fairly simple. You can call it octa_h with the key “8h”

If you have any issues let me know, I can support you with it.

kangmin7 · February 26, 2021, 6:49pm

@RicardoM17 Thank you very much for your help!

I have made the new octo-H geometry like this

[info]
key = “8H”
description = “Generic Octacopter in H configuration”

[rotor_default]
axis = [0.0, 0.0, -1.0]
Ct = 1.0
Cm = 0.05

[[rotors]]
name = “front_right”
position = [1.08, 0.543, 0.0]
direction = “CW”

[[rotors]]
name = “rear_left”
position = [-1.08, -0.543, 0.0]
direction = “CW”

[[rotors]]
name = “mid_front_right”
position = [0.36, 0.543, 0.0]
direction = “CCW”

[[rotors]]
name = “rear_right”
position = [-1.08, 0.543, 0.0]
direction = “CCW”

[[rotors]]
name = “front_left”
position = [1.08, -0.543, 0.0]
direction = “CCW”

[[rotors]]
name = “mid_rear_left”
position = [-0.36, -0.543, 0.0]
direction = “CCW”

[[rotors]]
name = “mid_front_left”
position = [0.36, -0.543, 0.0]
direction = “CW”

[[rotors]]
name = “mid_rear_right”
position = [-0.36, 0.543, 0.0]
direction = “CW”

The only confusing part was that I had to invert the y position of the rotors in this file order to match the rotor geometry in the sdf file.

I wrote

R: 8H

in the mixer file and

. ${R}etc/init.d/rc.mc_defaults
set MAV_TYPE 14
set MIXER octo_H

in the configuration file.

I added the file names of configuration, mixer, and mixer geometry (the one you told me) to the CMakeLists.txt, but I still got the following error:

ERROR [mixer_module] mixer load failed with -1
ERROR [mixer] failed to load mixers from etc/mixers/octo_H.main.mix
ERROR [mixer] failed to load mixer
ERROR [init] Failed loading mixer: etc/mixers/octo_H.main.mix

Is there something more to do in order to use the “8H” key?

RicardoM17 · February 26, 2021, 7:09pm

does the mixer have the right name?

octo_H.main.mix

And you added both the mixer file and the new geometry to the respective CMakeLists?

geometry here:

github.com

PX4/PX4-Autopilot/blob/master/src/lib/mixer/MultirotorMixer/CMakeLists.txt#L34


# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
# OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
#
############################################################################

set(geometry_files
	dodeca_bottom_cox.toml
	dodeca_top_cox.toml
	hex_cox.toml
	hex_plus.toml
	hex_t.toml
	hex_x.toml
	octa_cox.toml
	octa_cox_wide.toml
	octa_plus.toml
	octa_x.toml

and the mixer here:

github.com

PX4/PX4-Autopilot/blob/master/ROMFS/px4fmu_common/mixers/CMakeLists.txt

############################################################################
#
#   Copyright (c) 2018 PX4 Development Team. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in
#    the documentation and/or other materials provided with the
#    distribution.
# 3. Neither the name PX4 nor the names of its contributors may be
#    used to endorse or promote products derived from this software
#    without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

This file has been truncated. show original

You said you did but just making sure.

Because if not it looks all good:

EDIT: nevermind I believe your mixer needs to be like

R: 8H 10000 10000 10000 0

Also I would change all so it’s “8h” as per PX4 standards, but it should work like that.

kangmin7 · February 28, 2021, 4:08pm

@RicardoM17 Changing “8H” to “8h” made the error to disappear!

Now I have to just change the control gains for the octocopter

Thank you!

RicardoM17 · March 1, 2021, 10:04am

no problem @kangmin7 ! Glad I could help.

Please select the comment with the solution so that this post can be closed.

pedro · April 21, 2021, 6:58am

Hi @kangmin7 and @RicardoM17,

I am facing a similar issue. I am able to compile and launch the new custom airframe and mixer when I run without ROS. But when I run Px4 from ROS this gives the following issue:

With ROS

INFO  [px4] Creating symlink /home/user/catkin_ws/src/PX4-Autopilot/build/px4_sitl_default/etc -> /home/user/.ros/etc
...
Info: found model autostart file as SYS_AUTOSTART=6013
INFO  [param] selected parameter default file eeprom/parameters_6013
[param] Loaded: eeprom/parameters_6013
INFO  [dataman] Unknown restart, data manager file './dataman' size is 11798680 bytes
INFO  [simulator] Waiting for simulator to accept connection on TCP port 4560
INFO  [simulator] Simulator connected on TCP port 4560.
INFO  [commander] LED: open /dev/led0 failed (22)
ERROR [mixer_module] mixer load failed with -1
ERROR [mixer] failed to load mixers from etc/mixers/dodeca_octo.main.mix
ERROR [mixer] failed to load mixer
ERROR  [init] Failed loading mixer: etc/mixers/dodeca_octo.main.mix

Without ROS

INFO  [px4] Creating symlink /home/user/catkin_ws/src/PX4-Autopilot/build/px4_sitl_default/etc -> /home/user/catkin_ws/src/PX4-Autopilot/build/px4_sitl_default/tmp/rootfs/etc
...
Info: found model autostart file as SYS_AUTOSTART=6013
INFO  [param] selected parameter default file eeprom/parameters_6013
[param] Loaded: eeprom/parameters_6013
INFO  [dataman] Unknown restart, data manager file './dataman' size is 11798680 bytes
INFO  [simulator] Waiting for simulator to accept connection on TCP port 4560
INFO  [simulator] Simulator connected on TCP port 4560.
INFO  [commander] LED: open /dev/led0 failed (22)
INFO  [init] Mixer: etc/mixers/dodeca_octo.main.mix on /dev/pwm_output0

I checked if the mixer file is missing in the symlink path but it is there.

This is how I am launching px4 node

<node name="sitl_$(arg ID)" pkg="px4" type="px4" output="screen" args="$(find px4)/build/px4_sitl_default/etc -s etc/init.d-posix/rcS -i $(arg ID) $(arg px4_command_arg1)">
    </node>

Any thoughts on what I might be missing?

I am also having the same issue with the rotor ordering. You said you had to mirror the rotors position in the Y-axis right ?

SOLUTION: I forgot to catkin build px4 ! ups