Basic Mixer Question

[13brv3]

Greetings,

I've read through some of the threads that talk about mixer settings, but I haven't found that anyone really seems to agree on how this should be set up. For now, I have one basic question, and hopefully we can agree on the correct answer.

Say I have a copter with 4 arms, in a + orientation. Each arm has two motors, but not coaxial. One motor is 10 inches from the center, and the other motor is 20 inches from the center. I'm hoping we can agree that one of these will get a mixer setting of 100% for pitch or roll, and the other will get 50%. The question is which motor gets 100%?

I see two ways of looking at this, which makes it confusing. On one hand, the motor that's farther away will generate more torque due to the extra leverage, so if you look at torque, the inner motor would be 100%, and the outer would be 50%.

On the other hand, the inner motor will generate a much faster rotation speed, so if the mixer is concerned with the rotation speed, then the outer motor would get 100% and the inner would get 50%.

Is there a definitive answer for which motor gets 100% and which would get 50%? From the other threads, I'm sure people will suggest 33/66, 25/50, or other combinations of mixer values for various reasons, but mainly I would like to start with the simple question of whether the inner or outer motor gets the higher number.

Thanks,
Rusty

[epyonxero]

Im also curious what "100" means with regards to mixer settings. Because conventional quad mixers always seems to use +/- 100 I have been operating with the assumption that the value in the mixer is telling the controller how much influence each motor has on the pitch/roll response. So starting with the outermost motors with the longest moment arm these are assigned 100% as the max and all others are assigned a fraction of that equal to the ratio of their distance from the axis of rotation over the max motor distance on that axis.

But from the motor mixer thread it kind of sounds like higher mixer numbers increase the response from the motors which would be the opposite of what I posted above. Another issue im wondering about is whether collinear and coaxial motors should be treated as independent or set to work together.

[chschmid]

Gents

It is a topic with a lot of opinions.
For (symmetric) quads your mix numbers are always the same.
The values can be somewhere between 50 and 100. Have a look at Angels thread .

For more than 4 motors, the geometrical arrangement gives you a good point to start.
e.g. Hexa X config, the roll axis has between 50 and 100 for the left and right arm, and between 25 and 50 for the front and rear arm ect. You can calculate the vectors with the angle of the arm given.
Keep the signs in mind for the right quadrant.

In the discussion we started to use the term 25/50, 33/66, 50/100 mixing just as a shortening.

If you keep Angels findings and this in mind, you will have a nice flying machine.

Cheers
Christof

[13brv3]

Thanks for the reply, but I've read through most of that already, and noticed the varying opinions. I'm confident that I can figure out the proper percentage based on the geometry of the copter, but I have to know for a fact whether the higher number goes to the motor that's closer to the center, or the one that's farther away. That's really all I'm asking.

Cheers,
Rusty

[chschmid]

Hi Rusty

Here are some samples with drawings.


Look at it in different way. Its not the distance from the center, it is the vector to the axis.
The motor perpendicular to an axis has lets say 100%, the one at 60° to front or to the back of it has a lower percentage cos(60) = 0.5 * (the percentage of the perpendicular) and so on.
That's where the term 50/25 or 66/33 from comes from.

Is that understandable?

Cheers
Christof

[Kisssys]

[13brv3]

[Kisssys]

[epyonxero]

For whats its worth I fired up MATLAB and used this method (http://paparazzi.enac.fr/wiki/RotorcraftMixing) to calculate the values for a Y6 and ended up getting 50% for pitch and roll on the four front motors. Seems to fly better than the defaults.

[LPR]

If you use lower motor mix values you can have a copter fly better. The reason is because you have vibration problems and lower settings help hide it. You will have less redundancy because the motors can not compensate as well if you lose a motor or prop.

Larry