A2 Custom Mixer

[JLO]

In an effort to find the best performance out of a custom build coax 8 copter I have been looking at ways to increase its efficiency performance, the copter flies nice but the bottom motors are slightly warmer than the top my understanding is that the bottom motor works a little harder than the top because the bottom motors get disturbed air from the top motor, the top motor gets clean air so if I can find an adjustment where the bottom motors work the same as the top motors in theory, I may increase my current flight times.
I have try smaller prop on the top but I did not felt any difference, I read that decreasing 5% or 10% Thrust to the top motors in the mixer would even them out and save on battery, I think I understand the concept of what to do in the mixer but the A2 mixer has 0% digits in all the boxes, what number should I put in the mixer?, would be 95% or 5% down in the throttle column for motors 1,2,3,4 only?.
I try the other day to see what happened, and to understand how the mixer works a random number like 50% on one motor, I was expecting all the motors to spin normal except for the one I change, but what happened, or at least it felt to me, that by changing 1 motor the preset idle speed got higher and all motors spin at the same rate ??? so here it is I stumble into a knowledge wall with this, it would be great if a few bright minds out there that actually know about the DJI advance custom Mixer topic and that would like to share could pitch in, in order advance our collective knowledge
thank you all

@Bartman;
sugested to start a new thread on this topic

Im currently Fling a Custom Coaxial 8 Cinestar Frame
Dji A2 controler w GPS
U5 motors
TM 40A Esc
16x TM CF props top and bottom
2x 10k 6s Lipos
Gimbal
I get about 8.5 minutes w 20% left
Futaba
AUW 23 LBS

 

[Bartman]

Hi @JLO;

The mixer table is there so you can identify motors individually by position and how they contribute to each of the control axisis's (whatever the plural of Axis is!)

I've set up custom mixers using Mikrokopter but from what I can tell the DJI A2 mixer table works similarly.

As far as throttle is concerned, if all of the motors are going to contribute to lift then they should all be assigned 100%

From there it's a matter of figuring out which direction for each control axis is positive and which is negative.

For example, pitching forward I'd guess will be +100% for motors located aft of the CG and -100% for motors forward of the CG

Rolling left I'd guess will be +100% for motors right of the CG and -100% for motors left of the CG.

For Roll and Pitch motors will either be +100% or -100% depending on which side of the CG they are for any given control axis.

For Yaw, motors will be +100% or -1005 depending on the direction of rotation of the motors so all of the clockwise will be + and the counterclockwise will be negative, or vice versa, you just have to figure out which way it is using trial and error.

Get it all set up and then post a screen shot here and we'll look at it. After that you just anchor the heli to your table or the ground and fire it up to check if you're getting the control response you're expecting.

Hope that helps.
Bart

 

[Bartman]

Reading your first post again, I've used higher pitch props on the bottoms with very good results. To do this I've had all of the tops spinning clockwise and all of the bottoms spinning counterclockwise using 14x5's on top and 14x7's on the bottom or similar depending on which of my heli's we're talking about.

 

[Bartman]

@JLO any luck?

 

[JLO]

HI bart hmmm on the mixer it makes sense that all the motors should be 100% so to keep a balance of trust forces in a simetrical copter, the idea of decreasing like 5% the power of the top motors came from another forum that Im trying to find but in the mean time take a look at this 2

http://forum.freeflysystems.com/index.php?threads/x8-dja-a2-conf.4763/

http://wiki.dji.com/en/index.php/Customize_Motor_Mixer

 

[henrysj]

I've wanted to give this a go too. I'm using a Herk board and A2 and use this custom setup which might help you... (motor's 1 - 4 are top) I'm not sure if these would all need to be dropped down to 95% to get the result you are after
View attachment 22750

 

[Bartman]

that's basically it Henry, give it a try, if any of the controls are reversed just swap the +'s for -'s and vice versa

 

[Area21]

I fly a SkyJib X4 and the manufactures Aeronavics recommend to get the best flight times to run the same propellers on all 8 motors and to run the lower motors 7% faster. So my question is shall I just add 7% to the bottom motors on the A2 Throttle settings and not change the Yew Pitch and Roll settings ?

 

[smartaerials]

I was running the top motors at 95% but I got 1 minut less flight time..
Anybody succeeding in time bonus from changing the % at mixer?

 

[Bartman]

i've heard the 7% faster rule of thumb before but I actually add 1 to 2 inches of pitch on the lower motors for the same effect at the same speeds.

If I'm using 15x6 on top I'd use 15x7 or x8 on the bottom