Y6 Yaw imbalance

[SuperSharpShooter]

I have a yaw imbalance on my Y6. If I have all motors straight, my LOG_MOT_YAW will be centered around 100, and some motors are working much harder than others. I have been managing it with about a 3 degree anticlockwise tilt on the rear pair of motors. This way the motors end up around the same heat after a flight. I'm not sure if the motor tilt is impacting the handling and efficiency. I haven't tested it, but I would expect there to be a worse yaw imbalance if I was running the same props top and bottom.

On all motors I have APC 12x3.8s on top, and 12x6E's on bottom, with the front top two motors running clockwise, and the tail pair have the rotation reversed.



Has anyone has success using the mixing table to fix up a coaxial yaw imbalance? If I reduced the yaw to say 90 for motors 1 & 3, is this likely to have any other negative effects? Is this even the right approach?

I'll try straightening the motors and give this mix a try tomorrow when it is light and take a look at the logs.

Cheers

[kinderkram]

Hi Shooter,
you should try the Y6 mix from our QGC where the rear motors move the same direction as the front motors:

Y6-hexa-coax.jpg (33.11 KiB) Viewed 16179 times

Use QGC v.1.2.1 for it...

[SuperSharpShooter]

I think that having all 3 props on the top level rotating the same way would cause even more of a yaw imbalance. I will give it a go though anyway and see. Changing the mixing table today didn't do much.

[epyonxero]

My Y6 used the same motor layout as yours and also has a yaw imbalance. Tilting the rear motor evened things out but I havent tried changing the mixer.

[SuperSharpShooter]

The Y6 is no more. Rebuilt it as a hexa X. Hopefully it will start to perform the way it should now!

[Max]

Glenn, sorry to hear you gave up on the Y6! But I do hope you like your hexa better.

There will be an emergency update to the recommended Y6 mixing table... Looks like the arducopter version is better indeed, or whoever came up with that originally. That's also the mix I used on my original Y6, and is available somewhere in the d-loads area, but I had given into people's claims that it didn't matter and simplified it for the "official" version. Anyway, I finished rebuilding my Y6 (new Rusty UAP1/16mm frame), finally, and this is the first thing I checked and tuned. Props are all same type/size/pitch (11x5 carbon APC-E knockoffs) The graphics should speak for the rest...

hexa_coax_(Y6)_old.png (7.41 KiB) Viewed 16117 times

hexa_coax_(Y6).png (7.35 KiB) Viewed 16117 times

BTW those are from the maiden and then the 2nd flight of new build... I haven't even re-calibrated to the new frame (yet). The 2nd flight was obviously more "active" as you can tell...

I will be trying higher pitch props on the bottom, just to see how that goes, because obviously the lower motors are loosing a bit of efficiency. On that first flight, the lower motors were just a bit warmer to the touch after the flight, but felt equally warm (or cool, rather) after the 2nd, so I'm pretty happy with that already.

-Max

[Kisssys]

Max,

It would sure be interesting to know how it does with 5 engines running. It would seem it should out perform a standard hexa but not sure if yaw will be the limiting factor on how heavy it can fly with one engine out.

[Max]

It sure would be interesting... I just busted a prop, dumb-thumbing it, so maybe now's a good time to find out...

-Max

[SuperSharpShooter]

Hi Max,

What pushed me over the edge yesterday was my LOG_MOT_YAW saturating (i think) after I tilted the rear motor pair back to where I had it previously, which resulted in the Y6 losing yaw control and pretty much just spinning in either direction before I put it down. It always felt a bit like it was fighting itself, and the battery use was pretty terrible, so I figured I'd convert it. It will stay in this config for the foreseeable future due to the amount of work required to reconfigure it. I've never broken or lost an APC prop in flight, and am using good quality motors, so I'm not sure the redundant coax setup was worth it for the problems it caused.

I'm still not entirely sold on the combination of props I used. The bottom 12x6E props weigh 29g vs 18g for the 12x3.8SFs, so it may have taken longer for the bottom props to adjust their speed. Also the decreased cross sectional area of the 12x6's compared to the 12x3.8s may have given less lift (?), and somewhat cancelled out the effect of the increased pitch.

What I found with that prop combo, without the tilted rear pair, was the front top motors would spin slower than the top ones (~1475 vs 1575pwm), and in the rear pair, the top motor would spin quicker (~1575), and the bottom, much slower (~1425). Tilting the rear pair mostly evened the outputs, but then somehow caused the loss of yaw control that I experienced.

I think that maybe if the bottom prop was the same type and shape but with an increased pitch, then it would perform better than my setup did without having to tilt the rears.

Here's a shot of my log from the loss of yaw control yesterday. Now that the rain's finally stopped here I'll give the new hex a test flight. Fingers crossed!

[SuperSharpShooter]

Just tested the new setup, and it handles much better. Performance is the closest to perfect it's been. There's still some movement in position hold, but generally less than 30cm laterally. Batteries come down barely warm vs very warm with the Y6 setup.