bicopter mixer profile, pitch for left motor reversed; no throttle response

[johnty]

i'm building a brushed bicopter using a naze32 board and have managed to bridge the PWM outputs on the board to drive the two servos. some things i've noticed:

• first problem: by default the pitch contribution to the LEFT servo appears to be reversed. after changing this line the pitch contribution to -100, as in:

{ SERVO_BICOPTER_LEFT, INPUT_STABILIZED_PITCH, -100, 0, 0, 100, 0 },

makes both servos tilt the same (i hope correct?*) way when pitching forwards. (I could have it backwards, in which case the RIGHT servo should be flipped, but this is minor...)

*edit: turns out its the other way round :) so left should be 100 and right is -100.

• second problem: despite what looks like a correct mmix:

# mixer
Mixer: BI

# mmix
mmix 0  1.000  1.000  0.000  0.000
mmix 1  1.000 -1.000  0.000  0.000

I get no throttle response at all. The motors are wired up fine: motors tab works; arming spins them up as well.

Any idea where I should be looking?

This is what it looked like last night on CF1.x, where I was able to get throttle but wrong servo mix :)

This is what it looks like right now with the change to servos.c, with the servos going the same direction with pitch, but still no throttle.

Thanks!

update: ok, figured out most of it. turns out the BI preset is valid for the smix, but mmix is undefined due to the USE_UNCOMMON_MIXERS definition. so now i can at least get it to move predictably. still not sure how I would make custom smix's to work through the CLI, as i'm basically hardcoding the smix preset right now... (i also did briefly try to set the parameter for servo to "true" for the CUSTOM setting but doesn't look like it did anything.

turns out tuning a bicopter is a bit more difficult compared to a quad, as the trim has such a huge effect with no counter-balancing props ;) also the crappy servos probably don't help either...

here's a short clip of it crawling on the ground, at least somewhat predictably ;)

[johnty]

so, some TL;DR points of discussion:

1. may be more consistent to apply the USE_UNCOMMON_MIXERS check on both smix and mmix settings?
2. is there actually a bug for custom smix/mmix's, or did i not use them correctly? based on my experimentation i couldn't find any profile (including CUSTOMAIRPLANE, etc which should have enabled servos) that allows arbitrary mmix and smix's to be applied correctly.
3. in terms of the actual bicopter preset, i think the flipped pitch may be good to have since the most obvious (default?) way would be to mount servos with horns facing outwards, especially considering yaw is already making this assumption and operating correctly.

[mikeller]

Point 1 makes good sense, I think that is an oversight from when USE_UNCOMMON_MIXERS were implemented. Also, note that non-quad support and testing is very limited in Betaflight, so 'there be dragons'. ;-)

[mikeller]

@johnty: Has this been solved?

[johnty]

sorry its been a while, but as far as i can tell these changes have been merged in. 1 and 3 seem to be in the current code, and 2.), if i can recall, was actually due to my misunderstanding of how the logical servo slots worked. so probably good to close this :)

thanks for checking up on this!

[mikeller]

All good, just cleaning up. ;-)