Help with cruise altitude

bovick

Well-Known Member
I've been using RVOSD for a while now and mostly have things worked out with my platforms. Recently, I changed over a spare finwing penguin to rvosd and have an issue.
Above cruise altitude + altitude limit the plane glides nicely with glide throttle in effect.
Below cruise alt + alt limit, the motor kicks on and it dives.
The problem is that even after it gets below cruse alt, it keeps diving with motor going at cruise throttle setting!
It seems to want to just keep going down.. and it basically won't RTH anymore at this point.. goes in random directions and then makes a hard turn, and random direction again.
As long as it has altitude high enough to be on glide throttle, it behaves very nicely and heads towards home (unless there is wind, as I found out in another flight :( )
Any help is appreciated.
 

ommadawn

Well-Known Member
Check to see what is happening with the vibrations when the motor kicks in.
Also, does it dive under power when you are in FBW mode? Try it at the same motor current setting as is programmed for RTH.
 
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bovick

Well-Known Member
Check to see what is happening with the vibrations when the motor kicks in.
Also, does it dive under power when you are in FBW mode? Try it at the same motor current setting as is programmed for RTH.
Thanks. I'm going check on vibrations and yes, after the rebuild (cracked fuse, damaged wings a bit) it did seem to be wanting to dive on full throttle. I launch with 80% throttle in FBW and it works great as long as I give it around 30% up elevator on launch. In level flight it seemed to want to dive on neutral elevator with 80%+ throttle.
I was hoping RVOSD would compensate and give it the needed up elevator despite throttle wanting to push it down.. motor mount angle hasn't changed, so what could be causing it to want to dive so much? I'll recheck on COG as well.. thought I had it right. Did notice that I had to adjust neutral elevator to be a bit of up elevator..
 

ommadawn

Well-Known Member
You could try increasing pitch gain. Mine is about 100. That will make the autopilot and FBW more reactive to the thrust trying to push the nose down. It sounds like the down thrust line of the motor is excessive. I guess this should be sorted out outside of anything you are doing with RVOSD in any case.
In gliding flight, when you switch in and out of FBW do you get any noticeable pitch change?
If so, it can indicate either neutrals not set correctly and saved, or AHI neutral not matching the aircrafts attitude for level flight. (and saved)
 

bovick

Well-Known Member
This is all very helpful. This airframe was flying perfectly until a recent crash and I guess the rebuild wasn't perfect apparently. The motor mount / tower area wasn't touched in the crash, but somehow the thrust angle seems to have an issue now with full throttle pushing it down.
On the most recent flight, other than CG feeling a bit behind where it should be (felt 'pitchiness'), gliding seemed to be fine, with FBW keeping it nicely level as long as motor was under 30% or so. Higher throttle started to force it down.
Back to the field to test :/
 

evox

Member
have you added lots of trim to the plane? as the autopilot does not take into account the added trim and if the gains are low it might not compensate enough?
if so maybe try centring the trims and adjust your control horns ( then adjust the cg to correct trims if fixed )
 

bovick

Well-Known Member
have you added lots of trim to the plane? as the autopilot does not take into account the added trim and if the gains are low it might not compensate enough?
if so maybe try centring the trims and adjust your control horns ( then adjust the cg to correct trims if fixed )
No, everything is pretty neutral and RVOSD has the trim saved as it should. Unfortunately, further testing lead to bad crash. GPS lost signal and RTH did not work. The GPS was even soldered on the board side.. this is getting stupid. Have 4 other fpv rigs running great on APM & Pixhawk with gps that locks within seconds and has yet to lose signal in the air.
 

evox

Member
Could the osd of been damaged from a previous crash?
have you tried increasing the altitude climb gain? i think stock is 40 try 50
 
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