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New to forum. Vtail problem

Robrotor

Junior Member
#1
Well I maidened my vtail and doing fine...some slow circuits and such when I tried a quick forward and back pitch movement and the copter wouldn't stop oscillating front to back. I didn't have time to switch out of self level mode but did cut the throttle to try to minimize the impact. Broke one front boom and motor mount and one rear motor mount. All props and motors are ok. But what would have caused the copter to pitch back and forth uncontrollably like that? Any help is appreciated. Robert
 

rcspaceflight

creator of virtual planes
#2
I shouldn't be answering because I've never flown any multicopters, but I believe you have one of the gains set too high. It's over correcting it's self. I don't remember which gain does what. But someone will come along and answer. But if you start playing with the gains and lowing them, that should help. I know there are some great videos on YouTube that cover the different gains and how to adjust them.
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#3
Well I maidened my vtail and doing fine...some slow circuits and such when I tried a quick forward and back pitch movement and the copter wouldn't stop oscillating front to back. I didn't have time to switch out of self level mode but did cut the throttle to try to minimize the impact. Broke one front boom and motor mount and one rear motor mount. All props and motors are ok. But what would have caused the copter to pitch back and forth uncontrollably like that? Any help is appreciated. Robert
Sounds like the board was getting attacked by vibe -- something I'm wringing out of my V-tail, too, with some success.

Once the v-tail picks up some speed, both the motor load and turbulence from the craft's prop wash increases, with them, the vibe goes up. The vibe confuses a sensor to think a motor is rising when it's actually falling, so it throttles it down, which causes the sensor see a real sudden dramatic drop on that corner, so back up it goes, likely in time to be confused again -- as long as the vibe keeps knocking it off, the error will only get worse.

I've had a badly nicked set of props do this at low speed, replacing them settled it out all the way to a very high speed (1/2 throttle to hiover -> 3/4 throttle Fast Forward Flight). I've also had one of my shock mounts get loose -- the board started to flex because of it, and the craft couldn't even lift out of ground effect without the throttle oscillating.

three things you can do:

- balance the props
- balance the motors
- isolate the control board from vibe

If you haven't done the third well, the other two will only marginally help -- just make sure there's nothing hard physically touching the board -- if it's hard, it's a channel for vibe to be transferred to the board. .
 

Robrotor

Junior Member
#4
That sounds right. I was trying to follow info from some vids but I'm not sure why I have the P gain setting in self leveling at 100. After watching a different vid he had it at 70. Will fix the broken parts and change the p gain. Thanks, Robert
 

Robrotor

Junior Member
#5
Hey Dan, was hovering at the time and just flicked the elevator stick forward and back. That's when it started to oscillate. I think it was the p gain that did it.
 

Robrotor

Junior Member
#6
Well I patched it up and reset the p gain and preliminary results are that it works ok now. Was only able to test it in the house and will do a full test tomorrow. Robert
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#7
Hey Dan, was hovering at the time and just flicked the elevator stick forward and back. That's when it started to oscillate. I think it was the p gain that did it.
Ha! I imagine it'll help better when I read the post ;) well, Glad RCSF could set you on the right path.

Once you get a chance, take her out to stretch her legs a bit. It's amazing how different the experience is when you've got free space to play with.
 

Robrotor

Junior Member
#8
Success!! Dan nailed it. I had the board hard mounted to the frame and even after balancing the props and motors it was still a problem. Mounted the board on pieces of foam I cut from the KK2 packing and hot glued the foam to the frame and the KK2 to the foam. Four batteries with no glitches. Was even able to raise the gains some. Robert
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#9
Only because it's happened to me too! :black_eyed:

Glad you're flying smooth! Now comes the fun part -- learning to bend it to your will!
 
#10
Well you buy cheap, you get cheap. I bought some props off of ebay and I was doing a punch out when one blade on one prop decided to exit abruptly. Two broken arms and two props. Cutting new arms now. Robert