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tricopter problem.

#1
Hi there everyone, I'm new to flite test so sorry if I havent done anything correctly,
I have a problem with my tricopter, it's not a massive problem that prevents flight but it is a problem that may cause a crash in the future when flying FPV so I would like to try and fix it.
The tricopter is a bat bone that I got for a birthday and its only about two months old. I built it myself and all of the electrics are from hobbyking. The flight controller is a KK2.1.5 i think, (the newest one i believe).

The problem however is that when in stable fight or hovering, if I were to pull away sharply on full throttle, there is a dip in the third motor (the rear motor). What I mean is that if I sharply apply full throttle without the stick back down again it will act as though in an unrecoverable nose up and back. Therefore meaning that i have to bring the throttle down again and raise again gently.
Is there a way to sort this problem?
If anyone knows of a solution could you let me know?

Many thanks guys,
 

ztoon

Gone with the Mistral
#2
The problem however is that when in stable fight or hovering, if I were to pull away sharply on full throttle, there is a dip in the third motor (the rear motor). What I mean is that if I sharply apply full throttle without the stick back down again it will act as though in an unrecoverable nose up and back. Therefore meaning that i have to bring the throttle down again and raise again gently.
Many thanks guys,
Hi,
Not sure I understood your pb.
When applying full thr from hovering your tricopter nose down?
Or wobbles when full thr, going then incontrolable in flight ?
Please describe your setup (motor/prop/esc/servo...)
 

makattack

Winter is coming
Moderator
Mentor
#3
Welcome Pezzer!

Not enough information to make a guess, but perhaps it's a CG issue that is made apparent when you go full throttle and the rear motor can't keep up with the two front motors? Maybe you can move the battery more forward?
 
#4
in David's Flite Test - V-Tail Quad - BUILD video, he spend the second 10 mins of the 18 min video showing how to setup the kk2 board. at about 15:45 he does a test showing adjusting the board for the copter not rising level at full throttle, hope this helps. make sure to check your CG is good before adjusting the board
 
#5
I don't use a KK, so I can't tell you exactly the how to fix it, but I know it can be. Watch Davids FT Batbones video. He tackles that problem.
 
#6
Hi,
Not sure I understood your pb.
basically what happens is that when I push full throttle sharply the nose pitches up until i lower the throttle again to arrest the nose up. The thing is that the nose up wont allow me to put in any nose down control. A bit like wind pushing it so harshly that your control input does next to nothing. it just gets blown.

My set up is the bat bone and all the recommended electronics that flite test put up. Otherwise i can't tell you off the top of my head.
 
Last edited:

Ace2317

Senior Member
#7
Where is your battery mounted on your Bat Bone? I fly a Bat Bone and before I put the camera tray on, I strapped the battery in the very front of the frame on the bottom.
 

JAG

New member
#8
Make a change in the "Mixer Editor" in the Menu. Go to the Channel that the motor you want to adjust is on, and adjust the throttle parameter. Sounds like from the description at full throttle, the rear is dipping and the quad is nosing up. So increase the throttle parameter on the rear motor. Increase this parameter until the craft stays level at full throttle.
 

ztoon

Gone with the Mistral
#9
I don't think your problem is CG related. In that case, your pb would be at any throttle position, not only when giving wide open thr.
Are you confident with your soldering? A bad one could gives some weird results.
Your back boom/motor/esc is my suspect #1
Good luck
 
#10
I could be way off base here but it sounds like what you are describing is the rear motor is stalling when you punch it from say low to mid throttle all the way up to full.

I have been having a similar issue with one of my planes. If I hit the gas to hard then the motor tries to spin up makes a buzz sound and then stops until I chop out the throttle and then bring it up very gently. Haven't been able to figure that one out yet...

Probably either a bad motor or back ESC
 

RichB

Senior Member
#11
Your CG is probably too far back.

The rear motor is carrying more weight than the front two motors. This causes no visible problems during normal operation because multirotors are gyro-stabilized, so the rear motor is automatically throttled up higher than the other two when maintaining hover.

As you call for more throttle, the rear motor will max out first, causing the front of the craft to pitch upward. The flight controller will notice this and reduce power to the front motors to prevent a flip-over, but might settle on a stable nose-up attitude. You'll probably notice zero ability to nose-down, as that would require increasing rear throttle (beyond 100%).

If your tail rotor is usually at a significant angle to stabilize yaw, perhaps as a consequence of not using counter-rotating props, then that angle will sap some power from the downward component of the tail thrust. This could exacerbate the problem. If that is the case, you can try shimming the front two motors slightly so that they help out with the yaw correction.


I don't think your problem is CG related. In that case, your pb would be at any throttle position, not only when giving wide open thr.
Good luck
Unbalanced CG wouldn't be apparent at lower throttle levels, since multirotors are actively stabilized.
 
#13
solution solved?

thanks very much, How could I push the CG forward if my battery is as far forward as it can go, and I have a camera coming off the front on a small camera tray of my own design?
But CG and throttle parameters seem like the most logical problem and i will check this

I will also check out David's BUILD video because a couple of people have referred me to that.
Many thanks guys
pezzer
 
#15
Oh sorry, Yes I do,
Forward left and rear are spinning clockwise and Forward right is spinning anti-clockwise.
I still have the rear motor angled at a certain pitch at a given % of throttle. for example i have more automatic tilt when at full throttle than at 50% say. the board controls that though.

pezzer
 

RichB

Senior Member
#16
Can you find the CG on the craft*, then measure distances from that point to each of the motors?

* - the CG will be wherever you can get the craft to balance on your fingertip (with battery installed).
 

makattack

Winter is coming
Moderator
Mentor
#18
Yes, measure CG with everything you would fly with. In a previous post you said you can't really move the battery more forward. If, after measuring the CG, and people here determine it's too far back, one option is to add dead weight -- lead or other heavy objects you can stick to the front area. It's not ideal, but will work in a pinch. Best is if you can move the battery forward. Might need to extend that camera tray you have.
 

JAG

New member
#20
Post a picture of the build so we can see what you have. What lengths are the booms? If the distance from motor center to the center of the KK2 is different for the rear motor, you will have to adjust the throttle parameter to compensate.