Tricopter Unstability Problem!

[ANDMan55]

So i have built a Tricopter. I like it, but my problem is that sometimes when i am flying, it does not fly stable and starts teetering slowly and violently. I have played with the P and I gains and limits but i dont see any change as I add or subtract numbers 10 at a time. It flys well when im hovering about 3 feet off the ground and going around with just aileron and elevator, but when i get high up it starts to wobble...Especially on decent(even slow) it has a very slow oscillation and tries to over correct way too much at like 45+ degrees. Very frightening.

The props don't cause too much vibration, except for one of the motor's does create some and balancing does not seem to aid that(shaft seems slightly bent from factory...)

~My parts list is~

x900 frame
3X Afro 30A ESC
3X NTM PropDrive 28-30s (short shaft) 800kv 300watt
KK2.1
12X4.5 SF props
Hitech HS-65MG
OrangeRx R620
OrangeRx R100

And currently using my RC car battery.. Dymamite Speedpack 5000mah 3s 20c Lipo
And sometimes my two Airsoft lipos in parallel.. 2X Turnigy Nano-tech 1200mah 3s 25-50c

I did have the KK2.1 mounted via included nylon mounts, but i am going to test using the foam case it came in and hot gluing that on. Last time i flew it i had my camera mounted on it and it just lost all control and was flipping in stability mode almost upside down and fell about 100ft into some tall grass...luckily only one prop broke

If you need any pictures or something, ask and ill be more than happy to do so. And thank you in advance!

 

[Craftydan]

Hey Andman!

Welcome to the forum!

The wobble on descent is due to the props moving through their own propwash -- it's a real issue that can even crash full scale helicopters and making things smaller only makes this effect worse. Best way to overcome it is to keep some lateral movement as you descend -- any direction . . . some folks even gently spiral downward as they descend, but keep in mind if you want to go side-to-side, you still have to stop to go back the other way.

You might also be experiencing higher winds the further up you go. Gains set to the bleeding edge can become unstable as you start picking up more vibration from winds or higher throttle, Unless you plan on flying high and fast more often, a little bit of wobble every now and then isn't bad, so long as you can expect it.

 

[ANDMan55]

Okay, that's what I have been reading around. Didn't think it would cause it to be this bad haha. Thank you for the quick reply, now I just have to fix my tilt mechanism and get flying again..