My mini H-quad was flying well, so I decided to try the Multiwii Se 2.5 I had lying around. I got it setup using the Multiwii config, and was surprised how stable it was.
I was on stock settings and decided to be clever and play around with the settings. After a test flight I found the stability was gone so decided to start over and hit the rest button. After calibrating everything, the quad now has throttle problems. When I increase throttle it suddenly jumps up and down like a yo-yo. Roll,Pitch and Yaw are ok but I have no control over throttle.
I have tried re-calibrating, but no luck. Finally put the KK back on and it hovers fine. What am I missing?

Sir their are various reasons for it
1) p value of altitude is way too high
2)barometer is not covered with open cell foam
3)altitude hold is turned on
4)multiwii software is configured incorrectly
5)caliberating escs using esc_calib_cannot _fly

I hope this helps sir

Happy flying

Regards
Chintal
Rcmumbai.com

Thank you for the reply but, P values are stock as before. The barometer was not covered before and it flew great. Altitude hold is off. Does resetting the Config throw the esc calibration off?

Please post the P , I ,D values or take a screen shot of the configuration and post.

Esc calibration wont change if you reset your settings on multiwii. Stock values shouldnt have worked out of the box with a mini quad, because stock values are usually for a bigger quad but who knows, these things keep surprising me.

Anyways its either high p value for "Level" or due to high vibrations. P values of roll/pitch only needs to be decreased if your quad oscillates on roll/pitch axis while bouncing up and down, in the end adjust I&D accordingly.

Similarly changing battery also results in a bouncy quad, eg: going from 2s to 3s, if you have tuned your quad for 2s. I had the same issue, KK's dont mind this.

For vibrations, its best to avoid it at the source, like unbalanced frame/motors/props. Use of foam or any vibration absorbing material to mount board is a good idea. If you think there is nothing much that can be done, then FYI you can change LPF setting in Config.h file. Uncomment in the decreasing order one by one and see which one works. Ideally its recommended not to go below 42khz. Again KK's are really forgiving when it comes to vibrations too than multiwii.

/* MPU6050 Low pass filter setting. In case you cannot eliminate all vibrations to the Gyro, you can try
         to decrease the LPF frequency, only one step per try. As soon as twitching gone, stick with that setting.
         It will not help on feedback wobbles, so change only when copter is randomly twiching and all dampening and
         balancing options ran out. Uncomment only one option!
         IMPORTANT! Change low pass filter setting changes PID behaviour, so retune your PID's after changing LPF.*/
      //#define MPU6050_LPF_256HZ     // This is the default setting, no need to uncomment, just for reference
      //#define MPU6050_LPF_188HZ
      //#define MPU6050_LPF_98HZ
      //#define MPU6050_LPF_42HZ
      //#define MPU6050_LPF_20HZ
      //#define MPU6050_LPF_10HZ
      //#define MPU6050_LPF_5HZ       // Use this only in extreme cases, rather change motors and/or props

Well its better you recalibrate the esc
A picture of pid and a video of your quad flying will help find the problem

@sidewinder thanks for the info. I have to admit there was a bit of twiching with the stock settings but it hovered great. Will try to eliminate vibs and will post GUI screen shot.

I have anti vibe mount for flight control board to solve your problem

My Multiwii conf.

sir yaw is high in p please reduce it and try

i hope it helps

Regards
Chintal
Rcmumbai.com

sir change the Yaw P rate to 6.

regards
Ujvictor

Yaw values look normal. I'm using the same stock values for yaw on my mini quad(250/280), so that doesn't seem to be the culprit.

Its probably vibration(board may have got displaced or loosened, try to mount it on foam pad or something rather than screwing it to the quad. CF is very vibration friendly), or
You probably switched batteries from 2S to 3S, because if it had worked alright on stock values in the first attempt, it should have worked during the second attempt too IMO.

Also try to disable the headfree mode all together. Just use acro or angle or horizon mode for time being.
Attaching my PID's, N I'm using 42hz LPF setting.

PS: You can also upgrade to Multiwii 2.3

I tried the 42hz LPF settings ,but when I upload sketch I get the "avrdude stk500_getsync() not in sync resp=0x00" error. It says upload complete but the error message is also there. For board type I set Arduino Promini w/ATmega328.
Any suggestions?

Try Duemilinove with ATmega 328p board .
I use a nanowii 328p, so selecting option was easier

Managed to get the quad to an acceptable degree of stability. I decreased the PID for Pitch and Roll. I also put a little distance between the RX and the MWC. I have no Idea what fixed the issue of altitude but it flies well enough. About the sketch problem, I noticed that when I first open the software, it shows "sketch_june12a" on the tab. What does this mean? Did the sketch get uploaded despite the error message? 

Great to hear it sir
Whats the pid now ?

Happy flying

Regards
Chintal
Rcmumbai.com

@ Sidewinder and Chintal: Thanks for the info this was helpful in setting up my multiwii as well

Most welcome sir
Happy flying

Regards
Chintal
Rcmumbai.com

When you open Arduino IDE, it opens a new file and names it by default as "sketch_june12a", probably using current month/date. But that shouldnt matter because you would have to open the multiwii sketch which should open in a new window.

The error you are encountering is a communication error between the board and pc, which means the software couldnt successfully communicate with your board. So dont think sketch was successfully loaded. You can check this by uploading a different sketch (multiwii 2.3 sketch), and we can verify whether upload was successful in the multiwiiconfig on the extreme top left of the window where it mentions the current version.

Reasons for error can be many such as missing/incompatible drivers, usb cable fault, selection of wrong board under Tools> ->Board or wrong port under Tools> ->Serial Port, software compatibility issues,  incorrectly plugging ftdi programmer etc. You would have to eliminate them one by one to find the exact cause. You can find some solutions which helped a couple of users @

https://www.google.co.in/search?q=avrdude+stk500_getsync%28%29+not+in+sync+resp%3D0x00