Gimba pitch jitter problems...

[AndyR]

Hi folks. I've got an issue with my gimbal that I'm having a hard time figuring out. I've got a TBS Discovery which I've modified to hold a gimbal. (http://www.goodluckbuy.com/dji-phan...for-gopro3-fpv-aerial-photography-blalck.html) <<<This one here. On the ground, everything is fine. The gimbal is smooth and I don't have any problems. I can really give it a workout, no problems.

I can have the TBS hovering right in front of me swerving back and forth and the gimbal performs flawlessly. Nice and smooth. Once I get some altitude, or gain some real momentum.... that's where things start twitching. The roll seems fine, but the pitch starts twitching wildly.

So I can be hovering or moving slow at low altitudes, and everything is fine. If I gain speed, it twitches. If I go above 40' and hover, it will twitch. (I can only imagine it's the wind causing this, right?)

I do have pitch control hooked up to the Naza, and I have tried flying without it connected. Same twitchy results. I have tried a multitude of different PID settings on the Alexmos board with this same problem always arising.

I can share more details about my setup tonight, but I'm just curious if anyone has any ideas based on my symptoms. TIA!

Edit: Oh btw... these might be a little more than a "jitter". The pitch axis jumps up and down by probably 10-20 degrees... at times going into a full blown fit of disorientation.

 

[tstrike]

Don't hook up the pitch through the naza, go direct to an aux channel on your receiver. Also, you should only need your signal wire and a ground wire going into the receiver, so disconnect the red wire from your servo lead. Don't know if this is the cause of your problems but just a heads up.

 

[SoCal Blur]

Can you post a video with an example of what it is doing?

 

[jes1111]

Sounds like it could be a wind pressure/balance problem. How well balanced do you have the camera? If the balance is even slightly off and you add wind pressure and the motor is only just strong enough to hold the camera still in a no-wind situation then... see what I mean? Can you "excite" the same/similar behaviour on the bench by pushing against the camera?

 

[AndyR]

Don't hook up the pitch through the naza, go direct to an aux channel on your receiver. Also, you should only need your signal wire and a ground wire going into the receiver, so disconnect the red wire from your servo lead. Don't know if this is the cause of your problems but just a heads up.

I'm aware it does complicate things... but I have tried the gimbal without Naza or anything but power, and it still has this same twitch.

Can you post a video with an example of what it is doing?

Certainly. Uploading a video now. Will link it once my super slow DSL manages up upload the file.

Sounds like it could be a wind pressure/balance problem. How well balanced do you have the camera? If the balance is even slightly off and you add wind pressure and the motor is only just strong enough to hold the camera still in a no-wind situation then... see what I mean? Can you "excite" the same/similar behaviour on the bench by pushing against the camera?

It certainly seems like it's related to wind. I'm new to gimbals, but I'd say I'm balanced. I'm using a GoPro2, and when the gimbal is unpowered the unit stays balanced pointing straight ahead.
When powered, I can blow on the camera with no ill effects. I can tap on the gimbal and it seems to give sufficient resistance to handle a little wind over such a small surface area. I'm unable to replicate this problem while not flying.

Props are balanced, but motors are junk. (NTM) Vibration could be an issue, since I actually don't have any vibration dampening between the frame and gimbal. But then, why would this only become a problem in the wind? Low altitude slow flying seems fine.

I've attached my gimbal settings below.

View attachment 17885View attachment 17886

 

[jes1111]

Vibration could be an issue, since I actually don't have any vibration dampening between the frame and gimbal. But then, why would this only become a problem in the wind? Low altitude slow flying seems fine.

Then it could be a vibration/resonance issue - maybe the wind element is "the last straw". Try re-doing the mounting with some damping material in between the frame and the gimbal - some foam or some rubber - it's not likely to solve the problem, just need to see if it changes the behaviour in any way - if it does, then you know you're heading in the right direction.

 

[AndyR]

I'll see if there's something I can do to add some dampening... but adding dampening to my setup might be difficult.

https://vimeo.com/93328787 Gimbal flight test

https://vimeo.com/93327974 Gimbal mirror test

 

[Vortex]

Looking at your first video I'd say look at re-mounting the IMU to try and isolate it against vibrations better and check the prop balance

 

[AndyR]

Looking at your first video I'd say look at re-mounting the IMU to try and isolate it against vibrations better and check the prop balance

Padding the IMU might be an easier task to start with. I'll try that tonight. Sigh... too few hours in the day...

 

[Stacky]

It certainly seems like it's related to wind. I'm new to gimbals, but I'd say I'm balanced. I'm using a GoPro2, and when the gimbal is unpowered the unit stays balanced pointing straight ahead.

The balance is critical and there are 3 axis to balance. If you move the gimbal to any position the camera and gimbal should stay in that position. It must not return to level. The 1st axis is roll, then pitch and finally the cog of the camera in the gimbal. Its the cog balancing that catches people out. If the cog balance is out then wind will become a problem.

I cant find a video showing how but this video shows what should be happening

 

[AndyR]

Ah!! Thanks Stacky. You are correct, I hadn't quite understood that aspect of "balancing". That's very helpful. Will check into that tonight.

I also just pulled the trigger on a GoPro Black + moments ago...

 

[AndyR]

Well I've got a thin strip of foam under my gopro.. which lifted it just the right amount to be truly balanced. (and supply some vibration buffering to the camera)

I've also remounted my IMU with some foam. At first it was allowing for too much movement which made the gimbal go crazy. I compressed it a bit with a zip-tie and I think that's a good compromise.

And now we wait for the rain to stop. Nothing but rain on the forecast for almost a week! Thank you all for your input and help. Hope I can return it some day.

 

[Vortex]

Well I've got a thin strip of foam under my gopro.. which lifted it just the right amount to be truly balanced. (and supply some vibration buffering to the camera)

I've also remounted my IMU with some foam. At first it was allowing for too much movement which made the gimbal go crazy. I compressed it a bit with a zip-tie and I think that's a good compromise.

And now we wait for the rain to stop. Nothing but rain on the forecast for almost a week! Thank you all for your input and help. Hope I can return it some day.

I think you're on the right track...Good Luck

 

[AndyR]

Well that really got most of the larger twitches out of the gimbal. I still get them when I have a lot of speed, but it's manageable. Now I just need to work on the smaller vibrations in the picture.

As it turns out, I also had the IMU sensor set incorrectly. When I pitched the camera down, the sensor would think it was pointing up. I also resolved that.

I'm also going to try out a 4s battery. I currently run 900kv motors, 10" groupners, and 3 cell batteries... and I'm not getting enough lift to make flying comfortable.

 

[AndyR]

Just to follow up on this... in case anyone else is using this for troubleshooting on their own gimbal: The real problem with my setup was not vibration to the IMU, or even balancing for that matter. (though both are important aspects of course) It was most likely the fact that my axis setup was wrong in the gimbal software. My sensor thought I was pointing up when it was pointing downwards. Rookie mistake!