Gimbal 'judder'

M

Mike Toy

Member
Good morning All,

And greetings from sunny Barbados. I fly a DJI-S800 with an Alware Lensman 3-axis gimbal. Roll and tilt are brushless, the pan is a regular servo. Gimbal controller is an Alexmos, software is BCG 2.2, camera is a Nikon D5300.

Although the gimbal performs fine on the ground as soon as the vehicle is airborne the gimbal starts to judder from side to side. Below is a link to a short video clip; if anyone has any suggestions as to what might be causing this and how it can be rectified I'd be most grateful.

Gimbal judder

Thanks,

MIKE TOY
 

H

HEXATOM

Member
Hi Mike,

Have you tried connecting to the GUI via USB and increasing the power & PID settings? It can be a lot of trial and error hitting the 'sweet spot'
 


H

HEXATOM

Member
JoeBob said:
FWIW: The DiscoPro family says NEVER to upgrade beyond Simple BGC 2.1.
Click to expand...

Hi Joe, thanks for that, is their any specific reason? I have noticed that a gimbal I use with BGC v2.3 isn't as reliable as one a second gimbal I have on 2.1, as in it does seem a little more 'twitchy' in windy conditions
 

M

Mike Toy

Member
Yes,

In fact I'm now decreasing them as if they're too high then the gimbal starts to vibrate on it's own. It may be something to do with the dampers - I'm using those supplied with the gimbal plus the dampening kit (blue balls) that DJI brought out for the S-800. The more dampers the more movement there is between the gimbal and craft. Not sure if this is a good or bad thing, I remember reading that some people had bough the damping kit and then removed it as it actually made things worse. As you say, I think it'll be a (long) process of trial and error.
 

H

HEXATOM

Member
Mike Toy said:
Yes,

In fact I'm now decreasing them as if they're too high then the gimbal starts to vibrate on it's own. It may be something to do with the dampers - I'm using those supplied with the gimbal plus the dampening kit (blue balls) that DJI brought out for the S-800. The more dampers the more movement there is between the gimbal and craft. Not sure if this is a good or bad thing, I remember reading that some people had bough the damping kit and then removed it as it actually made things worse. As you say, I think it'll be a (long) process of trial and error.
Click to expand...

I used the cable / zip tie trick to compress them a little. Made quite a difference. Moon gel on the camera tray also eliminated 'jello' in combination with a ND4 Filter.
 

H

HEXATOM

Member
What are your PID settings. The video looks like it's either the dampening balls swaying or the motor hasn't got enough 'I' setting. I'd go for the dampening and try zip ties to compress the dampening rubbers a little and stop that sway
 

M

Mike Toy

Member
PID settings were preset by the gimbal manufacturer and are as follows:

P I D

ROLL: 8 0.05 32

PITCH: 7 0.05 28

Thanks…….
 



H

HEXATOM

Member
I'd secure the dampeners to start, don't take them off, just use zip ties as they will absorb some vibration from the frame, secure them enough so they are slightly stiffer but not to overtight.

Depending on you Power setting, to me the D settings are slightly high and not enough I setting. Decrease your D level in steps of 2 untill you get smooth traces in the real time monitor tab. Then increase the I settings until you see the Roll / Tilt dial responding quickly to any side to side or front to back movements. This also tends to strengthen the hold.

Trouble is with this is there seems to be no defined sweet spot for different set ups.

I started by setting my PIDs all to zero, after setting the main power in the right hand of the screen where you set the number of polls. Then started tweeking the PIDs while monitoring the Trace tab to find maximum where is starts to vibrate then backing off in small steps. I have upgraded to GUI v2.3 where the auto setting gets you around the right ball park figures with Power Num Poles & PID settings, you can tweak from a better starting place after the Auto set up

Hope this helps
 


dazzab

dazzab

Member
That looks like it's coming from the pan axis. You mentioned that axis has a normal servo on it. I didn't know that AlexMos could drive a servo. Isn't it just for brushless motors? It would be easy enough to test. You could disconnect that server and lock the third axis in place. Go for a flight and see if the movement is still present.
 

M

Mike Toy

Member
You're right, the Alexmos only controls the roll and tilt axis, it's not connected to the pan. There is a little play in the pan axis but I can't see why it would move from side to side by itself.
 

M

Mike Toy

Member
FYI I disconnected the gimbal controller and flew it yesterday - exactly the same issue. As soon as you feed in power left/right or backwards/forwards there is a momentary judder. So, looks like something is 'loose' Only thing I can think is the pan axis (as you quite rightly pointed out) but how to get around that? There is the normal amount of movement between the gears but it's not a lot. Change to a brushless motor for the pan? Sounds like a lot more fiddling about…….Any ideas would be welcome….
 

You must log in or register to reply here.
Top