High pitched whine from brushless gimbal

[Silverburn]

Hi all,

Bit of a strange one this - eventually got my gimbal to stabilize without vibrating or spazzing out (mostly). Except it seems to be making a high pitched whine in operation - it's constant, whether its at rest or if I shake it about.

It's an alexmos powering 2 x tmotor 2208's from 3S. Gimbal is a cheap $50 from china.

Any idea how I can tune out that whine?

settings are:
pitch: P20 I0.5 D20 Power 30
Roll: P 25 I0.5 D20 Power 60

i might bump powers up a bit; vigorous maneuvers can spaz it out. Too much power = vibes though...

camera is GoPro 2.

 

[RTRyder]

Load the version 2 firmware for the Alexmos board, or if you already have it loaded, go to the advanced tab in the GUI and set the PWM frequency to HIGH, that will eliminate the noise.

It is not possible to tune it out using the PID parameters, it's caused by the 8kHz update rate to the motors, setting it to high bumps the update to 16kHz which is virtually silent.

Ken

 

[DennyR]

The noise is there at 16 khz. but most human ears cant hear it. My ears can barely hear the 8khz. After years of running high speed race engines in a dyno room I am tone deaf to some frequencies. My other half can hear the 16 khz at some distance and finds it very annoying. I think it also depends on your motor winds.

 

[Silverburn]

Guys, brilliant advice - it worked a treat!

However, the first flight has thrown up another problem...I'm getting "flutter" from the vibration mount "balls"! I'll upload a youtube in a minute to demonstrate. But you can see the entire gimbal flutter on it's mounts in any wind. Can you get more rigid balls, or should I just mount the gimbal direct to the legs or frame?

It also spazzes out in turbulent conditions - I suspect there's not much I can do about that, other than flight smooth.

 

[RTRyder]

Unless the gimbal and motors are complete crap the Alexmos board should hold rock steady in the wind like this...

This is an RCTimer $99 gimbal with an Alexmos board hard mounted to a Droidworx AD6. I don't recall which flight control system I had on the AD6 when this was recorded, I recently tested it with a Hoverfly Pro, APM 2.5, and finally reverted back to a Mikrokopter 2.2 upgraded system. I know it wasn't the MK at the time because the gimbal was steadier than the AD6!

These are the settings I'm using on both RCT gimbals I have, powering them at 12 volts through a regulated power supply to the controller. I'd try similar settings to see what it does for yours...

Pitch: P-16 I-10 D-14 Power 60
Roll: P-20 I-14 D-16 Power 120

The rubber balls they include with 99% of the Chinese mounts are useless, they're far too soft to be of any use other than hovering in completely windless conditions. One trick people have used that has worked fairly well is to put a tie wrap through each of the balls and compress them down to the point they still provide some vibration isolation but tight enough that they can't wobble around on the horizontal plane. Put the tie wraps in and don't cut the ends off right away, compress the balls about half way and try it out, if it's still too wobbly squeeze them down a bit more and keep going untill you get aceeptable results. The other option is to do away with them completely and use some solid rubber standoffs like these... http://www.quadrocopter.com/Vibration-Damper-for-Camera-Mount-M3x8_p_42.html I'm using these on my MK Hexa/RCT gimbal and they work much better than the rubber ball setup.

Ken

 

[DennyR]

I think in many cases the rubber balls make the vibration worse. unless the gimbal is suspended so that the center of mass is supported equally then it creates an oscillation. helis can throw out some big vibrations that need to be treated carefully, batteries and gimbal accessories all need to be suspended exactly though the center of mass or they start to move more than if mounted solid.
A two axis gimbal can be very difficult because there is no balanced movement in pan. So you can see bad movement in pan induced just through bad mounting alone.

 

[Cameraj]

What lense are you using? I get a few jerks or bumps in wind and forward flight, any deas on settings?
Thanks