LibrePilot Forum

General Category => General Discussion => Topic started by: mak24 on March 25, 2018, 07:54:01 pm

Title: Screws Loosening mid-air
Post by: mak24 on March 25, 2018, 07:54:01 pm
My Quad is finally flying perfectly in Basic and INS13 modes.  Thanks to all the great help, especially from The OtherCliff, f5soh and so many others.

So I decided to use Autotune today, again.  During AutoTune, the quad took a tumble.  Upon inspection, I found that the screw on Motor 1 was loose.  This is the second time that it has happened, meaning motor screw getting loosened during Autotune. 

I have SunnySky 2212 motors, with 1084.5 APC props.

Any advice would be greatly appreciated, as usual.
Title: Re: Screws Loosening mid-air
Post by: TheOtherCliff on March 25, 2018, 08:47:34 pm
Autotune does the same things that you do wiggling the sticks quickly, so it isn't the problem.  :)

Vibration causes loose screws:
- Balance your props well, and even in both directions (long way and short way).  I like to do a final pass with the prop on the motor while watching telemetry of the accels and gyros, running one motor at a time.  A piece of plastic electrical tape here or there for balance to see what makes it better.  Of course this is dangerous and you have to be careful and be willing to accept the responsibility and risks.  Invest in a good prop balancer and understand how to work around it's limitations.

- If needed, use a tiny amount of blue Locktite on all your motor screws
Title: Re: Screws Loosening mid-air
Post by: mak24 on March 27, 2018, 05:30:51 am
Thanks The OtherCliff!

Agree that Vibration causes loosening of screws.

I use a Du Bro prop balancer to balance the prop shaft and the hub (I am assuming that is what you mean by long and the short way).

I have started balancing the motors by using the method here.  Thoughts?

Are you saying that after balancing the motors and props, i should try to reduce the vibrations further with the prop on and the motor running, one prop at a time?  I guess with proper precautions that should be OK.  If I do run this test, I am assuming that for Accel and Gyro, I should see least displacement of the graph lines in the scopes window for gyro and aceel.  Is that correct?

An observation.  With no power to the quad (just the USB connection to the FC), I see quite a bit of displacement in Gyro. Please see attached.  Is that normal?
Title: Re: Screws Loosening mid-air
Post by: TheOtherCliff on March 27, 2018, 05:49:53 am
Yes to (carefully) try running motors with props on, one at a time, and moving a small (say start with 1cmx1cm for a 10 inch prop) piece of plastic electrical tape to different places on the prop (say one tip then the other then half way, etc.) to see if it helps.  But the video just shows balancing the motor alone and you can't really do it that way with a prop on.  Put a small mark on one blade to help you keep track of which blade is which.

You don't have to do this always, but it helps you know if you are really getting a good balance.  If it doesn't help, don't do it again...

Another thing that causes vibration is tracking where if you look at it from the side while you slowly rotate the prop by hand, you can see that one prop tip is higher than the other.  One or two crescent shaped pieces of paper under the low blade will bring it up to level.

Yes, the scope is normal.  It is "auto ranging" so that it will change the range until it fills the scope.
Title: Re: Screws Loosening mid-air
Post by: mak24 on March 28, 2018, 03:01:45 am
Great lots of homework. Thanks TheOtherCliff😀

About tracking, groeat tip!  So aside from tracking the prop on say a prop balancer, I should also track all the props while they are on the arms of the quad.  This will be for all the props, so prop for motor1 will be tracked against motor2, 3and 4. And then prop 2 against prop 1, 3 and 4.  And so on.  Am I right?

Will report back when done.

Title: Re: Screws Loosening mid-air
Post by: TheOtherCliff on March 28, 2018, 03:45:16 am
No.  The prop for motor #1 will be tracked against the shaft of motor #1.  It doesn't matter that the motor/shaft/prop might point slightly off from perfectly straight up (that is handled automatically by stabilization and does not add vibration).  It should look like one disk when the prop is spinning and it is viewed from the side, not two disks.

Prop on motor shaft like this:

not like this:

Title: Re: Screws Loosening mid-air
Post by: mak24 on April 02, 2018, 02:19:11 am
Well guess what.  After all the troubleshooting, I realized that it was a noisy motor with perhaps old/loose bearings.  This was the motor where the motor nut was coming loose.  Changed the motor and voila!

Thanks for the tracking tips TheOtherCliff!

Need to do more field testing and flying, but things are looking good for another summer  of flying