Why the jitters???

[Richlizard]

In my desperate attempt to find out why my F550 had a recent ';apparent'; flyaway, I am looking at every little detail that could possibly have causes it.

This probably has no bearing whatsoever, but what I have noticed in comparison to my mate';s almost identical machine is that my arms shake pretty bad at almost point of lift-off. His don';t. The props are all very well balanced.

Hopefully you can see what I mean in this video. I have seen this before, but having searched google for a couple of hourse, I can';t find where I saw it before which probably gave the solution.

So can anyone throw some light on what causes this...

Cheers

IMG 37171

Bugger, I just watched the video and you can hardly see it. But I promise  the right and left arms wobble like crazy. They barely shake at all on my mate';s.

[flybywire]

I';ve seen that shaking too, it was a forum member hereabouts, it shook like crazy before lift off, but quitened down once in the air, may have been Donald, but can';t be certain.

Andy.

[Col_M]

Things shaking like crazy at certain points but being fine at other speeds is usually resonance. I';ll bet that your friend';s nearly identical quad has different motors or props, or on the other hand one or more of your motors is slightly imbalanced and causes problems at the systems natural frequency that your friend';s doesn';t exhibit.

[Richlizard]

Things shaking like crazy at certain points but being fine at other speeds is usually resonance. I';ll bet that your friend';s nearly identical quad has different motors or props, or one the other hand on or more of your motors is slightly imbalanced and causes problems at the systems natural frequency that your friend';s doesn';t exhibit.

Identical props and motors... purchased at the same time.

How do you balance a motor? I will do anything to try avoid that sick flyaway feeling.

[Col_M]

The easiest way to balance motors is dynamically.

You can do the laser method with a mirror attached to the leg, just holding the leg and feeling the vibrations, or listening.

With all of them you add a bit of tape to one side or other of the motor and see if it improves or worsens the vibrations, it';s all trial and error really. You can also put a zip tie on the motor and move the lump around to shift the weight around.

There are lots of videos and guides about, it';s been mentioned a few times on this forum so a search should be fruitful! 

[tony]

ERM i no you have had this flying but 1 simply reason could be as simple as 1 of your motors are  spinning the wrong way  are more likely 1 of your props are on the wrong way around

don';t ask me how i no please   

[Richlizard]

ERM i no you have had this flying but 1 simply reason could be as simple as 1 of your motors are  spinning the wrong way  are more likely 1 of your props are on the wrong way around

don';t ask me how i no please   

I won';t ask how you know. Cough.

But I do know that the craft would not fly with a prop or motor is spinning the wrong way.

Thanks anyway :)

[tony]

any rc flying machine will fly with a prop on the wrong way around  motor you may be right but with a hex 7 motors v 1 it mite just mite fly

[virginprops]

mine did this untill i balanced my props. It was fine when in the air but due to accelerating hard to take off i would get bad jitters.

[Richlizard]

any rc flying machine will fly with a prop on the wrong way around  motor you may be right but with a hex 7 motors v 1 it mite just mite fly

7? A heptacopter? There';s a thought 

[n506]

You get a huge amount of turbulence when you';re on the ground or within 50cm or so of the ground. That';s why folk find it so hard to fly a multicopter when they';re timid and don';t want to take it too high. They bounce about trying to hold onto it thinking that folk who fly these have insane skills. Once it clears a little more height, you get a nice smooth airflow.

But why they';re not all doing that is the question. Could be some of the cabling/leds is catching the airflow a bit more on that arm, could be the arm is a slightly different density to the other arms causing a different resonance frequency, could be a bad bearing in one of the motors, slight chip on one of the props (despite being balanced, the airflow might not be as clean as it could be - I have one like that on my quad that I fling about due to hitting branches too often).

Me personal recommendation, if you';re desperate to figure this one out, would be to swap that motor and prop with another motor and prop that is rotating in the same direction. If the jittering starts up on the other arm, you';ve got a motor/prop issue. If it stays on the same arm, you';ve got a resonance issue with the arm. If nothing else, it narrows down the issue for you in a relatively scientific way.

[Richlizard]

Thanks n506.

I did actually swap the motors on those arms... nothing changed.

Perhaps I will change props with my friends and see if that makes a difference.

[n506]

Well sounds like it';s resonance on that particular arm for some reason. If you have a spare arm, you could perhaps swap it in and see if it changes things?

[Richlizard]

The reason I recently took it apart was to add two new arms... to the front though, not side... so that they are all black.

I don';t actually remember the wobbles being there before, so I suppose every chance it is something I did but having checked everything a dozen times I can see nothing.

Is there a chance putting new arms on the front has upset the balance of those on the side? Na, I am talking bollox clutching at straws I think.

[n506]

In all honestly, it was probably there... it';s amazing the things you spot as soon as you start looking closely after having a problem!