Servo feedback issues. Need help!

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Servo feedback issues. Need help!

Postby KobraX22 » Sat Mar 10, 2012 6:10 am

Hi Bruce (and other forum goers),

A few months ago I decided to dive into the world of RC.
Over the past few weeks I've been building my first RC plane. And I'm glad to say that I'm almost at the point where I can take it out for it's maiden flight. :)
I currently have it set up so the BEC from the ESC (Mystery Blue Series 30A) is powering the receiver and the all four servos (2 for the V-tail, 2 for the ailerons).
But I've run into a problem where the servos (HXT900's) seem to be producing feedback and causing the motor to spike/stutter.

Example: Throttle stick is at 0%, move any of the servos aggressively, motor powers up to a few hundred RPM for a fraction of a second.

I've tried winding the the control cable from the ESC through a ferrite coil, but this had no impact.
Any help will be greatly appreciated.
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Re: Servo feedback issues. Need help!

Postby BillGriffiths100 » Sat Mar 10, 2012 1:44 pm

The most likely explanation for your problem is that the BEC in the ESC is not up to supplying 4 Servos.
It's causing some kind of brown out to the receiver, which is then sending erroneous signals to the ESC.
Unplug some of the servos and see if the problem persists.
If the problem goes away with less servos, then the BEC is the cause.
Get a switching BEC rated at 4 amps or more and use that instead of the ESCs internal BEC.
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Re: Servo feedback issues. Need help!

Postby KobraX22 » Sat Mar 10, 2012 9:36 pm

It happens even with just 1 servo. The BEC in the ESC is rated at 5.0V / 3A, there is no way that a single 9g servo with no stress on it could draw more than 3A.
I do have separate SBEC, but wont this mean that I'll need to add an extra battery? Or could I just run the ESC and SBEC in parallel with the main battery?
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Re: Servo feedback issues. Need help!

Postby RCModelReviews » Sat Mar 10, 2012 9:47 pm

What RC system are you using?
RCModelReviews.com, just the facts.
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Re: Servo feedback issues. Need help!

Postby KobraX22 » Sat Mar 10, 2012 10:07 pm

I bought a Turnigy 9X set. I have made several modifications to the transmitter (ER9X firmware, custom battery, backlight with firmware control, and I moved the aerial to the module so I can replace it later).
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Re: Servo feedback issues. Need help!

Postby ergocentric » Sun Mar 11, 2012 6:18 am

unplug the esc/bec and plug in a battery, retry

check your transmitter battery
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Re: Servo feedback issues. Need help!

Postby BillGriffiths100 » Sun Mar 11, 2012 9:36 am

Yes with a battery instead of the ESC plug a servo into channel 3 the motor control.
If the servo twitches instead of staying still when you move the other sticks the ESC is not to blame.
If the servo twitches then the RX may be faulty or there may be a problem in the TX software.
If the problem is in the TX software a re program might cure it.
You might have some inadvertent mixing going on due to a programming fault, this has happened before, the processor not quite taking the program, leading to strange faults like the screen blanking out for example.
Compromising with out of control government is like living with a lion, sooner or later the bloody thing will eat you .

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Re: Servo feedback issues. Need help!

Postby KobraX22 » Mon Mar 12, 2012 3:37 am

I'll try this when I get home.
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Re: Servo feedback issues. Need help!

Postby KobraX22 » Tue Mar 13, 2012 9:04 am

Okay, So I disconnect the red pin from the ESC to stop the BEC.
And I connected a dedicated SBEC.
This seems to have solved the issue completely! :D
I'm quite sure if this is the correct usage of the term, but I think I must've been having constant brownouts.
I noticed that when using the ESC's BEC, the light on the receiver would fade/flicker whenever I moved any of the servos.
Now that I'm using a dedicated SBEC, the receiver light stays constant, and servo movement is much smoother.
I guess the on-board BEC in the Mystery Blue Series 30A ESC is just a piece of crap.

Thank you to everyone for the help and suggestions!
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