Hitec 311 potentiometer failure

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Hitec 311 potentiometer failure

Postby pulsext » Sun Apr 21, 2013 1:09 pm

I had my elevator servo fail on me today (thankfully after my four flights!) and after very careful inspection it was clear that the pot has failed. There is mostly no movement with stick inputs and when there is, it is intermittent and only working with the servo held in different angles. My question is what would cause the pot to fail like this? I obviously do not want to just replace the servo only to have it fail in the same manner! Could it be the higher voltage of the 6.6v life pack? Or could it be that there was too much load on the servo? It is worth mentioning that it is a new servo with less than 10 flights on it. Any advice will be gladly appreciated!
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Re: Hitec 311 potentiometer failure

Postby BillGriffiths100 » Sun Apr 21, 2013 5:03 pm

Get the screwdriver out and find out!
Learn by taking things apart it's not working how can it make things worse.
The higher voltage is very unlikely to have caused the problem.
Most likely a loose wire.
Compromising with out of control government is like living with a lion, sooner or later the bloody thing will eat you .

You accept the tyranny of the state when it's not being applied to you, when it is: it's too late.
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Re: Hitec 311 potentiometer failure

Postby pulsext » Sun Apr 21, 2013 5:25 pm

I have taken it apart and unfortunately there is nothing that seems out of place! I have since tested the pot by measuring the resistance and it seems fine, so that blows my initial theory out the window. I think it is probably the motor. It will only run if it is held upside down , if that makes any sense!
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Re: Hitec 311 potentiometer failure

Postby quarry44 » Mon Apr 22, 2013 12:38 am

I imagine Hitec servo's are now made in China,like everything else.Hence quality control would be non-existent.I would very carefully check the soldering on the motor contacts,or wires,as the case may be.
In any case,servo's are now so cheap,it's probably simpler just to bin it,and replace with a known good one.
If you do manage to fix it,use it on a less critical control,like throttle or rudder.If it fails then,you at least have a chance to get your plane down in one piece.
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Re: Hitec 311 potentiometer failure

Postby BillGriffiths100 » Mon Apr 22, 2013 8:25 am

It will only run if it is held upside down , if that makes any sense!

Yes the brushes and or the brush holder is loose.
Possibly but unlikely the brushes are burned away.

Open up and look you have nothing to loose!
Also if your shopping for replacements essentially the HK 15138 is a similar quality servo and has a good reputation.

http://www.hobbyking.com/hobbyking/stor ... 0_17s.html

Get a bag full of these for the price of a few 311's!
Last edited by BillGriffiths100 on Mon Apr 22, 2013 1:15 pm, edited 2 times in total.
Compromising with out of control government is like living with a lion, sooner or later the bloody thing will eat you .

You accept the tyranny of the state when it's not being applied to you, when it is: it's too late.
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Re: Hitec 311 potentiometer failure

Postby A.T. » Mon Apr 22, 2013 9:32 am

pulsext wrote: I had my elevator servo fail on me today (thankfully after my four flights!) and after very careful inspection it was clear that the pot has failed. There is mostly no movement with stick inputs and when there is, it is intermittent and only working with the servo held in different angles. My question is what would cause the pot to fail like this? I obviously do not want to just replace the servo only to have it fail in the same manner! Could it be the higher voltage of the 6.6v life pack? Or could it be that there was too much load on the servo? It is worth mentioning that it is a new servo with less than 10 flights on it. Any advice will be gladly appreciated!


For all analogue servos, including HS-311, suggest best compromise is to run a switchmode regulator at 5v
The higher the voltage, the higher the servo speed and torque and heat generated which also results in a much faster burn out
of components being reason many new digitals have a partial or all alloy case.
Without viewing the servo and installation, it is difficult for readers to get a full understanding of where any problem originated.
The following may assist:
. BURN IN - Aging of RC Transmitter, Receiver & Servo components
. Servo - Operating Voltage Range - (Hitec) usage with NiMH, Lipol & A123 batteries.
. Servo - How to Diagnose Servo Failures & Repair Servo
. 101 - Servo Repair - Finless Bob's Video
. 101 - Servo FAQ & picking the right servo for the job

Much more information available under sub sections
"Glitches & Jitter in Receiver, Servo & ESC - Causes and Cures"
"Servo - Alterations, Calculators, Databases, Leads, Repairs, Convert to an ESC or winch & FAQ."
below
"Radio Systems, Accessories, Alterations and FAQ" at
Alan's Hobby, Model & RC FAQ Web Links

Alan T.
=======
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Re: Hitec 311 potentiometer failure

Postby pulsext » Mon Apr 22, 2013 3:35 pm

BillGriffiths100 wrote:Yes the brushes and or the brush holder is loose.
Possibly but unlikely the brushes are burned away.


That makes perfect sense

A.T. wrote:For all analogue servos, including HS-311, suggest best compromise is to run a switchmode regulator at 5v
The higher the voltage, the higher the servo speed and torque and heat generated which also results in a much faster burn out
of components


It is possible that I was pushing the servo to it's limits in terms of its amount of travel (I battled to get the amount of throw that the ARF manual suggested). So maybe that coupled with the higher current led to the motor burning out?
Do you have any suggestions for "reliable" regulators? The plane has 5 standard servos so would a 3A ubec such as this http://www.hobbyking.com/hobbyking/stor ... oduct=4319 work?

Thank you all for the valuable help
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Re: Hitec 311 potentiometer failure

Postby BillGriffiths100 » Mon Apr 22, 2013 4:05 pm

Might as well go for a five amp one:
http://www.hobbyking.com/hobbyking/stor ... Lipo_.html
Compromising with out of control government is like living with a lion, sooner or later the bloody thing will eat you .

You accept the tyranny of the state when it's not being applied to you, when it is: it's too late.
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Re: Hitec 311 potentiometer failure

Postby A.T. » Tue Apr 23, 2013 9:24 pm

A.T. wrote:For all analogue servos, including HS-311, suggest best compromise is to run a switchmode regulator at 5v
The higher the voltage, the higher the servo speed and torque and heat generated which also results in a much faster burn out
of components

It is possible that I was pushing the servo to it's limits in terms of its amount of travel (I battled to get the amount of throw that the ARF manual suggested). So maybe that coupled with the higher current led to the motor burning out?
Do you have any suggestions for "reliable" regulators? The plane has 5 standard servos so would a 3A ubec such as this work?
Thank you all for the valuable help[/quote]

Minimum 5A switchmode regulator for any Nitro/GP models, stay well away form linear regulators.
For a good proven unit and read
. Castle Creations CCBEC FAQ.
see also
. A beginner’s guide to switching regulators

Alan T.
Alan's Hobby, Model & RC FAQ Web Links
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