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potentiometer gone dead

Old 12-17-2006, 04:49 PM
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PlagueWielder
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Default potentiometer gone dead

Hey guys,

I have an almost brand new mini metal geared servo (similar to the hitec 81MG or 85MG). It has flew around 4-5 times on the plane (29% Giles with an OS 1.60). The engine is soft-mounted to reduce shaking.
Anyway, yesterday I turned the plane on and the servo started to dance where ever I put it at... simply the potentiometer got screwed up. I tried other servo slots and it was the same.

Anyway, what do you guys think caused it? Could it be a bad servo? Servo linkage not good (metal pushrod)...? I had a standard servo (3004) there before with the same linkage and it was fine for a lot of flights.

Thanks

Eliraz
Old 12-17-2006, 06:20 PM
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JGspeed
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Default RE: potentiometer gone dead

Well you already determined the servo is bad, so the questions are why did it fail and should you fix it. You didn't mention the brand so I'll assume it's an off-brand. I've got a box full of cheap "off-brand" servos that experienced failures with very short life.

Your description of the problem sounds like it's pot related and a cheap servo will be using cheaper (less reliable) components. Since you're flying something that big, I'd go back to the 3004. It would be a shame to waste a plane on a problem that could have been avoided by fixing something that wasn't broke.

The soft mount might keep engine vibration from the airframe, but if your linkage is solid it's still coupled to the servo. The metal gear may have helped wipe out the pot depending on how the pot is mounted.

If you had a good reason to go to the smaller servo, try a better servo. I like Futaba 3101's since I come from a sailplane background. Their only weakness is the strength of there plastic gears. That can be fixed by boiling the gearset for 10 min to balance any stresses from the molding process (but don't fly them under 20 deg). Even though the throttle servo is the least dangerous to have fail, in a Giles at 29% that could still be dangerous.

Good Luck and soft landings
Old 12-18-2006, 01:36 AM
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PlagueWielder
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Default RE: potentiometer gone dead

Its a GWS servo (Micro 2BBMG to be exact) and its not that "off brand", people here use it for a lot of things even bigger.

What's more sensible? That the servo was bad or that the hard linkage did it?

Thanks
Old 12-18-2006, 09:05 AM
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tkilwein
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Default RE: potentiometer gone dead

Are you using a small mini-micro servo on a 29% scale? A little small for me.

Would vibration be a culprit? I have-had some GWS servos and vibration killed them, in a small gas plane.

I only use GWS in the foamies now.
Old 12-18-2006, 09:26 AM
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PlagueWielder
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Default RE: potentiometer gone dead

Its not a mini micro... its mini or micro (not both lol..). It is similar in size to the Hitec HS 81MG or 85MG...

What's more likely - a bad linkage or a bad servo?

Thanks
Old 12-18-2006, 10:12 AM
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davewallace
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Default RE: potentiometer gone dead

PlagueWielder,
It has been long establish that the small servos don't holdup on the large gas planes. If the pot is direct drive, the vibration must have damaged the pot. Anyway, it happens a lot and the fix is a larger servo.

Dave

Old 12-18-2006, 10:55 AM
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PlagueWielder
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Default RE: potentiometer gone dead

Alright, thanks.
Old 12-18-2006, 10:59 AM
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Default RE: potentiometer gone dead

Eliraz,
Even a "standard" servo would be marginal on a 29% 1.60 power plane, a mini is unthinkable for ANY control surface in that class, unless we are talking about the throttle
Pete
Old 12-18-2006, 11:34 AM
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PlagueWielder
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Default RE: potentiometer gone dead

I am talking about the throttle servo, sorry for not mentioning this VERY important piece of info...

I'd never put that small of a servo on a surface, not even on a .46 plane.
Old 12-18-2006, 11:57 AM
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Default RE: potentiometer gone dead

Hi Eliraz,
OK that's better
I would imagine that the servo may have been a "dud", but I would be inclined to go back to a "standard" servo, if for no other reason than they are cheaper and more durable than a mini servo, and weight should not be a factor for that plane.
Good luck,
Pete

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