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Any downside to micro servos?

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Old 06-16-2007, 06:29 PM
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garywi
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Default Any downside to micro servos?

I have never bought one before. If I can find a metal geared micro with 60oz of torque at 6v with bearings, with a tiny case, what is the downside?

I am looking to use to mount externally on a Sig Kadet.

The only thing I can think of, the micro's have only two mounting screws, instead of four and you may ripp the servo out of mount?

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Old 06-16-2007, 08:01 PM
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Default RE: Any downside to micro servos?

I think I would have to know the exact servo and application to form an oppinion. All I can say for now is "maybe".

Why do you want to do this?
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Old 06-16-2007, 08:23 PM
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garywi
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Default RE: Any downside to micro servos?

Thanks Bruce. Trying to save weight in a Kadet.

G
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Old 06-16-2007, 08:52 PM
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Default RE: Any downside to micro servos?

Just use standard servos. Unless you need to save weight so you can carry something else there is no need to save weight like this on this plane.
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Old 06-16-2007, 09:12 PM
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Default RE: Any downside to micro servos?

Try some in non flight critical applications and see how well they stand up under the vibration generated by the engine.

My past experience has not been favorable using the micro and minis around gas and glow engines. I don't know whether it is the small electric motors or something else on the circuit boards but I have had a half dozen failures all occuring in a 5 to 20 minute time span. All were on throttle and retract air valve applications.
ORIGINAL: garywi

I have never bought one before. If I can find a metal geared micro with 60oz of torque at 6v with bearings, with a tiny case, what is the downside?

I am looking to use to mount externally on a Sig Kadet.

The only thing I can think of, the micro's have only two mounting screws, instead of four and you may ripp the servo out of mount?

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Old 06-16-2007, 09:30 PM
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Default RE: Any downside to micro servos?

The minis may have the torque, gear train and speed to handle your requirements but few, if any of the minis can handle the vibration.
Small motors, small traces = poor vibration characteristics. All brands.
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Old 06-17-2007, 02:50 AM
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Default RE: Any downside to micro servos?


ORIGINAL: garywi I have never bought one before. If I can find a metal geared micro with 60oz of torque at 6v with bearings, with a tiny case, what is the downside? I am looking to use to mount externally on a Sig Kadet. The only thing I can think of, the micro's have only two mounting screws, instead of four and you may ripp the servo out of mount?
Why 60 oz torque on a Kadet unless the model is grossly out of balance? even 33 ounze at 4.8v has been more than adequate for past 25 years.
Micro servos and recent mini servos were designed for the new generations of ultra lightweight park flyers, 1/2A etc and whilst they have the torque, the teeth simply do not have the "shear" factor required and as imposed on the gear train by shock loads of GP models. Smaller servos have lighter circuit boards, pots anmd other components which also suffer under the vibration of GP motors. Rule of thumb is to fit the servo with the thickest possible gear set and largest case practicable for size of model, especially if weight difference is minor. When next near LHS, wander in and examine the packets of gears sets and see how very thin the gears get as the servo gets smaller and remember metal gears wear out and get sloppy much much faster than nylon. A hard landing may flap the control surfaces enough to shear a thin gear tooth with a premature end to next flight - jammed servo gear (gitching / loss of control) often blamed erroneously on TX or RX failure..
Refer 101 - Servo FAQ & picking the right servo for the job and the many articles on my web page relating to servos.

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Alan T.
Alan's Hobby, Model & RC FAQ Web Links
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Old 07-19-2007, 05:59 PM
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Default RE: Any downside to micro servos?

better off to get a cheaper standard servo than one of those micros that actually cost more and do not last half as long due to the vibration chipping the teeth on the gears.
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