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Old May 26, 2014, 11:06 AM
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USA, WA, Bremerton
Joined Feb 2007
851 Posts
Question
4.8v Servo - Step-down from 5.5v source

A flying buddy and I use YEP esc's on our heli's. These output only 5.5 volts. The Futaba S9257 tail servos operate at 4.8v only.

On another heli I run a separate 5.0v ubec which has worked ok.

If we use a step-down type regulator it will bring the voltage down to 4.7 under no load. Will this work or are we asking for problems. The unit we are considering is: http://www.western-robotics.com/STVR_hp.html

Are we being to worried about the voltages or what.

Any guidance would be appreciated.
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Old May 26, 2014, 11:39 AM
AndyKunz's Avatar
Illinois
Joined Sep 2001
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Quote:
Originally Posted by Blade Crasher View Post
Any guidance would be appreciated.
Use a better tail servo then.

Andy
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Old May 26, 2014, 11:50 AM
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USA, WA, Bremerton
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Why, when that servo has more capability than I will ever have at my age, hand-eye coordination and flying desires.

Thanks for your input though.
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Old May 26, 2014, 12:01 PM
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United States, TX, Leander
Joined Sep 2003
2,720 Posts
You could get away with running a serial diode to drop the voltage a little. I had to do that recently for a JR791 retract servo. I just upgraded to life packs and put the servo on a regulator. But one out of three servos still acted up. I put a diode in series with it and dropped the voltage enough to get it to straighten up.
Edwin
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Old May 26, 2014, 12:42 PM
AndyKunz's Avatar
Illinois
Joined Sep 2001
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Quote:
Originally Posted by Blade Crasher View Post
Why, when that servo has more capability than I will ever have at my age, hand-eye coordination and flying desires.
The only reason I suggested it is because you're looking at adding components (weight, possible failure points) to your model. If you have a servo on there which will run at 6V (any modern servo will) then why limit yourself with a servo that doesn't measure up to the rest of the system?

Also, why do you think that servo only works at 4.8V? I would investigate that as well. There's a guy here named "Bax" who runs the Futaba service stuff. You ought to PM him and ask if that servo will run on a 6V system. My guess is that it will, but you need to go straight to the horse.

Andy
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Old May 26, 2014, 01:29 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
Joined Oct 2007
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Servos voltage sensitivity is tricky.
some are- some ain't
I have a model which came with servos intended for 5.3/5 volt output from a BEC
on 6.5 volts they really performed but some refused to operate at 6.6!
I ran rapid full excursion tests at 6.2volts and found that they overheated in 4 minutes and the motors went boom!
Being a timid soul- I won't run any of the servos which are intended for ARF 5.4 volt , at anything over an absolute 6.000 volts
maybe ona glider which cruises lazily - but never on a copter or aerobatic model which does a lot of fast servo reversing.
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Old May 26, 2014, 01:47 PM
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United States, TX, Round Rock
Joined Dec 2004
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This is what i use on a T-Rex 600E with Futaba S9254 on the tail and the stock BEC. The S9254 is the "bigger brother" of the S9257.
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Old May 26, 2014, 04:50 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
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Ihave one of those plus the ALIGN 7.4 to 6 voltvoltage reg which came as a package - . anybody need one ?
never used just checked out on the bench when I was considering regulators - works fine.
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Old May 26, 2014, 11:01 PM
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USA, WA, Bremerton
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Thanks again to all that posted.

Since I own the 9257 - that was the reason of sticking with 4.8. I will try to find Bax though and see if he has any different info.
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Old May 27, 2014, 11:12 AM
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The Northeast Kingdom, Vermont
Joined Jun 2004
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Have you tried that servo at 5.5V, it should work. That servo it designed to run on a 4 cell Nixx pack, not 4.8V maximum. A fully charged 4 cell battery will be at least 5.6V to 5.8V.
Pete
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