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HelicopterMain Discussion › Throttle servo end point
02-17-2018 06:26 PM  66 days agoPost 1
Felino

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Mexico city

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I replaced an old Align DS620 throttle servo wit a Futaba 9254 and I had to increase end point from 100% to 120% on both sides.
In other words the Futaba servo needs more end point travel than the Align servo.
Any one knows why?
Is it normal?

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02-17-2018 07:17 PM  66 days agoPost 2
Flyin for Jesus

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Troy, IL. 62294

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Did you use the same servo arm?

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02-17-2018 09:06 PM  66 days agoPost 3
Jeff polisena

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westpalmbeachflorida usa

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Many things could cause this , servo gears , pulse width design etc . Might have to move ball on servo arm to get numbers you want . Nothing strange being that you are talking two different servos .

I stole it ,flew it and gave it back ;)

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02-18-2018 01:20 AM  65 days agoPost 4
Felino

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Mexico city

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Yes, I am using same lenght servo arm.

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02-18-2018 04:31 PM  65 days agoPost 5
Andy from Sandy

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Bedfordshire, UK

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Any one knows why?
Is it normal?
This is normal in my experience with Futaba servos but I don't know why. I think it could mean it has a better resolution than the Align servo.

Not just the 9254 but other tail servos like BL276 and MKS890 both do the same.

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02-18-2018 05:25 PM  65 days agoPost 6
wjvail

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Meridian, Mississippi

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Isn’t the 9254 a tail servo? Am I confusing myself again.

"Well, Nothing bad can happen now."

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02-18-2018 05:31 PM  65 days agoPost 7
Andy from Sandy

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Bedfordshire, UK

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It is but a lot of people use it on the throttle as it is very easy to move when unpowered and can be driven with a spring for auto throttle shut when the supply to it fails.

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02-19-2018 02:58 AM  64 days agoPost 8
Jamovich

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Bangalore, India

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It also dies quickly because of direct engine vibrations!

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02-19-2018 02:20 PM  64 days agoPost 9
JLF92677

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Southern California

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Jamovich
Jamovich
It also dies quickly because of direct engine vibrations!
Pls explain why this servo is affected by “direct engine vibration” and not others?

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02-19-2018 02:37 PM  64 days agoPost 10
Jamovich

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Bangalore, India

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Because it is meant to be a tail servo and isn’t tolerant of the vibrations that go from the throttle lever (which are definitely higher).

I have had 3 fail when used as a throttle servo.

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02-19-2018 02:50 PM  64 days agoPost 11
Jeff polisena

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westpalmbeachflorida usa

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I don't think its vibrations that make them fail but the short pulse .Servo will heat up and heat makes them fail . When tail servo is on tail yes there is loads but not as much radical change being processed from gyro and stick . The control of gov and stick movement processed to servo on throttle the load in constant and on tail there is not when correctly setup and stable . I would recommend using same throttle servo as cyclic or faster cyclic servo instead of tail servo . The throttle servo will stay ahead of cyclic because of a lesser load . Tail servos are more costly and will fail every time on throttle . I believe leverage would be more of the reason than vibrations.

I stole it ,flew it and gave it back ;)

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02-20-2018 06:17 AM  63 days agoPost 12
JLF92677

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Southern California

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Jeff Polisena
Jeff polisena
When tail servo is on tail yes there is loads but not as much radical change being processed from gyro and stick . The control of gov and stick movement processed to servo on throttle the load in constant and on tail there is not when correctly setup and stable .
Difficult to buy this answer. There is virtually no throttle servo load to speak of when rotating a carb barrel, certainly not compared to the load when changing tail rotor pitch constantly driven by main rotor torque demand change. In as far as servo duty on throttle application, if a rudder servo can’t take said duty, then it can’t take rudder duty. Unless you have hard log servo data to support this theory, I find it hard to buy it.

I suspect the servo failure problem has to do with receiver battery pack voltage. What RX battery voltage are you or others using that have experienced S9254 failure?

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02-20-2018 08:16 AM  63 days agoPost 13
Jamovich

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Bangalore, India

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4.8 volts (this was back then during the hirobo flybar days )

The vibrations experienced at the throttle barrel are different than from the tail. If I only lost 1 servo that was probably bad luck...but 3 there is something else going on

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02-20-2018 10:16 AM  63 days agoPost 14
ICUR1-2

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Ottawa, Ontario

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I remember this discussion from years ago . Having a fast carburator is only as good the engines reaction time to different loads.
Don't waste you're time here instead of .Focus on a reliable servo.

spending time, paying attention

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02-20-2018 10:20 AM  63 days agoPost 15
ICUR1-2

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Ottawa, Ontario

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Got an idea to set up my helicopter with a rc car throttle
Style.

spending time, paying attention

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02-20-2018 07:24 PM  63 days agoPost 16
JLF92677

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Southern California

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JAMOVICH
Jamovich
4.8 volts (this was back then during the hirobo flybar days )
What exactly do you mean by above statement? Whether it is back then or today, S9254 servo spec has not changed, it is a 4.8V servo, period. If you are using a 2S LiPo, LiFe, Li-ion or 5 cell NiCd or NiMH you then have the most probable answer to your problem.

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02-21-2018 02:17 AM  62 days agoPost 17
Jamovich

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Bangalore, India

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Meaning using 4.8v servos and 4 cell nimh packs. Today everything is HV

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02-21-2018 05:56 PM  62 days agoPost 18
Richardmid1

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Leeds, England

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You will simply need to use a longer servo arm on the 9254 as governors generally say to get as close to 100/100 as possible.

As for vibration, the linkage isn't solid so vibrations to the servo through the linkage will be minimal, you can however mount the throttle servo 'softer' than you would a cyclic or tail servo. You can remove the brass inserts from the rubber grommets and don't overtighten the screws.

The throttle servo will fail quickly if you haven't set the limits correctly allowing the servo to bind at full closed or full open position. Carb barrels can occasionally bind or become stiff which would also burn a servo out. 9254's have been used as throttle servos for a long time, not because they move freely when unpowered as someone mentioned but because they work just as well with governors as they do with tail gyros due to their extremely fast reaction and transit times. Remember, increasing engine rpm takes some time (Although once upto speed changes are extremely fast in our small nitro engines) BUT we are talking about the engine changing torque output to maintain HS which at 16,000 rpm happens ever 0.00375 seconds! Pretty immediate.

60% of the time, it works every time!

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HelicopterMain Discussion › Throttle servo end point
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