JR 8425 Digital servo - uses?

[malc1]

Hi
Is anyone using the DS8425 Digital servo on their helis?
I`ve managed to hold of a spare one from a friend and was wondering whether I could use it as a rudder servo on my scale Vario heli.
( I`m using DS 8231`s on the head)
The thing is JR seem to say that it is for aircraft only.
Why when the spec seems to be so good?
:dontknow

[Coolice]

Hey,

Really and truly it's a little slow for use on a tail rotor, having said that on a scale machine your not looking for 3D olding power and lightening speed either. But will the speed of the servo mean you will have to run less gryo gain as the slow speed will not allow it to keep up to well with torque changes? I am inclined to think this will be the case.

A few years ago now I was running JR8311's in my Century Predator and I then came across reports of them being for aircraft use only. Anyhow I was still running them but one did fail and the replacement I got then got given stated on the packaging for aircraft use only. By this time is was more known that they were for plank use.
The reasonoing behind this is that the servo is not designed to handle the higher vibration levels of a helicopter. In thoery as you say the specs are very good for heli use, but it is their tolerance to vibration that is different.
I think a lot of the recommendation is based on flight testing in models and seeing what servo's lat longer in the different environments.

You dont say what gyro you are going to be using, if it's Futaba I'd suggest a better servo more suited to the tail control.
.

[malc1]

Hi Ian
I`m going to use a JR 490T gyro with the Vario.
Maybe I ought to put this DS8425 I`ve got on the throttle and get a 8700G for the tail.
Possible to tame things down a bit with the radio maybe?

[Coolice]

Hey,

Is this Vario going to have a fenestron tail rotor? If so I'd check if your ok using heading hold or not as I have heard it's advised not to.
You may not be going to use a fenestron but I had to ask incase.

It will certainyl be good on the throttle, overkill perhaps but atleast if it stops working there you can still get the model down ok.
As you have mentioned already the specs on most of the top spec servo's is very good, but if they cannot stand the vibration levels in a heli environment then the risk isn't worth taking. I nearly lost a model through the 8311's I had fitted in the past.

The 8700G will be perfect for the tail, this servo is one of the best. Perhaps not the fastest available nowadays but a great servo nethertheless.

As for taming the tail down, I think this gyro works like a GY401 in that a pot on the gyro itself is used to limit the servo travel and hence not cause binding of the tail slider. Try to keep this above 100% and use a shorter servo arm if need be though. Then the transmitters ATV/EPA on the rudder channel is used to alter the pirouette rate, eg. move travel for a fast piro or less for a slower one.
I have not used a 490T and so cannot be more accurate but I think this is the case. Someone may jump in and be 100% confident as they use/used a 490T.
.