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Futaba FP-S128 servo.


David Davis 2
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Years ago I bought a 1/6 scale BE2e from a bereavement sale. It is fitted with Futaba FP-S128 servos. So far they have always worked well on the few occasions each year when the weather is suitable for flying the BE2, but I'm not familiar with these servos. Does anybody have any experience of using them?

 

How do they compare to the better-known S3003 or FP-S148 servos?

BE2e Sunday 9th April 2017 No 1.php (Small).jpg

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Last winter I went through my old servos [ all Futaba ] All still worked ! Oldest [ exposed 3 pin connectors ] are An Fd33, FD 32 even an FD16m  but compared to say a 148 rather slow in end to end travel, the FD16 might just beat a snail over the distance travelled :classic_biggrin:.

  In a WW1 type like the BE2C who's control response will not be quick anyway so the 126's will be fine as long as travel is smooth with no glitches I recon.

 

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I have some 128's still working well.    But I would suggest changing the elevator servo to a newer one just in case.   An elevator servo failing will be a disaster but anything else failing might be recoverable with some skill and luck. A 148 or 3003 will fit easily in place as they are slightly less deep.  

Edited by kc
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19 minutes ago, Paul De Tourtoulon said:

Why , they were sold in radios with battery boxes for  4 x 1.5 battery's, I have a couple of Futaba servos S 9404 these are 4.8v and also some Graupner ones are printed  with 4.8v on them.

 

I am curious Paul, do you read the instructions for your equipment just so you can do the exact opposite? 

 

If a servo is recommended to operate at 4.8v only then operate it at 4.8v. Like it or not the servo manufacturer knows more than you and they guarantee reliable operation of the servo on 4.8v, taking into account a fully charged 4.8v pack is likely to be 5.5v. If they do not recommend 6v packs there must be a reason for that, so dont try to be clever, just do as they tell you.

 

Were your model to crash due to servo failure when running excessive voltage then you would be liable for any damage or injury caused as you are running the thing out of spec. Needless to say this could land you in prison pretty quickly if it is proven the failure of the servo was caused by excessive voltage. And lets be honest, the servo manufacturer is unlikely to step in a save your bacon by accepting liability themselves. 

 

Model flying is not a game and a failed servo could have fatal consequences so i dont buy into the 'ahh it will be fine' approach to something like this. Run your servos at the manufacturers recommended voltage. 

 

 

 

 

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Wake up Jon,,,I sold and used servos since my first single channel Mcgregor, they had a battery box for four 1.5 battery's ( did you read my post ? )

Graupner and a few other radios had a 4.8v deac and other rechargeable battery's, as said in my post that Graupner servos had them stamped 4.8v on the servo supplied with these radios (I still have some ) the only 4.8v Futaba servos that I have used ( and still have in my wren powered Rafale ) are Futaba S 9404, they did also do a fast tail rotor one for helicopters as I had one, almost of the others were for 4.8/6 volt use. with the exception of a few oddball ones,.

 

 Google Futaba data base just to prove me wrong,,,😉

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Selling and using is not the same as designing and testing so perhaps it is not me that needs to wake up. 

 

I have read everything you have said and you are missing the fundamental point. 

 

If they recommend 4.8v and/or supply a radio with a given set of servos and battery etc, then that is what you use. Trying to napkin math 4x1.5v in your battery box to mean its ok to run a 6v battery simply dosent work as the 5 cell pack most consider to be 6v runs over 7v when fully charged. While i do not have any AA's in the house i have some AAA and 9v batteries new and in their packet. Measuring both they read on average .1v/cell over the rated 1.5 with no load. So your battery box is going to be 6.4v fully charged with no load and i used to see 6.2 on new AA batteries in my dx6i. This is still lower than the fully charged 5 cell and the additional voltage may cause damage or lead to premature failure. I have seen it happen. 

 

But seeing as battery boxes are a dead technology anyway we can consider them irrelevant. 4.8v is used to represent 4 cell and 6v represents 5 as these are probably 5.5 and 7.2 respectively when fully charged. My TX battery is a 9.6v and yet i have seen it hit 12v just after i whip it off charge. It rapidly falls off to the low 11's. This is true for a lipo as well with 11.1v 3s's being about 12.6 when charged. The point is, the actual voltage is not the rated voltage and the designer has taken this into account along with a  bunch of factors and has decided that a 4.8v 4 cell battery is the one for the job. If that is what he decides then that is what you use. 

 

Anyway the problem i have Paul is not so much the specific discussion about the 128 but that your attitude  more broadly to the subject.  It comes across as just going for it and hoping for the best while completely disregarding the instructions from the manufacturer and the potential consequences because you think you know better. Unless you designed that servo, you dont know better.  If you have a piece of equipment where an operating voltage is specified then you stick to that voltage because the manufacturer wouldnt have specified the voltage as 4.8 only if it didnt matter.

 

And incidentally, a friend is a trained futaba service and electrical engineer so i double checked my rationale with him to see if i was being unreasonable. He confirmed that overvolted servos die prematurely and often without warning especially if they are stalled by accident. The 9404 you mention was one he specifically pointed out as being vulnerable and that its a very bad idea to exceed the voltage specs listed. He also pointed out that throughout the time he was dealing with futaba gear all of the radios sold came with a warning not to use dry cell battery boxes because there was a risk of over volting. 

 

 

 

 

 

 

 

 

 

 

 

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Quote,,

 

 

Selling and using is not the same as designing and testing so perhaps it is not me that needs to wake up.

 

so designing and testing Futaba radios was done in England ?.

 

Does testing include fitting the 4aa battery's to the receiver 8 to the transmitter checking the servo throws and explaining the radio to a customer 5 times a week ( at least ) for 20 years count.

 

 No, a lot of radios in France Graupner, Futaba and Multiplex, I was an agent for these three makes were sold with battery boxes,

ALL the 2/3 channel Graupner and Futaba radios were sold with battery boxes and the Futaba 'car packs' which included 1 litre of Robbe Roktan  5% castor mix ( oh dear here we go again ) and 12 AA battery's

 

Ps Futaba France is 90 klms from me I went most Monday mornings to pick up stock and have chin wag while repairs to radios and other gear was done, a coffee and later lunch with the staff the two Futaba technisions included, paid for by the boss,,, Mr Tourniere.

 

Just for the fun, Here is a picture of one of my old shop catalogues with the FC-18 and battery box,

 

 Sorry if it has come to a 'pillow fight',,,,

 

Signing out better things to do,,,

20220813_205605.jpg

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This isnt a pillow fight Paul, you are wrong and that is the end of it. I am simply trying to explain why in the hope that you might learn something. It didnt worth castor oil, but i have to try. 

 

The design and test was done by the various brands wherever they do their development. They then set the rules and provide technical documentation and training to their support staff. The guy i know was one of the trained futaba support staff and is a trained electrical engineer. He is more qualified than i am to comment on the granular detail of why its a bad idea, but i know enough to know its a bad idea as i studied electronics as well just not to the same level. 

 

You sold radios, collected radios, fitted batteries and ate lunch. I dont wish to be disrespectful, but that does not qualify you to comment on them from a technical point of view. You simply dont have the required expertise. Also the radio in your photo looks older than i am. 

 

We all drive cars, they come with requirements for fuel, oil, tyres and load carrying set by the manufacturer. Full size aircraft come with limits for dive speed, stall speed, g force loading etc, your washing machine has a limit on the weight it can carry and even the kettle has a limit on how much or how little water you can boil to prevent damage. Mechanical things have limits, set by their respective manufacturers and its very rare that an end user knows more about it than the people who designed and built it.

 

Running 4.8v rated servos from any brand at more than the equivalent peak voltage of a 4 cell nimh pack is wrong. There is nothing you can say that makes it right. if you think it is a good idea to ignore the specific and clear instruction from the manufacturer and risk a potentially serious accident caused by a failure of that piece of equipment then there is no hope for you at all and i am glad you dont fly anywhere near me. 

 

 

 

 

 

 

 

 

 

 

 

 

 

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One of the biggest problems I had when working was caused by technicians having a closed mind mentality. Apparently, many people will draw conclusions from a one-off event which results in a work around that they will obstinately stick to for the rest of their lives, when challenged they quote supporting evidence and completely ignore everything that proves them wrong. 

 

Is an ancient old Tx system relevant to the present situation Paul?

 

There are many posts on here stating that servos are run at higher voltages than the manufacturer recommends with no detrimental effect, I wonder how many failures are attributed to something other than overvoltage. Just because others do something doesn't mean it's a good idea but unfortunately there is a herd mentality where many will follow the example of whoever talks longest and loudest. 

 

6 hours ago, Jon - Laser Engines said:

Running 4.8v rated servos from any brand at more than the equivalent peak voltage of a 4 cell nimh pack is wrong. There is nothing you can say that makes it right.

 

👍

 

Steve

 

 

 

 

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I had 4.8v rated servos in an ESM Hurricane powered by a 4 pack NiMh. I hadn’t charged the batteries before flying so after one flight I replaced the power supply (without thinking) with a 2s LiFe. Next flight took off as normal, banked and it ploughed the ground. Upon investigation aileron servos had failed. 
 

Moral of the story, don’t listen to so called experts who think they know better, stick with what the manufacturer specifies.

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Thank you gentlemen for such interesting and informative responses. In the event yesterday's flying session was something of a wash out. I did not build this model, as I explained in the original post, I bought it in an estate sale. To replicate the real aircraft's external cables running to the rudder and elevator there are two short pushrods operating bellcranks which move the scale external bellcranks. The gentleman who built the model used a normal steel clevis at one end of the pushrods and a plastic clevis on the other end, the type which has a small brass screw coming in from the side. We found out at the flying field yesterday that the little screw was no longer tight against the pushrod and that as a result I had no elevator travel. Just as well we found the problem while the model was still on the ground! I propose to change the pushrods and make up a Z bend on one end and use a steel clevis on the other. This will involve removing the lower wing at least and to do this I will have to undo six bolts and twelve cables so I've set that job aside for the moment.

 

Regarding the use of 4.8 or 6 volt NiMh batteries I am aware that some Futaba servos prefer 4.8 volts, ( four cells) and that there have been reports of 5 cell batteries destroying servos. I have read a spec sheet of the FP- S128 which states that the servos are good for 6 volts but, as has been posted above, this may refer to the later servos and I don't know how old mine are. I am not sure whether I have a 4 or 5 cell NiMh in the model but it has flown satisfactorily for at least seven years albeit only three or four times a year. Because I'm going to have to take the model apart to replace the elevator and rudder pushrods, there's not much more work involved in checking the rx battery. If it is a 5 cell battery I will replace it with a 4 cell battery just to be on the safe side. I have a couple of sound 4 cell batteries which will do the job and I can use the 5 cell battery in another model. 

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If you are ok with  4.8v go for it, 6v will only give you more speed and power that most applications won't warrant, 5 cells is a small security if the accus are old and one dies on you in the air.

 

 

It's ok jon I also built my own radios, receivers servo amplifiers and repaired cb and boat radios,   that was a long time ago but volts are still volts,,,

 

 It feel like I am standing on the side of a boat relieving myself against the wind,,,,🙃

 

sorry but if offended can the last remark be struck out by the moderators,,,

 

 

Edited by Paul De Tourtoulon
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2 hours ago, David Davis said:

Regarding the use of 4.8 or 6 volt NiMh batteries I am aware that some Futaba servos prefer 4.8 volts, ( four cells) and that there have been reports of 5 cell batteries destroying servos. I have read a spec sheet of the FP- S128 which states that the servos are good for 6 volts but, as has been posted above, this may refer to the later servos and I don't know how old mine are. I am not sure whether I have a 4 or 5 cell NiMh in the model but it has flown satisfactorily for at least seven years albeit only three or four times a year. Because I'm going to have to take the model apart to replace the elevator and rudder pushrods, there's not much more work involved in checking the rx battery. If it is a 5 cell battery I will replace it with a 4 cell battery just to be on the safe side. I have a couple of sound 4 cell batteries which will do the job and I can use the 5 cell battery in another model. 

 

Thanks to Ron this is the important bit of information from the manual.

 

image.png.8d2aaf4e72d62bfcb6fd0989d99ff7aa.png

 

Odd that 6.0V is ok if shared with the receiver, I guess there must be a reason.

 

Steve

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1 minute ago, Gary Manuel said:

It means the power supply is shared with the receiver (regardless of voltage used).

I read it as 4.8V or 6.0V when shared with the receiver. In other words, 4.8V if not powering the receiver but 6.0V if it is also powering the receiver.

 

Not to worry.

 

Steve

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19 minutes ago, David Davis said:

What's a regulated supply?

From a UBEC or ESC using a two cell Lipo battery for example.

 

From what I have read a four cell NiMh pack should be used if it's not supplying the RX. If supplying the Rx a five cell NiMh can be used because when the Rx is switched on the voltage will drop to acceptable levels. However, with a regulated supply the voltage will be maintained at 6v when the Rx is switched on, which is not good for the servos. Which takes us into disputed territory as some say it works fine and others say it's not in accordance with the manufacturer's specification. Not a problem in this case as NiMhs will be used.

 

This is my understanding from what I have read, confirmation would be good.

 

Steve

 

 

 

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