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Futaba FP-S128 servo.


David Davis 2
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Martin my issue was less to do with the specific argument about servo x with battery y and more an attitude issue. 

 

I see the british leyland 'that will do, it will be fine' bodge job attitude too much in modelling (this topic was the straw the broke the camels back in some respects) and it drives me up the wall. It wont be fine, it causes accidents and had caused fatalities in the past. I had a near miss testing engines here at work and it was a wake up call. Dont get complacent, dont get sloppy. 

 

Use the right gear, install it properly with the correct accessories, use the right fuel with the tank in the right place, the right battery etc. It extends further than that but you get my point.

 

Just do the job the best in can be done and take the whole thing seriously.  laughing and joking about the possibility of a serious accident, however remote, just puts my back up. Get real, get serious and do a better job. 

 

Grumble grumble, i need a beer. 

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On 13/08/2022 at 12:52, gangster said:

Something to bear in mind They will not tolerate 6volts strictly 4.8 volt max. Good servos I still have some

Not come across that - have several 128s that have been working for years on nimh 5 cell 6V packs and never noticed a problem. The 128s were also intended for use with 4X1.5V dry cells back in the day so I'm curious about issues  running them on 6V. 

Edited by Cuban8
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Curious, I used to have three 128 servos in a Junior sixty, which I sold in 2006 when I moved to France.

They came with a 1980s Futaba set I bought second hand in about 1990. 
So how old are these things?

As an ex plastics chemist I reckon the nylon will be ok, I think, not sure. Other plastic bits I’m not so sure about, they have plasticisers added when made, and some plasticiser migrate out over time, leaving a brittle component behind. 
Do electronic components also have a working shelf life, does a transistor remain as made?

Edited by Don Fry
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55 minutes ago, Cuban8 said:

Not come across that - have several 128s that have been working for years on nimh 5 cell 6V packs and never noticed a problem. The 128s were also intended for use with 4X1.5V dry cells back in the day so I'm curious about issues  running them on 6V. 

 

Oh lord here we go again. 

 

I have one of those dry cell battery boxes somewhere. I think i might stand it on the back fence post and shoot it with my air rifle just to purge it from the universe. 

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16 hours ago, J D 8 said:

 I got complacent recently, here is the result. Should have done a better job of checking control linkages on the old bird. 20years in a dry shed then one short flight.

Ezee Pzze.JPG

crash one ezee.JPG

 

Not as Ezee Pezee as you thought then 🙂   Mine also needs some repair after a too low approach, longer than I expected grass caught the undercarriage and tipped it in.  Nothing like as bad as yours though.

 

 

 

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              The Ezee Pezee flew well enough until the throttle linkage gave up and the Irvine 60 [ to much power for this plane ]  went flat out, resulting in a fast climb until a dot in the sky. Fed in a tad of down to try and prevent an out of sight situation but then found it was in a steady decent and no elevator control. On its final pass could see elevator fluttering like mad and only thing left was to steer to a "safe" shallow angle but speedy crash. Radio all worked afterwards. I had renewed the elevator servo for a modern one. Investigation showed plastic snakes had gone brittle.

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6 hours ago, Cuban8 said:

Not come across that - have several 128s that have been working for years on nimh 5 cell 6V packs and never noticed a problem. The 128s were also intended for use with 4X1.5V dry cells back in the day so I'm curious about issues  running them on 6V. 

5 cell nimh, nominal 6v, is nothing like the same animal as 4 dry cells, also nominal 6v, in a battery box. 

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5 hours ago, Don Fry said:

 

As an ex plastics chemist I reckon the nylon will be ok, I think, not sure. Other plastic bits I’m not so sure about, they have plasticisers added when made, and some plasticiser migrate out over time, leaving a brittle component behind. 
Do electronic components also have a working shelf life, does a transistor remain as made?

 

Heat cycles get them eventually. Take a long time though. 

 

Vibration can be an issue. Mainly in surface mount where the legs enter the packaging.

 

Resistors can drift in value. Some types very stable some less so. 

 

Capacitors will change value some types more than others. 

 

Servo circuit isn't massively dependent on the values staying exactly as per manufacture. Might get some drift in neutral positron over time I think. 

 

The feedback pot and motor brushes strike me as the most likely to fail parts. 

Edited by Nigel R
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That is arguably true, though a top quality alkaline cell can have a lower internal resistance than a mediocre NiMh cell.

Also, the most damage to the S128 servo in question will occur when it is the only servo being moved, not when multiple servos are moving together. This is when it will be supplied with maximum voltage (and therefore current). 

 

 

 

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2 hours ago, Nigel R said:

 

Heat cycles get them eventually. Take a long time though. 

 

Vibration can be an issue. Mainly in surface mount where the legs enter the packaging.

 

Resistors can drift in value. Some types very stable some less so. 

 

Capacitors will change value some types more than others. 

 

Servo circuit isn't massively dependent on the values staying exactly as per manufacture. Might get some drift in neutral positron over time I think. 

 

The feedback pot and motor brushes strike me as the most likely to fail parts. 

Semiconductors, especially silicon are incredibly reliable and rugged - including integrated circuits.  Many years ago I was involved in the design of short range radio telemetry used to measure temperature (via thermocouples) and vibration (via strain gauges) in gas turbines.  They were installed in the engine in an annular carrier and subject to at least 125 deg C and 20,000 g acceleration (plus vibration) and really the only failures were connecting wires to the transducers coming adrift during running.  The circuits were embedded in epoxy and the transmitters I designed were simply a pair of silicon transistors - very crude but the range was measured in millimetres (just as well because I was using Band 1 TV frequencies -40 to 80 Mhz 🙂 )

 

Resistors are reliable but capacitors less so, particularly aluminium electrolytics.  We used a lot of solid tantalum electrolytics which are very  good.  As Nigel says the main source of electrical problems are connectors, including ones like brushes or pots - ie, anything that moves or is moveable.

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1 hour ago, Gary Manuel said:

That is arguably true, though a top quality alkaline cell can have a lower internal resistance than a mediocre NiMh cell.

Also, the most damage to the S128 servo in question will occur when it is the only servo being moved, not when multiple servos are moving together. This is when it will be supplied with maximum voltage (and therefore current). 

 

26 minutes ago, Geoff S said:

Semiconductors, especially silicon are incredibly reliable and rugged - including integrated circuits.  Many years ago I was involved in the design of short range radio telemetry used to measure temperature (via thermocouples) and vibration (via strain gauges) in gas turbines.  They were installed in the engine in an annular carrier and subject to at least 125 deg C and 20,000 g acceleration (plus vibration) and really the only failures were connecting wires to the transducers coming adrift during running.  The circuits were embedded in epoxy and the transmitters I designed were simply a pair of silicon transistors - very crude but the range was measured in millimetres (just as well because I was using Band 1 TV frequencies -40 to 80 Mhz 🙂 )

 

Resistors are reliable but capacitors less so, particularly aluminium electrolytics.  We used a lot of solid tantalum electrolytics which are very  good.  As Nigel says the main source of electrical problems are connectors, including ones like brushes or pots - ie, anything that moves or is moveable.

Yes, I hear you. Now how much is that assumption. How many bits of machinery are still at work, that old. I bet the designer of the servo or component, if still alive, did not even consider the unit would survive him/her. And it’s in an aeroplane, take off an option, landing………

I don’t have these anymore, but I think I might retire them if I did. I’ve got a bag of 3001 units, the 148 have all got bearing slop, and gone. I don’t know how old, and I will use in hacks, but increasingly, I’m getting more suspicious. I know they have been mostly collected from debris fields, and the problem is, how many such wreck sites. Back then, these things were expensive. Gallon of fuel each?

Edited by Don Fry
Sorry, no idea how I copied Gary Manuel into the post. Idiot fingers.
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59 minutes ago, Martin Harris - Moderator said:

I would have thought the reference was to the 5 cell rechargeable battery going up to around 7.5v at full charge whereas a 4 cell dry battery might peak at around 6.2v when new - both nominally 6v....

The (my) point is that surely a 6v servo is designed to work from a nominal 6v battery, regardless of it's make-up. If not, then neither type should be used as they can both exceed the rated servo voltage. It makes no sense to regard the servo rated voltage as an absolute maximum.

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22 hours ago, Jon - Laser Engines said:

 

Oh lord here we go again. 

 

I have one of those dry cell battery boxes somewhere. I think i might stand it on the back fence post and shoot it with my air rifle just to purge it from the universe. 

I'm old enough to remember when people were getting all hot under the collar about converting their 'dry cell' pack outfits to the new AA size Nicads that were becoming available. Panic about the slight loss of voltage this time - to say nothing of alleged memory effect etc. A whole industry emerged on the back of that one with analyzers, cyclers, dischargers and conditioners to attract the lovers of gizmos. To say nothing of the pages of articles in the wide range of magazines available at the time, pre WWW, that left one usually no better informed.

Enough standard Futaba servos of the 128 type have been quite happily run on both 4.8 and 6v packs for decades now without a plague of problems - all my models have been run on 6V for thirty years without any sign of a problem with those Futabas. The exception has been a couple of cheapy micro servos that weren't happy and a particular type of Hitec that didn't want to centre very well on the 5 cell packs.

 

Edited by Cuban8
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fads and flavours of the month are common in aeromodelling in my experience, as is the drama and panic of anything new coming along and upsetting the status quo and, as you say, a slew of products to fix a problem that never existed. 

 

Does anyone remember mice? those add on exhausts that made your engine super quiet. They were in vogue for a short time when i was a kid. If i remember rightly, they worked brilliantly. The problem was, they worked by robbing your engine of all its power so were of questionable value! 

 

While not in a panic about all the new gadgets we have now, i do question the value of most of them and cant see that they really enhance my modelling experience. 

 

 

 

 

 

 

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3 minutes ago, Jon - Laser Engines said:

fads and flavours of the month are common in aeromodelling in my experience, as is the drama and panic of anything new coming along and upsetting the status quo and, as you say, a slew of products to fix a problem that never existed. 

 

Does anyone remember mice? those add on exhausts that made your engine super quiet. They were in vogue for a short time when i was a kid. If i remember rightly, they worked brilliantly. The problem was, they worked by robbing your engine of all its power so were of questionable value! 

 

While not in a panic about all the new gadgets we have now, i do question the value of most of them and cant see that they really enhance my modelling experience. 

 

 

 

 

 

 

Aay, these new fangled electric motor thingies 😉

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