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Is there a new breed of servo ?

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Tim Ballinger08/03/2020 13:33:03
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778 forum posts
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Choosing servos is something I always seem to agonise over and it never seems to get any easier. Last discussion on which servo I can find was started by Tim Macky some 10 years ago but we now seem to have a new breed of micro/ mini digital servos on the market at very competitive prices ie under £10.
They claim to offer 3 - 3 kg.cm torque which puts them right in the pocket for the 3-4 lb sport model. Current draw never seems to be quoted but difficult to believe at this size that they are in the area of troubling our power supplies.

Durability? Well they come with metal gears and I am yet to see anything negative written.

In the 5 years I have been back in modelling I have only had 1 servo actually fail , a 17g cheap (analogue) Chinese version that came with model.
The rest are still going strong. Despite this, for my builds, I still tended to opt for standard size and or better known makes where space/budget permitted.

I recently tried the cheap micro digital variety in a Mini jet. Too early to tell if they will last but makes me think seriously about the mini versions for my next model.

I guess what I am seeking opinions on is ; is it still valid to pay 2- 3 times the price for what was once seen as a quality servo when these new cheap, mini digitals are on the market.

Tim

john stones 108/03/2020 13:42:08
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11455 forum posts
1516 photos

You get what you pay for ?

This has long been the go to response, it was quoted when the likes of Frsky brought out "cheap" RXs TXs, yet they stood the test of time and increased their customer base.

Servos ? There's loads now, always nice when a user gives a recommend though.

Don Fry08/03/2020 15:07:30
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4557 forum posts
54 photos

The Futaba 148 servo came out about 40 years ago. Nothing wrong with them. I've got some older Multiplex servos, between 60 and 80 grams apiece. Much the same power as the 148.

Times move on. I mostly run IC.

20 gram High Voltage Corona units, 4.5 Kg, and 6 Kg 30 gram, run off a 2 cell Lipo, will go into the 160V powered XtraWot next up to be built.

Dickw08/03/2020 15:25:14
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671 forum posts
95 photos
Posted by Tim Ballinger on 08/03/2020 13:33:03:

......................
They claim to offer 3 - 3 kg.cm torque which puts them right in the pocket for the 3-4 lb sport model. Current draw never seems to be quoted but difficult to believe at this size that they are in the area of troubling our power supplies.

................................

I recently tried the cheap micro digital variety in a Mini jet. Too early to tell if they will last but makes me think seriously about the mini versions for my next model.

I guess what I am seeking opinions on is ; is it still valid to pay 2- 3 times the price for what was once seen as a quality servo when these new cheap, mini digitals are on the market.

Tim

Like you I have just installed some cheap micro digital servos in a mini-jet and am quite comfortable using this sort of servo in sports models. I expect a reasonable performance and life.

For my much more expensive 1.6Kg 180mph 2m electric gliders I use KSTX08 servos throughout as I am prepared to pay a lot more in the hope of a better long life performance, particularly as they are "moulded in" so replacing them requires major surgery. So far they have been good for 100s of flights at high G loads.

"Horses for courses" really, and some of the cheaper servos are surprisingly good.

Dick

Ron Gray08/03/2020 15:26:37
1931 forum posts
803 photos

A lot will also depend on if you want precision, eg for aerobatics, where spot on centering is a must.

Tim Ballinger08/03/2020 15:33:46
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778 forum posts
283 photos

Ron ,

interesting comment re centering. I get the feeling that the new cheaper digital servos would be better at precision centering and holding than a similarly priced or even more expensive analogue.

Tim

Edited By Tim Ballinger on 08/03/2020 15:34:04

Erfolg08/03/2020 15:48:09
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11714 forum posts
1309 photos

Another factor that has barely been touched on, although noted, is how is the model powered.

When the model is electric, the vibration that damages a lot of IC servos, and sometimes electronics is rarely if ever present.

When I see those big 50cc powered models, with ultra light structures, where you see at least two models on every cycle. You really need a servo that can cope with the environment.

On those ultra fast gliders etc, I sometimes wonder if it is a control system failure, be it flutter, induced by a number of factors rather than the servo itself.

In my case cheap servos do all I need.

Andy4808/03/2020 16:02:43
1497 forum posts
8 photos

I try and use the same servos in each model. I standardised on Emax 11g ones, and so far they have been superb, and no failures. Most of my models fall into the 2-4kg sports model category and are electric, a good point as noted by Erflog. The weight saving is really significant. 4 standard servos at 44g = 176g. 4 11g servos = 44g.

A few basic rules:

1. I always buy metal geared servos.

2. Always use individual servos for each aileron.

3. I use straight pushrods wherever possible, and avoid snakes to keep friction low.I ten to use carbon fibre tubes with 2mm wire glued in each end.

4. Avoid the Chinese fakes. Even on £4 Emax servos, they are everywhere. Now I only get them from a reputable dealer.

Erfolg08/03/2020 16:52:07
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11714 forum posts
1309 photos

In my experience, perhaps that should be usage, the very cheap 9g servos I have used in the past, have never failed in use.

Where they are weak is to shock loads. Those tiny gear teeth do not like shocks. For example, walking into a door, crashing my way out of the house, in other instances random loading of one model on top of another.

Like many other people I am slowly moving to 9g types with metal gears. Unlike others, i am happy using Futaba std servos, the S128 and similar models.

I have had one partial failure (that I am aware of) and that was the loss of a tooth in a relatively expensive servo, that until recently, would be put forward as the Bees Knees. As it was around the neutral position, it provided extremely poor centering. It was only when on the ground the problem was identified. Even in This case, I suspect it was non flying abuse that was the cause of the issue.

Tim Ballinger08/03/2020 17:18:51
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778 forum posts
283 photos

Interesting you mention Emax servos Andy, I was looking at those on one web Site ( one I consider reputable) and see they have replaced the mini (17g) Analogue Emax with one of their own branded Mini digitals .

Not sure whether that implies equality or superiority but thanks for the Emax endorsement.

Tim

cymaz08/03/2020 17:20:05
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9197 forum posts
1186 photos

Hitec 645mg are my go to servos for a petrol powered plane. Also 625mg

Tim Ballinger08/03/2020 17:37:30
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778 forum posts
283 photos

Yes HiTec were my go to servos but beginning to wonder if I am just paying for the name. Perhaps it’s because I just fly electric now and as has been mentioned the vibration environment is so much more benign that failures are rare.

I also take Erfolg’s point about hangar damage but I have to be honest and even though I know you shouldn’t I will often push back a control surface following a knock rather than wait for power up to recenter the servo. Still not had any problems though........

 

Tim

Edited By Tim Ballinger on 08/03/2020 17:38:46

Frank Skilbeck08/03/2020 18:05:17
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4685 forum posts
101 photos

Just to add another one, does using a gyro stabiliser shorten servo life? (as the servo is working more).

Recently had an elevator servo fail on an electric model with stabilised receiver, been in use for well over 12 months, on 3rd flight of the day model took off and no response from the elevator, Servo wasn't a named brand one, can't remember what it was.

Denis Watkins08/03/2020 18:12:57
4335 forum posts
104 photos
Posted by Frank Skilbeck on 08/03/2020 18:05:17:

Just to add another one, does using a gyro stabiliser shorten servo life? (as the servo is working more).

Recently had an elevator servo fail on an electric model with stabilised receiver, been in use for well over 12 months, on 3rd flight of the day model took off and no response from the elevator, Servo wasn't a named brand one, can't remember what it was.

The 3 servos on the 3 axis are virtually working all the time Frank, as well as the flight battery

It is a small penalty, but you can cut the in flight consumption back by reducing the Gain to a minimum.

As a guide, the Gain can be so low that surface movement is barely visible

Yet the model copes in high wind

Martin McIntosh08/03/2020 18:31:00
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3332 forum posts
1178 photos

+++ for Corona DMG ones. Very powerful and reliable and have the look of quality, with a large range available.

On larger stuff there is little to choose from standard sized Savox, metal or plastic, and Hitech 5485 carbonite geared ones. Metal gears will wear and cause slop eventually so I believe that most F3A fliers stick with suitable plastic ones.

Never had a problem with any of the above (yet) and due to SMT technology there is very little to vibrate apart any more. Some of the mini ones I use on i/c models do not even have rubber grommets.

Peter Miller08/03/2020 18:34:12
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10966 forum posts
1272 photos
10 articles

I have been using 9 gram metal geared servos for quite a while now.Mainly Turnigy but one or two others. Not had any problems.

I picked up two 9 gram digital metal geared servos from Airtek recently which will be going in my next model.Just over a fiver each..

<y Li'lCub has six metalgeared 9 gram seros in it.

For ic models these days I use HITEC 311 servos.

Andy4808/03/2020 18:57:04
1497 forum posts
8 photos
Posted by Tim Ballinger on 08/03/2020 17:18:51:

Interesting you mention Emax servos Andy, I was looking at those on one web Site ( one I consider reputable) and see they have replaced the mini (17g) Analogue Emax with one of their own branded Mini digitals .

Not sure whether that implies equality or superiority but thanks for the Emax endorsement.

Tim

Yes I noticed that on the same website, as I was looking for slightly larger 17g ones, only because that size fits an ARTF I was thinking of getting. That size Emax have never been that common.

One thing I do like about the 11g Emax ES08MD/ES08MA series is the way the corner where the lead goes in is angled, so the servo can be slotted into a tight fitting servo box.

Don Fry08/03/2020 19:20:16
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4557 forum posts
54 photos

Plastic gears, vs metal. A proposition.

You have just stripped the gears from the plastic servo. How you did it is your affair. Change servo.

You have just stressed the gears from a metal servo. Are you actually claiming the rest of the gear train is stress resistant? Your airframe.

Tim Ballinger09/03/2020 10:24:17
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778 forum posts
283 photos

Don,

An interesting observation. If such a phenomenon exists I guess the nature of the beast is that any evidence for such failures would be difficult to come by. If a subsequent failure in the drive train did occur it would it not be the same as a plastic gear failure anyway so perhaps no greater a risk ?

So from the replies I have had I think I see support for the 9- 17 g class of servos for electric flight with no failure trends noted. I see the digital versions in this class producing higher torques (3-3.5 kg.cm) than previous at wider voltage ranges (4.8 - 6) being typical.

Corona and Emax servos have been called out as good as of course as Hitec.

Best value in the class I am looking at is another question but there has been a suggestion that some folks are having no problems with the cheaper offerings on the market.

Following one link to Airtek ( a shop I have not really visited before) I have also started looking quite favourably at K-Power servos.

Thanks for all the input I shall definitely be going with sub £10 mini ( 9-17g) digital ; just not sure what make yet.

Tim

extra slim09/03/2020 10:34:54
483 forum posts
48 photos

would be a good topic for a survey Mods.. this more than any other market has changed a lot recently, so would be interesting to see what people use and for what and how they rate them..

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