Servos

[001]

In a similar vein, take the example of the rev. counter (tachometer) on your car.

On the face of the instrument it says rpm x 100.

It could be said that it should be RPM divided by 100 as the information presented is such!

Depends on how you look at it.

 

[Peter Miller]

I really hate to interrupt all this highly technical and mathematical argument with anything that might actually be useful to readers of the original chart but I will.

 

You can now get micro servos, i.e. 9 and 14  gram servos with metal gears. They also have over 1 Kg per centimeter torque.

 

This overcomes the problem of weak gear trains.

[Hamish]

Delighted Peter, that someone of your eminence has brought this posting back to earth.  Reading the initial heading I  thought this was just what I  need as it should of provided me with an indication as to what size to use and where.  I found the chart only defines what the various size are but not where and what  to use.  I appreciate that different models will require different sizes and this was what I was after.

 

Thankfully David Ashby provided a link to previous postings that are of great assistance

[Myron Beaumont]

What we really need to know now is the forces on ailerons/elevators /rudder in order to choose the torque required at the speed through the air of common types of models that we fly .I myself use & have always used standard servos for everything except aileron ones where there is one in each wing (mini) & the throttle. Only 'cos everybody else does ! & they work! That is to say on IC models of up to 60 " span 'ish

Peter -Tell me what servos you're talking about ? I'm never really up to date !

[Tim Mackey]

Posted by Peter Miller on 27/02/2010 08:32:11:

I really hate to interrupt all this highly technical and mathematical argument with anything that might actually be useful to readers of the original chart but I will.

 

You can now get micro servos, i.e. 9 and 14  gram servos with metal gears. They also have over 1 Kg per centimeter torque.

 

This overcomes the problem of weak gear trains.

 

Yes, but I still dont think the overall "ruggedness" of a 9 gram servo - despite its gear material - will be as good as a standard size servo. This assumes various things of course, such as quality of fixings, case material, mounting lugs, and output arms etc.

There are some situations where a mini or micro just wouldnt cut it in a large model such as a fast slope soarer which is landed on rocky or other tough terrain. Some of the mini and micro servos I have encountered literally fell apart as they were being handled - some of them even just use the sticky name label to hold the case together !!

Of course, price plays a part too - with everyone now wanting a servo for the priceof a cup of tea.

I await the counter attack

Edited By Timbo - Administrator on 27/02/2010 09:23:04

Edited By Timbo - Administrator on 27/02/2010 11:14:27

[Peter Miller]

Timbo. I couldn't agree more.

 

I used Supertec Micro servos on a Sig Clipped wing CUb. They worked OK but when I knocked one it stripped a gear. That ruined an evenings flying..

 

I now use the 14 Gram MG servos. One per aileron, one per flap on my Luciole. My Slingsby T31M has one per aileron and one for the rudder and one for the elevators. This model is slow and gentle. I also use the same set up on my Piper Pawnee powered by a .32. That isn't slow or docile in comparison. No problems there.

 

My current design is a 48" span Wittman Tailwind for .30 FS power. I am using the 9 gram Metal geared servoes, again. one per aileron and one per flap.

 

I buy these from Storm-Trade on Ebay for those who want them.

 

With regard to the power, they are well over 1 Kg per centimeter each and so have as much or more power than a single standard servo.

 

They are screwed together and they work for me.

 

For years I used Supertec Mini and Mini Ls. these are a bit bigger and actually are claimed to have more torque than the standard servo.

 

I still use them in some models.

[Barrie Dav 2]

Timbo was your 'slop' soarer jerry built?

[Myron Beaumont]

Peter

Thanks for the info -I'll stick to Futaba 3001's & the hitecs for ailerons . Cost never came into my equation when it comes to peace of mind.

[A.A. Barry]

Am to believe, from other posts, in this thread, that 14g mg servos,are as good as a 3001???

I need two throttle and two flap servos for my  DC3 84", so on the above postings,  this would these be acceptable (14g), ????????????

A.A.Barry  

[Peter Miller]

I would say that they would be great as throttle servos. I won't commit my self as to yopur flap servos. that is a big model.

 

Myron. The 14 gram servos are not cheap by todays standards, around £9 each depending on how may you buy, the 9 grams ones cast nearlty £30 for four.

[Tim Mackey]

Posted by Barrie Dav 2 on 27/02/2010 09:41:12:

Timbo was your 'slop' soarer jerry built?

  LOL ...however thanks to the power of unlimited editing privileges - I am sure I don't know what you mean Barrie

[A.A. Barry]

Thanks, Peter, I was in doubt, Hitec HS-82mg should fit the "bill"

 then??

B

Edited By A.A. Barry on 27/02/2010 11:31:54

[Barrie Dav 2]

Well Timbo. It was just an obscure little joke with no offense intended.. 

 

My old granny lived in (very) rural Wales in the 1940's with no inside toilet so she had to use a 'jerry' (chamber pot) to slop out  when she got up in the morning.  And I was relating to your typo, which we all make from time to time.  Which I now see corrected.

Hence was the crashing slop soarer jerry built. i.e. badly made...

[Tim Mackey]

I know it was Barrie  - thats why there is a in there mate!

Absolutely no offence taken...why would you think there was .

[Phil 9]

Some complex discussion here and it has not helped me understand servo choice any better.

I need some standard size servos. But there is not much standard about standard servos except the case size (or is that the point)

I have bought cheep servos in the past (with mixed results). there is a range of servos from different manufactures ( about the same specs) at different prices but is price a good guide to quality

also now the lower end digital servos are about the same price as higher end analogue servos. So what do I chose and how?

[Steve Hargreaves - Moderator]

Servos.....a faciniating subject!! I think we suffer from too much choice....in t' olden days you had a standard servo (about 3Kg) & that was that but now............literally dozens to choose from....same size but higher torque....smaller but the same torque!!!

 

A question I have often asked myself is when does a 3Kg "standard" servo no longer have the oomph to drive the control surface. Obviously a 9g jobbie isn't going to be much good powering the rudder of yer average 50cc aerobat but what about a 60 sized aerobat....3Kg Ok?.....how about a 90 size aerobat...should we go up to 5-6Kg now?

 

As I say....a facinating subject...

[Richard V-D]

Fascinating!  It's mind boggling.  As a newbie, am I right in thinking that servo's from different makers have the same type plug and are therefore interchangeable.

 

Or to put it another way, which servo to use in a .46 trainer with Spektrum radio?  I thinking, standard, not digital, but maker?

 

Help!

Edited By Richard V-D on 14/09/2010 10:35:46

[Tim Mackey]

Different brands use different plugs, and also different colour coded wiring ( dont ya just love standardisation )

However, they are all pretty much interchangeable, although futaba plugs will need the little "tab" slicing off to get them into non futaba receiver sockets.

[Tim Mackey]

Incidentally, most .46 sized trainers will use "standard" servos - and again, any make is fine.

The good ol futaba S148 for example, but there LOADS to choose from these days, and with an IC engined model, its generally best to avoid the mini /micro servos as they are not great at handling the vibration and gunge from an IC engine.

[Lee Smalley]

ignoring the kg.cm/ cm'cm[cm debate what most starters to this hobby are interested in is what sort of servo suits what sort of airframe and what is the difference between std/mini/midi/micro/sub micro and all the others in between, for a newbie it must be totally baffeling and to confuse the issue (as well ment as it was) with the Kg.cm debate is not going to help what would be lovely for them is a simple look up chart with wingspan and airframe weight and flying style and indeed power system all cross referenced to a recommended range of torque output size and gear types, it would be tough to do (so many variables) but useful 

[TheFlyingCrust]

Blimey. It's been a long while anyone posted here!

For a keep-in-the-boot model I'm making an own/design e-glider and needed a couple of inexpensive servos, so bought a couple of TowerPro servo's from Giant Shark. An MG90D and 4 SG92R's, The former because of the ball races, it's for a closed loop rudder, and the latter because they look good value.

Now there are reports the MG90D isn't actually digital, if you look at the link there's no 'D' on the badge and also not on what I've got, but I'm not that bothered. (I wonder how I can tell?) What's interesting its direction of rotation is opposite to the SG92R's and to other TP servo's I've got.

This isn't an issue for me but I mention it as a point of interest. It might be useful in some applications.

Ian