RC India

Guys,

What is the basis of selecting a servo? We do see a lot of different variety in terms of weight and size of the servo. So how does one choose?

Pankaj

Strange that nobody has responded to this  so far ....  :o

The following factors play into servo selection :

1. Size (sub-micro, micro, mini, standard, etc)

2. Torque (this is probably the most important factor.... after size, which you do not usually have much choice about, especially if it it is a kit/arf).

3. Digital versus analog

4. Type of gear (nylon, karbonite, metal)

5. Operating voltage range

6. Type of motor inside etc (coreless, brushless etc).

7. Price/brand !

So to start with, look at the size you want, and the torque you are looking for.  After that, pick from the choices available in terms of price and other features.

Has anyone ever opened up a servo before ? Any pic or cross sectional view would really help as i was just curious to see how the inside of a servo looks like.. :D ;D

cheers

atul g.

Hope u find this useful, jus follow the english subtitles.....
http://www.youtube.com/watch?v=-XSXfqd1N58
Edwin

i have opened many many servos before atul bhaiya wait i will open up one of the dys one and post a pic as soon as possible

i have changed couple of wires and done the 360 degree rotation mod before too


subbu

mr.edwin and subbu,

thanks guys... tat was the fastest information i ever got..and oh yeah tat video was super kool , thanks for digging it out mr.edwin.

cheers guys..

take it easy...

atul g.

If you haven't opened up a servo and changed the gears, you are not flying enough (and crashing enough) ;D  :P   8-) 

Or you are stinking rich (always using metal gear servos, those tend to survive crashes much better than others)  :D

oops sorry in the above post i meant changed a couple of gears not wires sorry

anyway anwar bhaiya lets make a thread on how servos work i have taken some pics of an open servo and an open servo working



subbu

hehe anwar..yea am not crashing and flying enough..dont get much time  :'( except on sundays..

Stinking rich and me ? hello u are the one who has software companies.... :P

All the best..

atul g.

You want a software company ?  All it takes is an entry level CA (chartered accountant), and a few thousand rupees.  If you do not feel convincing enough because you are alone, ask someone who were in your class to join you  :P

Who knows, in twenty years, you have a billion dollars in sales ("Infosys"; faster for some others) !!!

 ;D you want to start a company with me in pune city..  ;D  ;D after the swine flu gets over, of course.. 8-)

hi anwar

how does one know what torque requirements he needs  ??? any scientific way of selection/calculation  :)

sahil

anwar  8-)

Hmm.  I guess that would take like wind-tunnel (more like wind-shear) tests etc to do it right ?  :P  But you can always over-engineer.

Scientific ??!?!  Next question, please....   8-)

BTW, there are all sorts of torque calculators on the web, which take into consideration lots of factors.  

http://www.google.co.in/search?hl=en&q=calculate+required+servo+torque

Some of the variables are pretty "unique to you" kind of things, like your flying style.  For example, someone doing 3D on a heli needs much more torque than someone who does just regular flights or even sport flying.

The "weight of the model" is something that is a significant influence. But if you are asking for a formula, I am not sure if there is one that is universal.

nice scientific answer  ;)

bye

sahil

it will be one company to watch out for

anyway anwar bhaiya we would love to know about your company (i already doo) but a few words in which you describe your company and your work

other than posting the link of http://www.systalent.com/ (http://www.systalent.com/)

which i have gone through many times

subbu

Let us keep the unimportant personal stuff to PMs ;D

At the moment we have our hands full pushing Sai into a corner about the 2.4 stuff  8)

alright no prob ;D


and we can see its effects already as he converted to 2.4 (only one tx) but hey change come one by one let get on to the task  ;D ;D ;) ;)

 ;D ;D ;D

another question which i just though i would ask why is it that we always have the 2.4 G included in nearly every thread we post in  ;D ;D ;D ;D ;D ;D

So guys, can we have some rough thumb rule for the torque selection based on the weight of model, engine size (?? some indicator of the speed) and type of flying  - sedate or 3D?

While we can always settle for a higher torque model, but then it will not only add more weight but also burn a dent in the pocket.

Pankaj

Anwar's login anwar2.4G should be the way to go :D ;D {:)}

Look out for another 2.4 G Hack on a cheapy tx soon ;) ;D

Sai

Pankaj ,
It normally works like this :

Plane weight                          Servo                  torque
around 300 gms                      3.7 - 6 gms           1kg
upto  900 gms                         9 - 12 gms           1.5 kg
1 till 1.5 kgs                            16 -22 gms           2 - 2.3 gks
1.5  till 2.5 kgs                        36 - 42 or 55 gms   3 + kgs
3kgs and above                       similar to above range

Practically 36 gms and above are all variations of the standard servo  and weight is really not an issue here  so do it as it suits you as you are talking of a band of 20 gms weight per servo at best hence even if you have 7 servos on the plane  all at the 55 gms level  you would only be adding 140 gms to the set up. Hope you get what I mean.

The smaller ones are the ones where the weight to torque is a critical factor.

Sai

Guys,
Need to understand more on servos,
The sites are listing servos by way of Fatuba, JR connectors etc. So the question is that are the servos tied to a particular Tx /Rx combination?

Also what is a 'dead-zone'?

Pankaj

Pankaj,

The connectors on the servos have futaba connector or JR,Airtronics,Hitec,etc type connector.

Most cos had their own proprietary connectors. Now only futaba continues to use its own proprietary connector. The Futaba connector comes with a notch on the side.

Most of leading radio/servo manufacturers use common type of connectors now.

You can easily cut the extra notch out on the Futaba servos to make them look and work like JR.  Or use a file to shave it off.

True

Earlier they use to have different wiring also but that has all changed now. They use the same/common type of wiring.

A dead-zone helps reduce wear and power usage by the servo by not responding to input until the input has changed by some preset/minimum amount.  Otherwise, if the signal is slightly unstable, the servos will work themselves to death.

http://runryder.com/helicopter/t398911p1/

Pankaj

Why dont you have a look at the following URL:

http://www.pongo-air.com/servotorque.html. There is a free torque calculator based on wing chord, wing span, speed etc.

Happy flying

Saju

This is really kool.. thanks Saju.. it surely is helpful. But i need to know the airspeed of my plane... how do i do that ??? :)

Saurabh

Here is another site where the same fomulae are used but is online : http://www.csd.net/~cgadd/eflight/calcs_servo.htm

The air speed of the plane has to be approximated from the motor-prop-battery combination with other details of the plane. You can do that in Webocalc or drivecalc or motorcalc. All this is theoretical, but experiences have shown them to be manageable.

Happy Landings

Saju

Thanks Saju.. Useful info.