Looking for info related to calculations, flying, etc. - RC Groups
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Jan 14, 2013, 06:56 PM
Registered User

Looking for info related to calculations, flying, etc.

While I am still beginning to learn how to fly, I am also looking to expand my knowledge of the hobby.

I was looking at a couple of build threads here, and people were trying to determine what servo's to use (for torque) based on plane size, speed, etc. as well as other items such as size of power source, size of batteries/ESC.....

I was running some searches, trying to find info related to all of this.
I found a site that explains the batteries, ESC, what servos are and the different kinds..

I am almost looking for a beginners guide to building or assembling. Does that make sense?
Any good books, pdf's, or just over sites that have this info that I can look over for the time being?
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Jan 15, 2013, 08:16 AM
An itch?. Scratch build.
eflightray's Avatar
This Beginner Training forum has some very useful 'Sticky' threads at the top. Likewise some of the other forums may have them. They are accumulations of knowledge and advice, well looking for and worth reading.

There are so many forums here on RCGroups that it is also worth just going to the home page, (click on the transmitter icon/RCGroups link at the top of any page), and scroll down to see all the different types of model possibilities. Those different type of model may require different considerations, (calculations etc), to ensure they are successful.

Down the list, (before you reach the Boats, is the Balsa Builders forum, very good if building a kit etc, the Builders Workshop, where general 'how do I' questions are often solved. Again for the foam modeler, there is a Foam Kits, and Foam Builders, forum.
There is also a Modeling Science forum for the very technically minded.

In fact there are so many forums it can get a bit confusing to decide where to post. The Advanced Search is quite good, as it has other options to help find specific things, it even lets you choose which forum or group of forums to search in.

I would say beware of trying to find out about too many things, and forget about the best part, flying a model plane.
It is often easier to look at what other have used for the same or similar model, than to 'reinvent the wheel' each time. It all helps build a knowledge base, of what you may need to know to help, rather than try to learn everything and not really achieve anything.
Jan 15, 2013, 09:20 AM
Proud member of LISF and ESL
This is copied from a thread I have running on another forum called, " Let's Talk About Servos".

When I was a new pilot I was confused about servos, how they were used, how they were mounted and how to pick them. So let's start a discussion about servos for all the new pilots.

Let's talk about types, sizes, how to pick them, etc., whatever you like.

Here are some general comments to get things started.

Servos are rated by:

Size - Length, width and depth
Strength - Measured in inch/ounces of torque
Speed - Measured in degrees per second
Weight - Ounces or grams (28 grams to the ounce)

For illustrations I will use Hitec's servo line but my comments apply to other brands as well.

Hitec web site -


Some servos have no bearings. The plastic case essentially holds the shaft and supports it against pressure in use. The Hitec HS-55, HS-81 and HS-82MG servos would be good examples of servos with no bearings. They are very inexpensive and work quite well when new, but over time they wear and tend to lose their centering ability. However for light duty sport use they are fine.

I have many planes with these and similar servos of other brands. However today I generally buy servos that have some kind of bearings. These hold center better over time and move more smoothly over time.

For example a Hitec HS-85 BB is about the same size but a little more expensive than a Hitec HS-81 or 82. If I were putting a new sport plane/glider together I would chose an HS-85 over an 81/82 because the HS-85 has bearings to support the shaft.

Another example would be the HS-55 which does not have bearings. The Hitec HS-45 and HS-65 have bearings and can be used in similar situations. Partially because of the bearings they should center better and run smoother over a longer useful life.

Analog vs. Digital Servos

There are standard or analog servos and and there are digital servos. I will use Hitec brand again as examples but I also use JR, Airtroncis, Spektrum, Futaba and other brands.

Analog servos are typically your lower priced servos. They work well in most sport applications.

Digitals would be my preferred choice for any form of a competition plane or high speed planes.

For me the main benefit of digitals is more precise centering. They can also tend to hold position better under force, but they will pull a lot of power to do it.

If you are flying at 150 mph you don't want those control surfaces being blown back because the servo can't hold position. And in any kind of competition you want those servos to go to the correct center or offset EVERY TIME and hold there solidly. Small variations can be a real issue in competition.

Some brands, like Hitec, have basically the same servo in analog and digital. For example:

Hitec HS-85MG - Analog

Hitec HS-5085MG - Digital

They are the same size, same spline, same ball bearings, same gears, but have different control boards and maybe a different motor. You can swap one for the other in your plane and they will fit.

In my competition planes is it all digital servos with bearings. I use Hitec, JR and Airtronics digitals. I have to have solid centering in these ships.

Spare Servos

If you standardize your servos, trying to use the same ones over and over, you can minimize the number of different spares you will need. When you are first starting out, this may not be a concern, but as the fleet expands somewhere along the line you are going to break a servo gear or have a servo fail. How you deal with this depends on how prepared you are.

I always keep spare servos in my field box. If I am going to an away contest I will have the servos that match the digitals in the planes I bring with me. But some of my servos cost $50 or more, so keeping lots of spares spares in the box, hopeful that I will never need them, can be expensive. I have found that a Hitec HS-85 can handle the duties of most of my digital servos, in a pinch, just to get me through the day. When I can I will replace that with a digital servo that matches the one that broke.

I have some of the Hitec HS 81 and HS-55s in my field box as emergency spares. They get me through the day at the home field and work well enough and can cover a wide range of applications. Best of all they are low cost so they do not represent a big investment to just toss in the tool box for unexpected field repairs.

Just this past weekend I had a servo strip in my Radian. I pulled out an HS-81 and in 20 minutes I was back in the air. They will keep me flying if I need one at the field. And if a friend is in need I can offer them a servo without breaking their bank or mine.

I added a servo calculator. I did not write this but the results look reasonable. This may be helpful when fitting out a new plane where you don't have guide lines for servos.

So, what do you know about servos that you would like to share?

What questions do you have about servos?

Let the discussion begin!
Last edited by aeajr; Jan 15, 2013 at 09:35 AM.
Jan 15, 2013, 09:39 AM
Proud member of LISF and ESL
As for building help. What kind of building do you have in mind? Foam, wood, composite?
Jan 16, 2013, 09:06 AM
Registered User
I figured I would start with foam or whatever is "easier".
I figured this would be a fun project, and would help me get some good experience with how everything works from electronics to aero.
Jan 16, 2013, 02:06 PM
Proud member of LISF and ESL
If you have no real building experience I would suggest you start with a kit. It will teach you a lot AND give you a very high probability of success.

Great wood, wood/foam kits


some nice looking foam kits

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