I know this isn't the best forum for this question, but I've always got good advise here. And I'm still a beginner, maybe a little ambitious, but I want to learn how to fly 3-D.

I've read a lot on RC Universe about using different servo's on different control surfaces on 3-D type planes. What are the benefits of that? And with a Fataba 7C, which servo's would be recommended for the Ailerons, Elevator and Rudder.

What servo's to use depends a lot on what model plane your flying. The bigger the plane the more powerful the servo's will need to be. 3D planes that have large control surfaces with lots of throw will need powerful servo's. Something like a 46 size UCD 3D needs about 90 inch ounces of torque per surface.
Using different servos may be due to people using what they have lying around or because they don't want to waste money on an expensive servo that is 3 time more powerfull than needed. Usually rudder servos are the most powerfull.

The best way to determine what size servo (oz of torque ) you need is to use this calculator.

http://www.csd.net/~cgadd/eflight/calcs_servo.htm

Just plug in the numbers and you will know what you need.

Some of your smaller profile and 4 size 3D machines mixed with proper thrust to weight ratios and propped correctly also makes a big difference do not require tons more torque than your trainner. They do require more but no where near 70 to 80 oz. Carefully select your first 3D bird and choose it on ease or repairs and initial build. They do need to be rebuilt especially if you are a novice 3D piliot. Servos shouldnt get too pricey in the 15 to 20 $$ range for each even some of the duel ball bearing standards will probably be fine for a 40 size 3D plane. I suggest a profile plane for ease of all of the above reasons. However to each his own. I have a Morris knife profile been flown for 2 seasons with a YS .63 on it. And I run all standard servos with 50 and 60 degree throws never a problem. Bottom line you can get all types of opionions in here as to what the best servo is but, no one person can tell you. Do tons of research read all posts and explore the ins and outs on the servos websites. I have a Funtana 90 10 lb 3D plane with a YS 1.40 in it and I use the Hitec 5475 Digital Karbonites $ 35.00 a piece 76 oz of torque @ 6v and its pleanty. But it took me a lot to get to where I was comfotable buying them. Theres just soooo much info on all the available servos and all of there pros and cons.

With servos, there are 3 things to consider.

Torque - you need enough force for the servo to move the control surface through the desired throw, and keep the surface there. Keeping in mind that standard servos are prone to "blow back" because they only develop their rated torque when moving. They don't develop the same torque when trying to hold a position. (if you have a servo you don't mind messing with, try bolting on a long horn, then try fighting it with your fingers. You'll find it's not hard to move the servo a small amount from any position, but the farther you move it, the harder the servo fights back). Max torque occurs when the servo is farthest from where it wants to be. Digital servos fix this problem. They produce nearly max (or max) torque even for small deflections. (which is why they suck battery power like crazy, they are always working "full power"

Speed - You can get servos that respond faster to your contorl imputs. You might not think this is a big deal, but depending on the plane, you can actually feel when the controls move faster. This is espeically helpful in some acrobatics, including 3D

Precision/resolution - This is really several things that I'm lumping together to keep an already long post from getting truely epic. Basically, some servos center more accurately than others, some go to the same end point more consistantly than others, and some have smaller "dead bands" than others. Deadband is the range of stick movment that results in no servo movement in response. In theory you want 0, but in reality, you need a little deadband to keep the servo from constantly hunting or jittering. (at least in standard servos. I don't know how deadband affect digital servos, I think it's the same, but I don't know for sure).

Anyway, you can pay more for servos and get better torque, better speed, and/or better resolution. Which might or might not make some acrobatics easier (or possible).

Picking servos is something of an art and heavily based on personal preferance though.

Sorry to pick your post apart but as far as your torque explanation goes. Torque has nothing to do with holding power in a servo they are considered 2 separate components. Torque rating in a servo is the power behind the swing all anolog servos dont reach full torque until they are 20% into the throw of the swing. Digital servos have it from the get go there percision is from their pulse 5 times faster than an anolog servo 60 vs 300. Now as for holding power that comes into play as the gear set composote. Karbonite, plastic or MG and the gear train layout all have to do with how well the servo will hold at any deflection. As far as deadband goes there is 0 in digitals that is why they always make a humming noise they are constantly maintaing a 0 dead band. The hum is normal so is more usage out of your battery. If you choose to go digital consider a 6V battery first and nothing lower than 1500 MAH. Anolog servos do give the most sloppy deadband and along with chatter MG servos have their fair share too, however its a compromise when you need more than 80 oz of torque. There is no karbonite servo out yet with a higher torque rating than 76oz I think.

Joeb,

Actually, you didn't contridict anything I said about servo torque. Torque is torque. Measured in in/oz. Holding power is how much Torque a servo can develop when stationary, or for small deflections. Which is what I was talking about when I mentioned that non-digital servos don't develop much torque for small deflections, and suffer from blowback. We're saying the same thing. I just didn't use the buzzword "holding power".

The pulse rate of a digital servo is higher. But for other readers, the pulse rate is between the servo board and the servo motor, not between the servo and the RX. Basically, the board in a digital servo updates the motor's location more often, which is part of the reason the motor develops full torque at small deflections. More importantly, a digital servo's control board delivers a higher voltage to the motor for a shorter burst of time, while an analog servo board delivers a lower voltage for a longer time for small movements. Lower voltage means less torque. The only time you see max voltage to the motor of a non-digital servo is when the board wants to move the servo far enough that max sero speed is reached. You said 20% of movement, and I'll buy that as about right. (never tried to measure it). Taking apart a servo and playing with the pot and motor with a voltmeter really tells you a lot about what is going on, btw.

However, I totally disagree about gear train makup. Torque delivered has zippo to do with gear train material. That is, up to the point where the gears fail. But short of stripping gears, nylon, metal, karnonite, unobtainium, whatever, gears are gears and follow the same laws of physics no matter what they are made of. Now, you can get more speed and less torque or more torque and less speed from the same servo motor by changing the gear ratios. And, in fact, many servo makers do exactly that. But if you keep the same gear ratio, the torque and speed won't change with material at all.

If you don't belive me, get a servo like an HS-81 (or any servo that comes in nylon and metal flavors). hang a weight from it and see what the max developed torque is. Now replace the gears on the same servo with metal and do the same experiment. You'll get the same result. (plus or minus friction from the gear train, but that's going to be almost unmeasureable).

Gear train also does not affect deadband. Gear train DOES affect backlash, which in some ways acts like deadband, but you really shouldn't confuse deadband with gear backlash. It is true that metal gears usally have more backlash, and when they wear, they develop even more. Nylon is great for wear and backlash reduction, but the gears are weaker, and sometimes can be stripped. Karbonite is an attempt to get metal-like strip restance and strength with nylon backlash and wear.

There's also no reason to go to a 6v battery with digital servos. Remember, a 6v battery will drain FASTER than a 4.8v pack at the same capacity. So, if you have a 1500 4.8v, you will get MORE flight time than with a 1500 6v pack. You do get more speed and torque (and smaller deadband on non-digital servos) when you go to 6v though, so people who are looking for every bit they can get from their gear find it worthwhile to use 6v. But if you aren't on the edge of your servo's abilities, there's no compelling reason to use 6v.

(The other reason to use 6v is that if your pack drops a cell, you still have enough voltage to land, or at least direct the crash to a safe location. But cells usually don't fail in the air, and if you check your packs carefully, you can usually detect a cell going bad long before you get in to trouble. But battery safety is beyond the scope of the thread)

I Hope you dotn think I was bashing your post because I assumed you didnt know what you were talking about. Quite the contrary I was definatly misunderstanding you when you talked about torque and holding power in the same sentance. I do not believe that torque and holding power in a servo are the same. Holdng power has nothing to do with the torque out put of the servo. But it does have to do with the gear make up MG vs plastic. You stated that I said "However, I totally disagree about gear train makup. Torque delivered has zippo to do with gear train material." I said noting of that, I do not think torque has anything to do with gear train make up. However I do think it hasa somehting to do with holding power which I stated and still believe that torque and holding power in servos are totally different. In short I think we are both saying the same thing here an just misinturpiting one another. I also never stated the gear train does or doesnt affect back lash all I stated was the benifits of a cheaper digital servo vs an anolog. IMO if you dare not going to use std 3004 or 3003 and need to upgrade these are the best bang for your buck. I agree with going to a 6v battery however. While there may not be negative recourse for using one to the other there is prefrence and IMO 6V far outweighs a 4.8 if they drain the same you are only gainning extra speed and torque which is sometimes required. If I was to need a 75 oz servo and I had 2 choices ditch the 4.8 pack and get e 6v or swap out all my current servos to get ones with that rating at 4.8 I am buying a 6v battery. Clearly we have 2 opionins based on the exact same facts. I didnt intend to make this a debate but to more clarify so there was no confusion.

Kirk knows his stuff alright, Sounds like you do too Joeb!

But as for the question, as was already mentioned, the servo used is more related to the plane AND the type of flying as opposed to just the 3-D Flying.

There are several 3-D planes that will fly well on standard servos (Modeltech's Magic Extra comes to mind)

Don't sweat it, I wasn't bashing you and I didn't think you were bashing me. It's fine to disagree a bit, or correct something. I don't think I'm perfect, that's for sure. And while I try to be clear, I know I'm not always. Nature of these boards.

I didn't think you said anything about gear material and backlash. I was just going in to more details about deadband vs backlash as I thought you were mixing them. I could have mis-read what you wrote, however. Still, the info could be useful for anyone else reading. Anyway, the differnet backlash of the different gear materials was just something that came out "along the way", I didn't intend it as actually responding directly to anything you said.

As for cheaper digital vs non-digital, I agree, for many applications, digitals are worth the money. And there are few applications where digital would be a bad thing. Eventually, I think most all servos will be "digital" as the price comes down on them. It's just a better way to do things.

Your thoughts on 6v vs 4.8v are fine of course. As you say, it's really a matter of preferance. I've never needed to go to 6v, though I did try it out a little, and I didn't notice any difference in the plane I tried it on, so I went back to 4.8v. Obviously, in that case, the limiting issue wasn't the servo output, but other aspects of the plane. (note that I didn't say other folks wouldn't notice the differnece, or that no one should bother. I'm quite sure that in some applications, the boost on the servo would be more than worth while).

As for holding power, I disagree though.

I don't think it has anything to do with gear material. Can you explain how just changing out the gears in a servo will result in more holding power? It doesn't match my experience with servos that I've converted from nylon to metal gears (after stripping them out).

I mean, holding power is the amount of torque a servo can produce to try to resist movement from a given location, correct? It's just torque. And it's only become something talked about with the recent introduction of digital servos that produce full torque even for small deflections, which is in contrast to old style servos that don't produce full torque until the deflection gets to be beyond a certain point.

(in case I'm not being clear, what I mean by "deflection" is the differnece between where the servo is now, and where the servo wants to be, ie the commanded location. )

Now, if you're using "holding power" as a catch-all term to mean a combination of inital torque (ie torque for a small deflection), deadband, backlash and resolution to talk about how well a servo as a whole holds an exact position, then I don't disagree with gears mattering. But that's not what I think "holding power" means.

(another side note, servos are only part of the deal of a control system, of course. Things like pushrod flex, slop in linkages (such as a clevis pin being a hair smaller than the hole it's in), and so on, can make a bigger difference than any servo. I know joeb knows this, I'm just pointing it out for the origional poster and anyone else reading.

In a nut shell heres my inturpretation of torqe vs holding power. Maybe I am using the wong terminology from what i have come to learn is that torque is used to get the servo to deflect to the point where you want it, and holding power is the servos ability through gear train and composite make up to hoold it at that location until the operator releases the stick. Of course I am not alwas correct and if this is not true then I am all ears.

torque is angular force. It requires force to move the servo control horn. The more torque the servo has, the more force it can move that surface with. Larger surfaces require more force to move. If nothing were fighting back against the servo, then there would be no force required to hold the surface deflected--no torque. However, we know that as long as a surface is deflected into an airstream, there is force fighting back. The only force available to hold the surface deflected is that from the servo--the angular force created by the motor inside the servo--torque.
Therefore, torque is torque--whether it's the force required to move the surface, or the force required to balance the opposing forces when the surface is deflected.

Ok guys, this thread is about which servos he should use, let's keep it on topic. Thanks

Re: "The hum is normal so is more usage out of your battery. If you choose to go digital consider a 6V battery first and nothing lower than 1500 MAH. "< good info, I wasn't aware of that!! [8D]

But Minn, knowing how a servo works and the difference between digital and non-digital is important to picking servos. Otherwise, you might be surprised when a 45in/oz digial servo allows you to hold a better knife edge than a 60in/oz standard servo. Unless you understand the drop off in torque with standard servos, you could end up with servos that just aren't up to the job for acrobatics. (making the example up, btw. Don't quote me as saying a 45in/oz digital is equal to a 60in/oz conventional in holding ability).

Btw, in some 3D such as hovering, you don't tend to hold the controls hard over against the airstream much. So holding power isn't as critical. Servo speed matters more in a hover so you can make the very fast corrections needed. On the other hand, a knife edge loop is going to require much more holding power, but the servo speed matters a lot less.

belfish, I would get a profile for learning 3D. Standard servos work fine in these planes. Hitec 425's are very popular with 40 size profiles. They aren't the best but if you are just learning, you probably won't be able to tell the difference anyway. I think the best overall value for 40 size 3d is the hitec 635 servo. I have used them and I believe they offer more bang for the buck than any other servo with comparable specs out there.
You asked about what servo you should use for each control surface. The rudder should get the servo with the highest torque. The ailerons generally get the lowest. This is my newest plane. It is a kit built omp 47" yak. All servos are hitec 425's except for throttle which is a hitec hs 81.

I live in Marietta and fly at the Cobb County Radio Modelers Club. You are about 1/2hr away. Feel free to come down sometime and fly with us if you like.

For a good amount of .46 and some larger 3D planes you only need standerd servoes, and maybe a high torque for the rudder

Thanks for all the input. It was spirited, but I learned a lot of technical stuff. I am starting out by assembling a SPAD I purchased from a shop out of Villi Rica, GA. I can learn without costing me a lot of money, crashes well with minimal damage. Should keep me busy for a few months.

I also purchased a Hangar 9 Twist from the show in Perry, GA a few weeks ago. This I won't assemble until I feel I can fly it without crashing it right from the start.

I think the SPAD will have standard Futaba 3004's, maybe something else for the rudder. What's recommended? It will have a OS .46 powering it.

The Twist I am completely open for suggestions, but remember I am using a Fataba 7C radio.


Thanks
bbell

This is your first airplane???

Do you have an instructor?

No, not the first. Started with a Hangar 9 Alpha 60 trainer. I am still working with my instructor, but hope to soon cut the umbilical cord. And I know I may be a little ambitious. I plan to stay with the trainer for a while before flying the SPAD.

Cool... Spads Rock.... fun to bang around with!