Troy Newman
Posts: 2429
Joined: 12/30/2001
From: Goodyear, AZ, USA
Status: offline
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I have been away from the Focus Sport a few days. Sorry about that. I’m going to be getting with it over the next few days. To be honest I have about double or triple the time in writing the build thread compared to doing the work. The model has gone together very well so far.
Now that the model is mostly assembled its time to discuss the servos, linkages, and optional things within the airframe. We need to get this settled so we can get parts ordered. After discussion of the parts and choices I will give you guys a list of parts to order from Central Hobbies. This will include some extra stuff like Hyde mount if you choose and also spinner sizes and some extra goodies to finish it up. Again I’m giving my advice on this stuff and will back up my choice with my opinion and why I feel the way I do about the choice. Your choices may vary depending on your needs and decisions. I’m going to try and give you some good choices that are less over all $$$ but will still perform well. Will it perform as good over time as the EXPERT setup…in some cases yes and in others no but we want to discuss why some the choices are being made.. End result it will perform well. There are good choices in cutting costs and there are not so good of choices.
The idea behind a pattern model is to get it trimmed out and have the model stay trimmed out as long as possible. Trimming an aerobatic model is a never ending process. Things are constantly changing and you need to keep on top of the model. Many of these choice in equipment will help the model perform the same on flight 10 as flight 100, as flight 500 and even flight 1000. This means that wear from vibration can be your enemy. The accuracy of your system and your flying really comes down to the linkages, and servos you choose. If you choose a bargain brand servo because it saves a couple bucks that’s fine just realize that servo may not last as long as the higher priced servo in the same environment. Will it do the task properly? In some cases yes it will, but it will change and degrade quicker over time. Another thing to realize is that just because the servo moves the surface doesn’t always mean its going to work the best for precision flying. On our pattern models torque of the servos is a concern but is minimal for the most part. If you follow the linkage setup that I will be doing once we make these choices on servo the mechanical advantage and symmetry of the linkage will benefit the servo. This means that you don’t really need the strong servo as we are not going to be moving control surfaces far. The control throws will be small deflections and the result is the servo will have a leg up on the controlling the surface. By using a longer control horn on the surface and a smaller servo arm we will give the servo the advantage. The point I’m trying to make is that everybody always looks at a servos torque numbers. Instead I look for the servos performance and how accurate the servo is under the continued use we are going to give this model. The goal is to set it and have it last as long as possible. This way our models trim doesn’t change or drift with age. We want to minimize the results of vibration, and we want the servos to be as accurate and precise as possible.
For servos the minimum requirement in my mind for the servos in this size model is above the standard sized servo. A premium sport or high torque sport servo is a the minimum needed in a 90-120sized model. The model is larger and has way more power than your standard sized 40-60 size sport model and the loads are going to be greater. So here is my personal opinion on servos. Servos will have multiple levels of performance. The Ball Bearing versions will be smoother and tend to be more accurate. They will last longer under vibration compared to the non-BB versions. A coreless motor servo will be more precise than a non-coreless motor servo. The coreless servo will also tend to last longer as the servo motors are better under vibration and they maintain their accuracy longer. A digital servo will hold accuracy and be stronger at holding it position better than a non-digital servo. The servo market today has a huge selection of servos that have nearly every possible combination of these features. The higher priced servos will be the digital-coreless, and have ball bearing support for the output shaft. Let me say this up front. You can almost never have too much power, too fast, or too precise a servo. The choices that you make on servos will really affect the way the model flies. That doesn’t mean you need to spend $100 per servo…but you should know the choices you make will affect the flying quality of the model.
I’m going to do a Good-Better-Expert setup for servo choices. I will also let you know which servos I’m using on my model. You can mix or match the servo choices in these G-B-E setups to suit your needs. Below I’ll discuss the servos needs of each surface and then we’ll get to the choices.
Ailerons are very important. Probably in most cases the most important servos. A poor choice on ailerons can affect not only rolling maneuvers but loop tracking, and even flying straight and level. For ailerons I would suggest the most accurate servo you can afford. It doesn’t need to be super strong but accuracy is very important. I would say for ailerons torque is a minor concern. You want to have accuracy to help loop tracking maintain level flight and to have accuracy in rolling maneuvers. This is the place, if any, servos should be digital the wings should. When pulling a loop the servos need to hold those ailerons as accurately as possible. Digital servos may have a lower overall torque rating but the fact that digitals servos are better at holding position this is why the digitals thrive in this application. Does it need to be a digital? No…but it needs to be an accurate and precise servo. For ailerons the order of importance is precision, speed, and then power.
Rudder servo choice is the one surface where we need to have some power. I think it’s probably a safe bet to say we want to get up near 90-100in-oz or torque. We might be able to get away a little less if the servo is a digital as it holding power is better. But for the most part on rudder for a pattern model we want some power. The servo should be precise but it’s not as critical as ailerons. For rudder needs power first, precision second and speed last. This is where an older generation high torque analog servo will work very well.
Elevators on this model are a place to play with some choices. Since the model is setup stock for a dual elevator servo…chances are power is not going to be an issue. A single elevator servo on model like this would be around 50-70in-oz. So by the time you add two servos one for each side the result is just about any servo could work for power. However since we want to loop straight with dual elevator servos we want precision, precision, precision. We will need to match up two servos to move the same all the time. This will change as the model ages and vibration creeps in. Speed and power are not super critical back here but we do want the precision. A speedy servo will aid in snaps and making minor pitch corrections. The result is precision, speed, and power in the important order.
Throttle is also an important control. In today’s world of pattern flying managing the throttle is probably the most important thing you can learn. Even guys that are at the top levels can struggle with this. For me the throttle servo needs to be precise, power is not a big deal but needs to be there. Speed is a really low priority on the throttle servo. The 4 stroke engines have such a quick and clean throttle response that servo speed is not a big deal and there are many pilots that will actually choose a slower servo to give them a smoother throttle feel. So the order is precision, power, speed. Another option is many pilots prefer an analog servo on throttle. This means that the vibration of the engine and being directly connected to it won’t cause the servo to fight itself to death. I’m not one of those that feel what ever moves the linkage is a good throttle servo. In most cases you can downsize to a small servo, but I caution that the throttle servo will take the most abuse from vibration. The smaller the servo the more vibration will affect it over the long life of our model.
The next thing to consider is gear sets. A metal gear set is strong but will wear with vibration. The nylon gears will handle the vibration well and this model will not have the high flight loads from a larger 3D style model. So we don’t want metal gear servos. The nylon gears are plenty strong and durable under vibrations. JR now makes some of their digital high end servos with metal or nylon gear sets. The “SA” tag on the end of the servo means “Special Application” and denotes the nylon geared versions of these servos. You want nylon geared servos on this model..
< Message edited by Troy Newman -- 10/1/2007 6:27:47 AM >
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RE: Focus Sport 110 YS Powered - 
