oldfart
Elite Veteran
Location: Vancouver, Canada
| servosAs most beginners are more concerned with acceptable performance at "budget" pricing then on top performance at higher prices I only would like to say that a servos requirements in order of importance are:
1- In all helicopter installations from beginer to expert the most important spec, and one that is not given by any manufacturer is the "reliability" factor. This means the ratio of servo failure to hours of servo use. This is of prime importance because a sloppy servo will only increase ones "workload" to fly precisely. But a servo that fails will cause the inevitable sphincter tightening that leads to the inevitable wallet loosening. 
So for a beginner who is not so concerned with the other aspects and is using an easy to control heli like the Hawk I have found the Futaba S-148's to be one of the most reliable servos in the "budget" class. And will work acceptably well in this application on every control.
NOTE: one will have more fun FLYING his heli with reliable inexpensive units then he will have LOOKING at his heli on the workbench will waiting for more money to purchase higher priced equipment
2 - Durability factor- for all flyers, this is the next important and is the ratio of the amount of slop that will develop over a specific time in use. This is why properly molded gears and DUAL bearing support becomes important. What? Dual bearing supports? Many budget servos advertise "ball bearing servo". They may only have one bearing supporting the servo output shaft so that they can advertise this questionable "benefit". Actually it can be a disadvantage in terms of durability. As the bearing will inevitably be inserted at the top of the shaft, what is supporting the bottom of the shaft? Here you may find anything from the plastic case molding to a harder nylon bushing to a better oilite bushing. In all cases, by putting only one bearing on top, more of the forces will be transfered to the bushings which may well be a plastic or nylon one. In this case, wear will develop a lot faster then in a servo with two harder oilite bushings. So unless the servo has two bearings, its durability factor may not be as good as another servo without bearings. Not to mention that servo "A" with the two oilite bushings may have more accurately molded nylon gears which will remain slop free and drag free for a lot longer then one with poorly molded pastic units.
3 - precision - this area also concerns gear molding accuracy but also motors and electronics. A coreless servo CAN (but is not always neccessarily so) be designed to be more precise then a 5-pole motor or a 3-pole unit. The more precise the servo, the less corrections one will continually have to make so the less work it will be to fly. But a badly designed and manufactured coreless motor can be an accident waiting to happen, and the inexpensive 3-polar would have been the better choice (see. the discussions in here on one major brands problems with one of their expensive series of digital servos).
5 - drivers - the digitally driven servo will have a lot more "holding power" and accelerate to speed at least 5 times faster then an analogue unit. So on your gyro you will find a 3 times slower (0.22 seconds) digital servo with a coreless motor will work better then a much faster (.06 seconds) analoque unit. This is true even when using the most basic type of piezo gyros. (as above, this is all presupposing reliability)
So after all of this one can conclude that the marketing hype and numbers are of very little real practical use except to compare similar product. e.g. the 3000 series Futaba servos to other 3000 series Futaba servos, the 500 series of JR servos to other 500 series of JR servos or 500 series of HiTech servos to other 500 series Hi-Tech units.
So how to use these numbers? As a rule of thumb, if you are comparing apples to apples, then speed is of greater importance then torque in the throttle and gyro/rudder application with torque taking preference in cyclic and collective applications, with 45 in/oz a minimum here for any 30/46 class helis and 60 in/oz for 60 class and 70 in/oz for 80/90 class units.
So after all that verbal dyhrea, the answer is that anything as good as or better then the basic dependable Futaba S-148 is all you will need for training on your Hawk Sport. As some budget servos are far more dependable/reliable then others, just be sure to choose proven reliable units. (note, here have been discussions on the net on some less relaible lower priced servos also.)
Phil |
). Are you trying to avoid a flame war and state your opinion at the same time?
