17th March 2010

RC Hobby Servo – Chatter

Question: I have a servo that “chatters” and twitches, any idea what is causing this?
Answer: This can be caused by a variety of different things.
1) The servo may be dirty or have had water get into it. In most cases this is fixable by a technician but it is hopelessly uneconomic to pay someone to repair standard servos given their prices today.
2) The servo may have been or is being subject to lots of vibration. This is usually related to an out of balance prop, spinner, engine or motor or mounting the servo without the vibration isolating rubber grommets or cinching down the servo mounting screws too tight or failing to install the brass ferrules to prevent grommet compression.
3) Electrical interference being picked up by the wiring between the servo and receiver . If the leads are long (particularly if you are using extensions) they serve as a form of antenna and can pick up signals from sources including sources both internal and external to the model. Internal sources are typically metal on metal control rod connections or other metal to metal couplers. Electric motors (particularly brushed motors) and speed controls (mechanical or electrical) are also common sources of electrical “noise”.
4) Electrical interference being picked up by the receiver antenna and relayed through the receiver to the servos. Antenna’s that are cut or not properly routed around electrical sources (keep your antenna away from a brushed electric motor) are common sources of such interference. Old noisy automobile ignitions in the area of your receiver are another source of such interference.
5) Bad information coming from your transmitter and being faithfully passed from your receiver to the servo.
6) With the points above, we have probably hit on the 90% of common causes. The final 10% is hard to nail down with a few points. Think dirt, think water, think sources of electrical noise, think vibration.
Troubleshooting:
Keeping these causes in mind we suggest the following troubleshooting approach:
a) Figure out when the servo chatters. Has something changed recently? Has the servo been crashed or dunked? Has it chattered from new or just started recently? Does the servo chatter all the time when it is powered up? Only when the receiver is turned on but the transmitter is turned off? Only when the receiver and transmitter are both turned on? Only when operating your engine or motor? Only when the model is moving? Only when the model is free to move or even when the model is held firmly.
b) Is the noisy servo the only servo in your model that chatters? Does the noisy servo chatter regardless of which channel or extension lead you connect it to? If you replace the noisy servo with another servo of the same type and connect this replacement servo to the same lead and channel, does the replacement servo chatter also?
c) Remove the servo from the model. Connect it directly to a known good receiver. Does it still chatter?
The idea here is to use common sense and some simple trial and error tests to narrow down the cause of the problem. If the noisy servo appears to chatter regardless of where you install it and under all operating conditions then you are probably best off to chuck the servo and go with a replacement. If however, the servo only chatters under some conditions and other similar servos also chatter when exposed to the same conditions, try to locate the source of the interference and eliminate it.

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17th March 2010

How to choose a new/first plane

How to Choose a New or First RC Airplane

How to choose a RC airplane is a frequently asked question on forums. It is a relevant question not only when you are deciding to buy your first plane, but all along the journey, as you acquire a fleet. Many planes are similar, so getting them is kind of useless if you already have one from the same category. Everyone prefers a diversified fleet, and probably will add several planes and drop others along the way. The beginner’s temptation (not only beginners…) is to buy many planes, as they all look so nice. DON’T!!! Many people will regret it and discover that the purchase is not really what they wanted, or is just not adding any more fun to the existing fleet.

What are the angles to think about?
1. Type of equipment necessary for this plane
2. How difficult it is to build
3. How difficult it is to transport to the field
4. How difficult it is to fly
5. How much flying time it has
6. Do you live near a location where you will be able to fly it
7. Money you want to spend

Let’s review these one by one:

1. Type of equipment necessary for this plane

Think about buying equipment that will be reusable with other planes. For example, avoid planes with batteries or receiver/radios that are compatible with only one plane. Check that the radio equipment is compatible with your country allowed frequencies. Check that the frequency won’t disturb anyone at the place you plan to fly. Think about how it will be, if you discover that this hobby is just not for you and decide to resell.
If buying a new RC airplane, and you already have some batteries, you should look into a model that will be compatible with your existing batteries/ESC/motors.

2. How difficult it is to build

If you are not familiar with building methods, choose an ARF (Almost Ready to Fly), and choose an easy one. Some “ARF” are complicated to build, and take many hours. So ask the vendor, Ezone, before buying a particular model. Building a plane can become hell very quickly and there is the risk of never flying properly if built improperly, so ask your questions upfront and do your research. In general, most ARF are ok.
From my own experience, my recommendation for a first RC airplane would be a foam plane that is easy to build with Epoxy or Cyano (verify that it is compatible with the material, before you start gluing). Foam ARF airplanes are also easy to repair… which is essential for beginners.

3. How difficult it is to transport to the field

Never forget you’ll need to carry your airplanes from your home to the flying field. Too many big planes, or planes with wings made of one single piece will be inconvenient to carry. When you choose the size of your plane, I always recommend to take the one with the biggest wingspan, but still not too big: 90 cm to 1.4 meter is good (35.4 to 55.1 inches). A plane measuring 2 meters, but with 2 wings of a meter each, is also a fine.
We all spend a lot of time to make these planes look good, then we fly them carefully to avoid crashes, yet during transport, while in the car, or carrying them around the house, they get hurt….
This can be a very frustrating moment when it happens!

4. How difficult it is to fly

Small planes, even the very nice ones that are easy to carry, present a problem because they often are not easy to fly. They are very nervous, sometimes too nervous, and are not easy to see while flying. I would not recommend anything less than 90 cm (35.4 inches) in wingspan.

Ailerons or no ailerons? There are two schools of thought here. The first one asserts that ailerons/elevators with very small extensions of the servos provide good control and shorten a pilot’s learning curve. The second one believes that using only rudder/elevators for starting is easier and safer.
My personal experience tells me that both are fine, and ailerons are nice to have if well configured. Ailerons provide more control and maneuverability on an RC airplane.

5. How much flying time it has

Some RC airplanes, especially the small ones, can’t accept big batteries, and are limited to a certain space/weight. However, since they are also light, their flying time may not be shorter. In general, before you buy anything, check that the flying time, using the standard setup, provides a minimum of 4 minutes, full speed, and 6 minutes with throttle management. 10 minutes will be even better! Any flying time below that won’t provide a beginner with much pleasure.

6. Do you live near a location where you will be able to fly

Buy an RC airplane that suits your lifestyle. Don’t purchase a plane that needs to take off from the ground, if you don’t have a proper runway to use. Don’t buy a plane, which is too light, if you plan to fly it outside, knowing it will be windy. Along the same line, don’t buy a big plane that needs space, if you plan to fly indoors.

7. Money you want to spend

When you start this hobby, it is important to know the overall cost of a complete system, ready to fly. All the standard equipment is covered in the next chapter, Start in Electronic Flying. The cost for a basic setup could be around $300, all included. Out of this total, we can assume that the plane, motor, props and the servos are not reusable. However, the radio receiver, battery, and ESC can be used for other planes, to leverage the investment.
You may also have the option, depending on your budget, to purchase a second hand configuration.

Sam Huang is the proprietor of EnjoyHobbies.biz, an online RC hobby shop.

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