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.

 

 

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.

 

 

 

Question: What causes servos to make a noise when at "idle"?

 

Answer: This is nearly always caused by a stiff or sticking mechanical connection beyond the servo arm. The servo is trying to return to center when at idle and the mechanical linkage is impeding this so the servo keeps trying.

 

This puts a load on your servo, may cause wear and puts a high electrical load on your servo which will drain your flight pack more quickly than normal.

 

In the case of electrical RC systems that use a Battery Elimination Circuit (BEC) special consideration must be given to eliminating unnecessary loads from the servos. Firstly, such loads are depleting your only battery and this will lead to shorter run times and a early low voltage cutoff of power by the BEC monitoring circuit. Secondly, most BEC's are limited in the total amount of current that they can control. Adding more servos adds to the load. So does adding a bunch of servos that are all pushing on sticky mechanical linkages and working harder than they should. Some BEC's will shut down to protect themselves from overload. Other BEC's simply fail. In either event, your receiver will be without power and you will not be able to control the model if the BEC is not working.

 

Bottom line here is that you should make sure that all mechanical linkages move easily. To test for this we suggest that you remove the linkages from the servo arm. If the humming, buzzing or groaning noise goes away, then the mechanical linkage is binding. Straighten the path, make sure clevises, rods and other connectors are free to rotate in the servo arm holes etc. All control linkages should be slop free but move easily with a light touch of your fingers. Once you have the linkage freed up, reconnect the linkage to the servo and move the servo to and fro across the neutral position. Let the servo return to neutral. The noise should have stopped. If the noise is still present and you are sure that the mechanical linkages are not binding, you have another problem with the servo.