telemetry causes servo chatters

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Oct 11, 2018
2
0
#1
Recently I switched to Taranis X Lite. I like it a lot, except for one thing: when telemetry is on, the servos may chatter. No visible movements, just making noises. It happens with X4R, RX6R, and G-RX6.

On one of my slopers with Hitec analog servos, I fixed the chatters by moving around the cables.

I have not been able to fix the chatters on my Ahi with Emax digital servos, especially the wing servos, with their long cables. Fortunately I don't need telemetry for Ahi so I just turn it off.

The real problem is with my Snipe 2 and its four MKS DS75K-N digital servos. I poked two holes on the carbon fuselage to let out the pair of antennas, but the servos still chatter. The chatters stop when I pinch one of the antennas between my fingers. The chatters also stop when I turn off telemetry, but unfortunately I need to monitor the voltage for this single-cell lipo setup. For now I have to keep using its old AR6270T (after I have spent several evenings with OpenTX to program this DLG... :( )

I don't need full-range telemetry. Any ways to reduce its power?

Thanks,
Haoyang
 

Konrad

Active member
Jan 23, 2018
636
38
San Francisco
#2
Where do you come from, I assume Spektrum?

What leads you to think this is a problem? In the old day with analog amps yes noisy servos where an indication of a problem. But with digital servos not so much. Digital servo can respond to much smaller changes in the pulse train (I'm assuming you are using PWM). This means that modern RX can set the dead band and resolution very tight to get the most from these digital signals.

I had much the same issue with a (All) my G-RX8 RXs only to find there was no issue as there was no noticeable change in current with the noisy servo verses the quiet servo installation. My in-flight current measurment is accurate to 50 mil-volts.
https://forum.alofthobbies.com/inde...wm-mode-continuous-digital-servo-chatter.452/

It sounds like you have correctly traced this "problem" to noise on the signal wire/antennae. If there is no noticeable current draw (change), fly as is. This is an indication that the the dead band is a little to tight. I think MKS even advertises this very tight dead band as a good thing. :rolleyes:

All the best,
Konrad
 
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Oct 11, 2018
2
0
#3
Where do you come from, I assume Spektrum?
Yes. Since AR6115e and AR6255, their receivers have grown more and more bulky, as if they were selling the receivers by weight. :p

Thank you for the pointer to the earlier thread on this topic. It is very informative.

It would be difficult to compare current draws between telemetry on and off: Even disregarding the servo chatters, telemetry itself will increase the current draw, right?

I was more afraid of the chatters shortening the mechanical life of the servo's gear train, but have no proofs to that, so maybe you are right, and I should just go out and fly it. I have made this cool special function: When triggered by the down elevator at the end of the launch climb, it will announce the launch height.

Thanks again,
Haoyang
 

Konrad

Active member
Jan 23, 2018
636
38
San Francisco
#4
LOL, about Spektrum weight.

Yes, it takes power to transmit telemetry. I assume you were concerned with the servo's current draw over heating the servo's amplifier and failing the chattering servo. Not any real concern with the onboard RX battery. If you put the current sensor between the RX and the servo you will get a comparative reading minus the telemetry power. From my experience I can't measure (see)the increased servo current draw as it appears to be less than 50 milliamps.

Yes, I'm sure the noisy servos are drawing more current than the quiet servo. But I don't think it is significantly more than the quiet servo.

The only time I've ever really prematurely worn out the mechanics of a servo was on helicopter swash plates. I normally strip the servo gear train as a result of impact or flutter.
 
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