Interference/Servo Noise

[Chris Anthony]

Hi guys,

Sometimes depending on RX orientation in the plane, my throttle and aileron servos (closest servos to RX) will make a buzzing. Like when something is trying to move them and they are resisting. This only happens when the RX is next to them, with RX switched on AND TX switched on.

If I wiggle the antennas of the RX about in this case, or sometimes just touching an antenna, the noise will stop. But whenever I think they are in a position which eradicates the noise, as soon as I let go of them, the noise returns.

TX-Servo control doesn't seem to be impaired, and range doesn't seem to be affected but my questions are:

1. What is the cause of this servo noise?

2. What is the worst-case scenario that could result from this noise/it's cause?

3. Why do the RX antenna's need to be 90 degrees apart from each other?

4. What is the worst-case scenario that could result from not ensuring 3. above is met?

3 and 4 I feel might be related, but to be clear, I do make sure the RX antenna's are always 90 degrees apart. I just don't know why this is recommended.

I'd be grateful if anyone could advise.

Thanks,

Chris

[Bob Cotsford]

informed user opinion only:

1) feedback loops- similar concept to when you put a microphone and speaker close together - 'noise' from the receiver affects the servo amplifier making the servo buzz.

2) it causes wear on the servo, drain on the battery and possibly noise in the receiver that could in extreme cases drown out the transmitter signal, so worst case is loss of control through a flat battery or excess noise.

3) it's to do with polarisation of the transmitted signal and orientation of the aerials and this gives the best compromise of signal strength with the varying attitude of the model - ie it tries to keep one aerial in a reasonable orientation to the transmitter at all times.

4) short range in certain attitudes - as the model turns towards or away from you it loses signal.

[cymaz]

Is the fus covered in silver type covering or carbon fibre.....these might cause interference. A servo buzzing will drain the Rx battery quicker than it should also you might burn the servo out just at the wrong moment of a flight causing a crash.

[Dave Miller]

Digital servos buzz.

[Chris Anthony]

Great answer, especially for 3 and 4. It makes perfect sense. Thanks Bob.

[Chris Anthony]

cymaz and Dave I've only just noticed your comments sorry. cymaz, the fuse is just covered in seemingly standard vinyl wrap, no silver or carbon fibre tape that I've noticed. Dave. They shouldn't buzz when they aren't doing any work.

By the way chaps, this plane crashed tonight due to some kind of radio failure. I'm just about to write up what happened in a seperate post, I'd love to hear your inputs.

Cheers, Chris

[Peter Jenkins]

In my experience, digital servos always buzz!

[Chris Anthony]

I thought I'd post an update on this, as this interference problem seems to be apparent on my new Acrowot model, and has actually worsened to the point where performance is degraded.

In my previous posts, I've described the problem as seen on my Seagull Jumper 25 with 4x Etronix Digital ES092 standard servos. My new Acrowot has 5x Futaba 3001 servos (these are not digital servos).

Basically, the servos will make noise amongst themselves when controlled by the TX/RX on the model, even if not attached to control surfaces (ruling out joint friction problems I've read about before). When making the buzzing noises, the servos are stalled (confirmed by ~0.6A current from them when they buzz). It is not just one servo that this happens to, sometimes it is none, sometimes it can be all, sometimes just one or two.

The performance is degraded on the Acrowot, as I can be moving the control surfaces via the TX for a few seconds with smooth responses, and then suddenly the control surface movements will become all laggy and delayed. It actually seems to me as if a brown-out begins to occur. This is accompanied by the offending servo beginning to buzz and stall. Telemetry shows RX voltage drop momentarily too (not below brown-out voltage, though), even after a full charge.

The problem also seems to correlate with current. I initially used a 6V battery with the RX on both models. When swapping down to a 4.8V battery the problem became worse on both models. When using the 4.8V battery on the Jumper, the buzzing became worse and the same brown-out-ish symptoms as with the Acrowot were also seen on it. Then, I used the same receiver on my tiny little park-flier with micro-servos drawing much less current and there will be no interference/stalling/lack of response at all.

Finally, the Acrowot servos have all been individually tested with a servo tester whilst fitted to the plane. No buzzing, stalling or lack of response occurred

At the moment myself and some helpful guys at the club have therefore deduced it to be a problem with the RX. Has anyone ever come across an RX problem like this before? It is an FrSKY D8R-II Plus (with telemetry).

[Frank Skilbeck]

It sounds like your Rx is set to high sped mode for use with digital servos, this will cause analogue servos to buzz and potentially get hot, have a look in your Rx instructions there should be a way of setting it to regular mode from high speed.

Just had the same happen with a friends plane when using a Frsky Fasst compatible Rx, during binding we had inadvertently held the button down too long and it had gone into high speed mode, once we'd set it back to regular speed it was fine.

Note you can use digital servos in regular or high speed modes, but analogue servos can only be used in regular speed mode.

[Chris Anthony]

Top job, thanks very much Frank. This was indeed the case, I was in high-speed mode. Must have done it when trying to set my fail-safes one time and pressed the button too long. All sorted now; no servo noise and full control! Had a successful maiden tonight! Cheers!