Servo jitter and crosstalk
Servo jitter and crosstalk
I've fitted RC to a couple of batter locos, but I'm basically new to it and haven't used servos before. I've been working on the RC for my Regner Konrad. and have hooked up the servos (Tower MG90S) to the receiver, a Deltang Rx 102. Everything works, but the servos jitter - it's hard to see, but it's audible. There is also some crosstalk (when one servo operates, the others move very slightly). None of this is actually preventing the system from working, but I'm wondering it means (a) faulty servos (b) faulty receiver or (c) it's just normal behaviour. If (a) or (b) I'm not sure whether it matters other than it might shorten batter life.
I'm not sure the following video is very illuminating really, the crosstalk is hard to see, but you can just see the tiny movement when an out of shot servo is operated (twice each way) and you can maybe here the jitter.
Today channel 1 on the receiver also seems to have stopped working which makes it seem that (b) is the most likely option, but I don't have another Rx102 on hand at the moment to swap in to test that theory...
Anyone experienced anything like this?
I'm not sure the following video is very illuminating really, the crosstalk is hard to see, but you can just see the tiny movement when an out of shot servo is operated (twice each way) and you can maybe here the jitter.
Today channel 1 on the receiver also seems to have stopped working which makes it seem that (b) is the most likely option, but I don't have another Rx102 on hand at the moment to swap in to test that theory...
Anyone experienced anything like this?
- bambuko
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Re: Servo jitter and crosstalk
Have you done anything to the RX antenna?
Does it happen with servos and receiver just connected on the bench (i.e. outside of the loco).
It's not likely to be faulty servo.
It is not a normal behaviour.
It matters - if it is that bad with transmitter only few feet away from the receiver, imagine what it will be like with loco some distance away and with obstruction to the signal...
I would take it all out of the loco and test with only one servo connected (are the symptoms the same?).
Then connect another servo (one only again) and only then connect couple of them.
That will confirm whether it is one dodgy servo, whether it is interference from battery (any bad/arcing electrical connections?).
Have you got another receiver to test it with?
Servo testers are very cheap and will allow you to test things without a radio.
Do it properly
and p.s.
your video is fine and clear demonstration of the problem
Does it happen with servos and receiver just connected on the bench (i.e. outside of the loco).
It's not likely to be faulty servo.
It is not a normal behaviour.
It matters - if it is that bad with transmitter only few feet away from the receiver, imagine what it will be like with loco some distance away and with obstruction to the signal...
I would take it all out of the loco and test with only one servo connected (are the symptoms the same?).
Then connect another servo (one only again) and only then connect couple of them.
That will confirm whether it is one dodgy servo, whether it is interference from battery (any bad/arcing electrical connections?).
Have you got another receiver to test it with?
Servo testers are very cheap and will allow you to test things without a radio.
Do it properly
and p.s.
your video is fine and clear demonstration of the problem
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- Cleaner
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Re: Servo jitter and crosstalk
I had this when fitting R/C with separate regulator and reverser servos to a Ragleth. If I remember correctly, when the throttle servo was under load it would affect the reversing servo. I fixed it by putting the wiring from one of the servos through a ferrite ring a couple of times, something like this:
The ferrite I used was salvaged from an old power supply. You can also get clip-on ones.
The ferrite I used was salvaged from an old power supply. You can also get clip-on ones.
Re: Servo jitter and crosstalk
Thanks for the replies!
No - or at least, not intentionally.
It still happens on the bench. I've tested this by removing the receiver from the loco and connecting it to another couple of servos from the same batch (just to save unmounting the ones on the loco). Same thing. But - I also tried hooking up an SG90 (plastic gears) and that doesn't seem to jitter or be affected by the crosstalk...Does it happen with servos and receiver just connected on the bench (i.e. outside of the loco).
It's not likely to be faulty servo.
It is not a normal behaviour.
I have tested with the transmitter a few feet away, and with it several metres away, and seen little difference in the effect.It matters - if it is that bad with transmitter only few feet away from the receiver, imagine what it will be like with loco some distance away and with obstruction to the signal...
With one servo connected there are no symptoms. With two connected, there are. (No arcing or bad connections as far as I can see).I would take it all out of the loco and test with only one servo connected (are the symptoms the same?).
Then connect another servo (one only again) and only then connect couple of them.
That will confirm whether it is one dodgy servo, whether it is interference from battery (any bad/arcing electrical connections?).
No, but I can see I'm probably going to need to get another one, since channel 1 on this one hasn't recovered!Have you got another receiver to test it with?
I have now tested with a servo tester (why didn't I think of that?) and the jitter isn't there; can't see a way of testing for the crosstalk, but the rx is starting to look very much like the culprit.Servo testers are very cheap and will allow you to test things without a radio.
Thanks I'll have a look for something suitable.metalmuncher wrote: ↑Sat Dec 07, 2019 1:49 pm I had this when fitting R/C with separate regulator and reverser servos to a Ragleth. If I remember correctly, when the throttle servo was under load it would affect the reversing servo. I fixed it by putting the wiring from one of the servos through a ferrite ring a couple of times, something like this:
The ferrite I used was salvaged from an old power supply. You can also get clip-on ones.
- bambuko
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Re: Servo jitter and crosstalk
Yes, I think you have narrowed down the problem.
If it was servo problem it would also be a problem with servo tester.
Whether it is dodgy receiver or simply interference (more likely in my view) is another story.
Second receiver will help in confirming
- tom_tom_go
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Re: Servo jitter and crosstalk
Send the Rx back if you suspect it of being faulty.
Have you tried different batteries in both the Tx and Rx?
Have you tried different batteries in both the Tx and Rx?
Re: Servo jitter and crosstalk
Try metalmuncher's idea with the ferrite ring. Could help.
Rik
Rik
Re: Servo jitter and crosstalk
Thanks for the replies - today has shot by without a chance to have another play with this problem. I haven't got a spare Tx battery to hand, but I recharged the Rx batteries. Then my next steps will be (a) get another Rx102 as I need another one anyway, and then I can compare directly by swapping, and (b) get a ferrite ring and see if that improves things. Will keep you posted.
- tom_tom_go
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Re: Servo jitter and crosstalk
I have some second hand Rx102's, PM me if interested.
Re: Servo jitter and crosstalk
Brief update: With new (s/h) Rx102 from tom_tom_go there's no crosstalk. In fact there's no crosstalk anymore with the original receiver. This is puzzling, as I haven't changed anything other than leaving it in a cupboard for several weeks, but hey it works. Plus I've now got a receiver for my next r/c project. There's still a bit of jitter (though it seems less) but I have still to test a ferrite ring so the next step will be to see if that eliminates it.
- tom_tom_go
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Re: Servo jitter and crosstalk
No, that's the odd thing. Same batteries in Rx and Tx. I'd borrowed the Rx batteries for something else so I recharged them. But I'd just given them a full charge before testing it last time...
- tom_tom_go
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Re: Servo jitter and crosstalk
So when the batteries are fully charged you get the jitter?
Re: Servo jitter and crosstalk
I do, but it's distinctly less jittery than it was before.tom_tom_go wrote: ↑Wed Jan 15, 2020 8:00 pm So when the batteries are fully charged you get the jitter?
- tom_tom_go
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Re: Servo jitter and crosstalk
I would replace the battery, are you using single cells or a pack? If you are using AA or AAA batteries then you might have a dodge battery in the mix.
Re: Servo jitter and crosstalk
Rx I'm using 4 AAs in a holder for testing, I will be using 4 AAAs or a pack when it's all done. So maybe next thing is I switch to the AAAs and test with those.tom_tom_go wrote: ↑Thu Jan 16, 2020 11:23 am I would replace the battery, are you using single cells or a pack? If you are using AA or AAA batteries then you might have a dodge battery in the mix.
Re: Servo jitter and crosstalk
Should have posted this in this thread long ago, sorry for the poor etiquette - but it's just come up elsewhere which has made me realise my omission!
The final resolution was: I did replace the batteries as Tom suggested, this did seem to resolve the problem.
The final resolution was: I did replace the batteries as Tom suggested, this did seem to resolve the problem.
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