Can servo jitter come from RF module ?

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jmf
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Can servo jitter come from RF module ?

Post by jmf »

Hello,

I had up to now a problem of RF module (see the thread about a pb on PPM signal). Yesterday I replaced the RF module with a new flysky module. I can now control the servos ;-). But some jitter (I'm not sure about the wording) appeared on the different planes (different servos, different Rx). I tried to have the Tx at 2 or 3 meters, and it changed nothing...

I tried to do a small video, but I don't know how to post it in the forum. Here, servos are brand new. There ar no extension chords. There is no perturbating system near...

The only thing that changed is the RF module. Can it be the cause of such behaviour ? How to troubleshoot this type of issue ?

Regards,

JM
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Rob Thomson
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Can servo jitter come from RF module ?

Post by Rob Thomson »

This are micro servos on an Alula?

What voltage are you sending to them? I have seen jitter with too high a power being sent to the servos.


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Crucial
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Can servo jitter come from RF module ?

Post by Crucial »

For video it's probably easiest to upload to YouTube then link to the video here.
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ShowMaster
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Re: Can servo jitter come from RF module ?

Post by ShowMaster »

Just an idea? The ppm signal the drives the modules ppm in might be dirty. Your other posts mention you had ppm issues because of solder connections and added wires and switches plus the resistor to the ppm line if I remember.
it possable your modifications have added unwanted noise to the ppm line?
Also be cause you don't know the history of your eBay FlySky module you have any unanswered conditions to work out to find the trouble.
One option is to reverse your modifications to your ppm line so that it's returned to its original wiring. No wires or resistor on the ppm line, just a wire jumper across the gap you cut in the ppm printed circuit and try the servos again. As also mentioned just 5 v on the rx and servos power as some servos jitter with over 5 v.
I assume you used your original system with the first FlySky module and the same rx and servos and power source with no jitter, correct?
The art of troubleshooting is to have some before and after conditions to compare. One also has to reverse one by one all the modifications one by one until the condition goes away.

Finally having some test equipment to read the voltages and waveforms is a big help.
In your case you have a meter, next make some probes up from small wooden dowels with sharp needles at the ends and wires to go to your meter probes. The needles will dig into the solder and circuit clad and will not slip and short out what you're measuring like blunt probes do. They also fit into tight places better. Use shrink to only expose the tips of the needles. Inexpensive bamboo Skewers are my favorite for probing wire bundles and circuit board solder connections as well as making test probes. In the USA $.99 cent stores have the best price for a bundle but most grocery and food stores have them. Good for pinpoint epoxy jobs as well.
Next search for some free scope programs for your PC or Mac so you can look at your ppm signal and see if the waveform has Mitterrand where it starts. You can also save and post it.
Others here have used these programs and hopefully will post some links and tips on how to use them. That info should have it's own section here.
So, start with going back to your TX's original wiring to see if you built the jitter into your tx or it's the new module or rx power source.
SM
Last edited by ShowMaster on Sun May 06, 2012 3:31 pm, edited 1 time in total.
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jhsa
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Re: Can servo jitter come from RF module ?

Post by jhsa »

My er9x/Ersky9x/eepskye Video Tutorials
https://www.youtube.com/playlist?list=PL5uJhoD7sAKidZmkhMpYpp_qcuIqJXhb9

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ShowMaster
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Re: Can servo jitter come from RF module ?

Post by ShowMaster »

Too bad it's not a kit. Maybe someone will do a review and "how to" on the free scope program. I own 2 scopes I've collected over the years so I'd rather someone else needing one will do the review. Very worthwhile project that many will benefit from.
SM
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Re: Can servo jitter come from RF module ?

Post by ShowMaster »

Getting back to the jitter.
First he has to reverse his mods if the jitter was not there at the start. Because a new module is involved it does muddy up the troubleshooting. Mods, or new module or rx power and servos? Try another brand servo you know is good and doesn't jitter on other systems. You have to have refferances you know are good to start with to narrow down what's causing it.
SM
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jhsa
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Re: Can servo jitter come from RF module ?

Post by jhsa »

It is a kit.. You can get it from here

http://www.dpscope.com
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Crucial
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Can servo jitter come from RF module ?

Post by Crucial »

Looks like the kits are no longer available. Only the premade units. They're about $100 shipped to the US without probes.
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Rob Thomson
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Can servo jitter come from RF module ?

Post by Rob Thomson »

You could get one of those cheep PDA style scopes for less?

I have now bitten the bullet and ordered a desktop scope & function generator.


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jmf
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Re: Can servo jitter come from RF module ?

Post by jmf »

Hello,

So first of all, thanks for your support and the so usefull information provided.

I uploaded the video on youtube: http://youtu.be/QaaRZ4tPzbE. Is this called jitter ?

The servos are HXT500 and HXT900 (it the Alula, it is HXT500)

I fully understand the importance of working step by step and to reverse the modifications when possible.

However, I checked my Rx packs and theu were above 5V (Rx pack unloaded / unplugged). It is 4 AAA NiMh elements. Fully loaded Rx packs can be a problem ? Does this means that I have to stop charging the RX pack before the end. Or accept some jitter at the beginning of the use ?

I also checked as it is easy, the PPM signal out for the Tx through the trainer port to CRRCsim whic has a Test mode that displays the PPM signal => pretty nice.

I discharged one of them to 4.8V yesterday. And this morning, no jitter at all. But at the same time, I had recharged the Tx (from 10V to 10.6V). So now I have to discharge the TX to see if it has some influence on the jitter. Fist time I discovered the jitter, the Tx was at 9.4V.

After all those tests, I'll try to suppress my wire and do a small strap on the PPM signal line (even if it should have no effect).

Kind regards,

JM
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Rob Thomson
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Can servo jitter come from RF module ?

Post by Rob Thomson »

I think this is just a case of the servos not liking high voltage.

Any chance your rx is in 'high voltage mode'.

I had similar issues once on a Fasst rx that needed it's mode changed.


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jhsa
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Re: Can servo jitter come from RF module ?

Post by jhsa »

Crucial wrote:Looks like the kits are no longer available. Only the premade units. They're about $100 shipped to the US without probes.
I was mailing the guy yesterday and understood that both kits are available. and he charges 7€ flat rate for postage..
I mailed him cos I don't know if his software runs in Linux.. There are 2 versions of the scope the version I was interested is the "SE" version which comes with a logical analizer and as far as I understand is cheaper. 39€ I think..
I have two Hamag scopes but they are very old.. one only has one channel and the other has 2 channels but one is broken.. I could try to fix it though.. I wanted this other one for an old PC that I have and want to give it some use.. Hate throwing things in good working order away..
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gohsthb
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Re: Can servo jitter come from RF module ?

Post by gohsthb »

Fasst receivers have a 'high speed' mode not high voltage. Instead of sending servo pulses at the normal ~20msec, they send the servo pulses at 9msec. If you are using analog servos or digital servos that can't handle the faster timing they will get very hot - quickly. There was a guy in my club that had this happen. So on Futaba and Frsky check that the receiver is in the correct mode when you initally bind it before plugging servos in.
-Gohst
Last edited by gohsthb on Mon May 07, 2012 2:03 pm, edited 1 time in total.
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Rob Thomson
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Can servo jitter come from RF module ?

Post by Rob Thomson »

Thanks for the clarification :). Many moons since i used Fasst. Buy I recall the one mode having loads of jitter! Flattened the battery rather fast too!


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