JR 8231 servo chatter
09-01-2003, 05:08 PM
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JR 8231 servo chatter
Hello all
I am installing 2 rudder servos (JR 8231) on1/4 scale Wagstaff GP extra 300. 4 cell Nicads, and JR 955 PCM receiver. I am getting scary bench top chatter of the rudder (with either one or both servo hooked up) that can be made to go away by damping the rudder on its hinges (such as holding very lightly with finger tip). I assume this is due to servos hunting for neutral, and experiencing resonant flutter. I can also make it go away by setting up the linkages (or servo trims to one or both servos) to give the servo a static load with the rudder in neutral, but this is obviously sub optimal, and I am thinking this is unsafe to fly?? If I tweak the servo with just a blank servo arm installed (no linkages) - I do not get the chatter. The servos have been used before , did go through a crash, but no direct contact / damage.
Appreciate thoughts - is this a sign that the servos are damaged? It will cost me 200$ to replace them, so I am reluctant to must chuck them, but seems unsafe to fly?
Thanks for comments
RJ Miller
I am installing 2 rudder servos (JR 8231) on1/4 scale Wagstaff GP extra 300. 4 cell Nicads, and JR 955 PCM receiver. I am getting scary bench top chatter of the rudder (with either one or both servo hooked up) that can be made to go away by damping the rudder on its hinges (such as holding very lightly with finger tip). I assume this is due to servos hunting for neutral, and experiencing resonant flutter. I can also make it go away by setting up the linkages (or servo trims to one or both servos) to give the servo a static load with the rudder in neutral, but this is obviously sub optimal, and I am thinking this is unsafe to fly?? If I tweak the servo with just a blank servo arm installed (no linkages) - I do not get the chatter. The servos have been used before , did go through a crash, but no direct contact / damage.
Appreciate thoughts - is this a sign that the servos are damaged? It will cost me 200$ to replace them, so I am reluctant to must chuck them, but seems unsafe to fly?
Thanks for comments
RJ Miller
09-02-2003, 03:43 AM
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JR 8231 servo chatter
Might just be normal Pot wear.
Is the jittering just in one spot or throughout the whole range? Try adjusting the linkage and output arm a few teeth away on the output spline of the servo, then change subtrim in your radio. If this fixes it, you have a worn spot on the pot. You might be able to live with this awhile.
If problems are throughout travel, probably still the pot.
Send it into Horizon for new pots and a checkup. They are usually very cheap.
Is the jittering just in one spot or throughout the whole range? Try adjusting the linkage and output arm a few teeth away on the output spline of the servo, then change subtrim in your radio. If this fixes it, you have a worn spot on the pot. You might be able to live with this awhile.
If problems are throughout travel, probably still the pot.
Send it into Horizon for new pots and a checkup. They are usually very cheap.
09-02-2003, 03:53 AM
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Thanks
Hello Mo
Thanks for your comments. It does occur mostly near neutral, but not exclusively. I tried your suggestion, but did not seem to help. I think sending then in is a good suggestion, and I am pleased to hear that Horizon can perhaps repair this rather than pitching these pricey servo.
Thanks again.
RJ Millwe
Thanks for your comments. It does occur mostly near neutral, but not exclusively. I tried your suggestion, but did not seem to help. I think sending then in is a good suggestion, and I am pleased to hear that Horizon can perhaps repair this rather than pitching these pricey servo.
Thanks again.
RJ Millwe
09-02-2003, 04:00 AM
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JR 8231 servo chatter
From all my years of experiance, I can say that probably 95% of servo problems like yours are caused by pot wear.
The only problem for us modelers is, these pots are not available at any old Radio Shack. Have to send them into their maker for the right pot. In this case Horizon. That is good for you, Horizon treats it's customers well.
The only problem for us modelers is, these pots are not available at any old Radio Shack. Have to send them into their maker for the right pot. In this case Horizon. That is good for you, Horizon treats it's customers well.
09-05-2003, 12:09 AM
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servo jitter woes
Thanks Mo. But here is something interesting. I sent the 2 RJ 8231s in for service per your advice and bought two new ones. Fresh out of the box, exact same thing with both rudder servos (either working independently or both hooked up to rudder on opposite sides) --non stop resontant like jittering. This is not a subtle thing, rather jitter is high speed rudder moving 1 inch side to side - will not dampen without touching with finger. I then tried RJ 8417 with same result. There must be something about the mass of the rudder or whatever that encourages this uncontrolled "hunting" about the zero point. I am stuck. I am wondering if yet another type of servo might work better, or perhaps some type of damping "spring" arrangement. Looking for suggestions!!!
Thanks for any suggestions from you or others.
RJ Miller
Thanks for any suggestions from you or others.
RJ Miller
09-05-2003, 01:45 AM
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JR 8231 servo chatter
HD,
I had an identical problem with the 8231's that run the elevators on my 27% WM 300S. I cured it by replacing the elevator horns with new pieces... a small amount of wear that had accrued in the horns was allowing the servos to start hunting, then resonate into an estimated 10-20 hertz, 1/2 inch deflection. So my advise would be to look closely at the linkage for any looseness whatsoever.
Gary
I had an identical problem with the 8231's that run the elevators on my 27% WM 300S. I cured it by replacing the elevator horns with new pieces... a small amount of wear that had accrued in the horns was allowing the servos to start hunting, then resonate into an estimated 10-20 hertz, 1/2 inch deflection. So my advise would be to look closely at the linkage for any looseness whatsoever.
Gary
12-11-2003, 02:57 PM
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RE: JR 8231 servo chatter
You may need a noise filter for long servo leads. They are cheap $12 or can be home built.
check my website under 'R/C Gadgets' for circuit diagram...
http://www.uoguelph.ca/~antoon
check my website under 'R/C Gadgets' for circuit diagram...
http://www.uoguelph.ca/~antoon
12-11-2003, 03:49 PM
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RE: JR 8231 servo chatter
On a second note for the same JR DS8231 servo, I have a questio of a different nature:
I just purchased a new JR PCM10X system, which comes with 4 of these 'ultra digital' servos. I was in need of modifying all of them to be used with a special project for our local University's Land Resources Dep. I do this job as a special project. I needed contineous rotation of all servos so I removed the 5K pots and substituted with a 2 fixed 2K4 resistors to give the servos a 'load'. All works fine except I can't stop the servos from 'creeping' when a position is selected.
This system is used with a tethered blimp which hangs about 300-500 feet in the air and makes pictures in infra-red, heat, and ultra violet models of the soil. The servos are used for pan/tilt/on-off/ and horizontal movements of the cameras.
How do I stop the servos from creeping? The radio and gyros allow for adjustments and do a great job just that after all the adjustments the servos are still movin'. Any ideas in solving this problem? Caps? I'm a certified electronics technologist... :-)
I just purchased a new JR PCM10X system, which comes with 4 of these 'ultra digital' servos. I was in need of modifying all of them to be used with a special project for our local University's Land Resources Dep. I do this job as a special project. I needed contineous rotation of all servos so I removed the 5K pots and substituted with a 2 fixed 2K4 resistors to give the servos a 'load'. All works fine except I can't stop the servos from 'creeping' when a position is selected.
This system is used with a tethered blimp which hangs about 300-500 feet in the air and makes pictures in infra-red, heat, and ultra violet models of the soil. The servos are used for pan/tilt/on-off/ and horizontal movements of the cameras.
How do I stop the servos from creeping? The radio and gyros allow for adjustments and do a great job just that after all the adjustments the servos are still movin'. Any ideas in solving this problem? Caps? I'm a certified electronics technologist... :-)
