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MKS777 servo jitters

Old 05-29-2019, 03:01 AM
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gunradd
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Default MKS777 servo jitters

Hello all.
As most know I do allot of builds for guys and also tech support for Pacific Rc Jets. I have been running into issues on several planes with MKS servos with long servo extensions. One is a skymaster viper XXL with all MKS servos. When you go full deflection on the stick the servo will go full travel then bounce back quickly and resume back to full deflection. I thought I had an isolated problem on this plane but after dealing with a few others they had the same exact problem. The fix so far is to remove the MKS servos and install another brand. I have tried changing voltages on the receivers with no luck also. Higher gauge wire did nothing . This has now happened with a jetti setup a spektrum setup and a futaba conventional set up. Think the servos where all MKS 777. So if your setting up a plane and see this jitter now you know. I would not use the MKS 777s on long extensions. Not sure if when using futaba if Sbus will make any difference for those dealing with this issue.
Old 05-29-2019, 03:28 AM
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Len Todd
 
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Have you measured the actual voltage at the servo connection to the extension at full deflection? The MKS may be sensitive to the voltage drop. But it may also indicating that there is a significant voltage drop which is probably the cause of the symptom you are seeing. The root cause of the voltage drop could also affect the other brand servos, but maybe in another way not so visible on the bench, but could show up in flight. Best to figure out how to eliminate the voltage drop. If the MKS servos operate correctly on a short harness, then you definitely have a power supply issue (vs. a servo issue) someplace. Maybe the Rxer buss just can't handle the power demands, maybe the line loss is just too much for the servos. You did not mention if you were using power distribution boxes or just running off the Rxers. It is hard to get the power you need for a giant plane thru a typical Rxer buss even w/o long harness extensions. Every connector adds to the loss.

There are a couple threads on this forum discussing solutions to this particular issue.
Old 05-29-2019, 03:29 AM
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BarracudaHockey
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What extensions are you using? The guys that have fixed them with extensions are using the heavy duty stuff from PowerBox

Also the power safe receivers have a firmware update to help mitigate the issue.
Old 05-29-2019, 04:21 AM
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tp777fo
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Chris. I had the same problem in my FB T33. Tail servos jittered uncontrollably with a little stick "stirring". Tried Powerbox HD and Extreme Flight 20 gauge. The Extreme Flight leads solved the problem. The issue is low signal voltage. It was verified by both Danny at Aeropanda and Thomas at MKS. My tail leads are almost 7'. The new leads cured it. Thomas said he could reprogram the 777s but no issues with the new leads. These are all I use now for long extension's.

For Jeti users a new setup with a CB400 main hub and giant gauge extensions to CB100s in the tail and wings. I saw it at Joe Nall and am thinking of changing my T33 to this over the winter. Another plus is there are only 2 plugs for atraching wings. Power and signal.

Last edited by tp777fo; 05-29-2019 at 04:25 AM.
Old 05-29-2019, 04:43 AM
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Blinky
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Had the same problem and same answers, j fix the problem and recommend u try this, electro dynamics sells a signal buffer booster, installed at the servo lead all problems go away. The unit cost 12$ each.
Old 05-29-2019, 04:45 AM
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U can call me Dwayne 773.507.8534
Old 05-29-2019, 09:18 PM
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JoeJr1485
 
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Originally Posted by gunradd View Post
Hello all.
As most know I do allot of builds for guys and also tech support for Pacific Rc Jets. I have been running into issues on several planes with MKS servos with long servo extensions. One is a skymaster viper XXL with all MKS servos. When you go full deflection on the stick the servo will go full travel then bounce back quickly and resume back to full deflection. I thought I had an isolated problem on this plane but after dealing with a few others they had the same exact problem. The fix so far is to remove the MKS servos and install another brand. I have tried changing voltages on the receivers with no luck also. Higher gauge wire did nothing . This has now happened with a jetti setup a spektrum setup and a futaba conventional set up. Think the servos where all MKS 777. So if your setting up a plane and see this jitter now you know. I would not use the MKS 777s on long extensions. Not sure if when using futaba if Sbus will make any difference for those dealing with this issue.

i had had the same issue in my FB viper that I built. I even posted YouTube videos search for MKS 777 issues and it should come up. I had the issue running them on the CB200. I did some testing and hooked up a 12 channel and the problem seemed to stop. I thought it was only on the rudder servo then the ones that I had on the flaps started to do the same thing. Switched out the servo wires and still didnít fix it. So I have 6 MKS servos that I am not using. This was 4 years ago.

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