What if the signal wire to the servo disconnects?
08-25-2014, 01:19 AM
#1
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What if the signal wire to the servo disconnects?
Do you have any idea or experience on this topic?
The servo receives supply voltage but at some point during the operation the signal wire has an interruption (maybe due to a bad connector or bad crimp joint). Now how would the servo behave?
- Keep the last position?
- Go to one extreme?
- Get loose, release the pressure on the control surface?
- Other?
Would the behaviour relate to the type of the servo (analog/digital), to the brand of the servo, to the specific model of the servo?
Thank you very much...
The servo receives supply voltage but at some point during the operation the signal wire has an interruption (maybe due to a bad connector or bad crimp joint). Now how would the servo behave?
- Keep the last position?
- Go to one extreme?
- Get loose, release the pressure on the control surface?
- Other?
Would the behaviour relate to the type of the servo (analog/digital), to the brand of the servo, to the specific model of the servo?
Thank you very much...
08-25-2014, 06:02 AM
#2
I would think the servo would stop in the last position and release the pressure on the surface. In other words
it should act the same as if you kept the the receiver on and turned off the transmitter with no type of fail safe
set.
it should act the same as if you kept the the receiver on and turned off the transmitter with no type of fail safe
set.
08-25-2014, 07:37 AM
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I didn't know the answer to your question so I decided to try it.
It would seem the behaviour depends on the Servo, a Hitech Servo froze in position and retained pressure against any movement.
A cheaper servo also stopped in the last position but I was able to move it easily.
https://www.youtube.com/watch?v=Rpn3rnGvKqw
It would seem the behaviour depends on the Servo, a Hitech Servo froze in position and retained pressure against any movement.
A cheaper servo also stopped in the last position but I was able to move it easily.
https://www.youtube.com/watch?v=Rpn3rnGvKqw
08-25-2014, 08:53 AM
#4
I had this happen to me with a digital aileron servo, what I got was full movement either way but in no relation to the stick input. On take off the model went 90 degree roll left then 180 degree right all 20ft off the runway, certainly got the adrenaline pumping.
Fortunately I got the plane back on the deck in one piece. On the bench it took me a while to locate the problem which was the signal lead had just started to come out of the servo plug housing just enough to give a sporadic connection, I'd have thought that the servo (HiTec 5625) would have gone to the commanded position but found that the servo would go to full throw first.
Needless to say I now try and check the pins are in the housings more often having nearly found out the hard way.
Fortunately I got the plane back on the deck in one piece. On the bench it took me a while to locate the problem which was the signal lead had just started to come out of the servo plug housing just enough to give a sporadic connection, I'd have thought that the servo (HiTec 5625) would have gone to the commanded position but found that the servo would go to full throw first.
Needless to say I now try and check the pins are in the housings more often having nearly found out the hard way.
08-25-2014, 12:09 PM
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Thanks a lot for the answers. I also had the opprtunity to make a few tests. I have used an analog Hitec HS325, a digital Bluebird and a digital and programmable Hitec HS5496.
When I retained the supply leads but disconnected the signal wire, the analog one and the Bluebird stopped at the last position but I was able to rotate the servo horn easily. The HS5496 however retained the last position and it was not possible to rotate the servo horn.
Yesterday, I was flying my 80 inch ESM Sea Fury. After a roll to left I centered the aileron stick but the plane continued to roll to the left but with a significantly lesser roll rate. I gave full right aileron input to be able to fly level, then switched from medium to high rate and used rudder to safely bring the aircraft to the runway. After landing everything seemed to work fine! My theory is that one of the aileron servos (which were connected using a Y harness) stopped responding due to a contact problem of the signal wire. During the landing as the plane hit the runway the contact problem resolved spontaneously.
This is why I have started this topic and made this test.
When I retained the supply leads but disconnected the signal wire, the analog one and the Bluebird stopped at the last position but I was able to rotate the servo horn easily. The HS5496 however retained the last position and it was not possible to rotate the servo horn.
Yesterday, I was flying my 80 inch ESM Sea Fury. After a roll to left I centered the aileron stick but the plane continued to roll to the left but with a significantly lesser roll rate. I gave full right aileron input to be able to fly level, then switched from medium to high rate and used rudder to safely bring the aircraft to the runway. After landing everything seemed to work fine! My theory is that one of the aileron servos (which were connected using a Y harness) stopped responding due to a contact problem of the signal wire. During the landing as the plane hit the runway the contact problem resolved spontaneously.
This is why I have started this topic and made this test.
08-25-2014, 06:04 PM
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Thanks a lot for the answers. I also had the opprtunity to make a few tests. I have used an analog Hitec HS325, a digital Bluebird and a digital and programmable Hitec HS5496.
When I retained the supply leads but disconnected the signal wire, the analog one and the Bluebird stopped at the last position but I was able to rotate the servo horn easily. The HS5496 however retained the last position and it was not possible to rotate the servo horn.
Yesterday, I was flying my 80 inch ESM Sea Fury. After a roll to left I centered the aileron stick but the plane continued to roll to the left but with a significantly lesser roll rate. I gave full right aileron input to be able to fly level, then switched from medium to high rate and used rudder to safely bring the aircraft to the runway. After landing everything seemed to work fine! My theory is that one of the aileron servos (which were connected using a Y harness) stopped responding due to a contact problem of the signal wire. During the landing as the plane hit the runway the contact problem resolved spontaneously.
This is why I have started this topic and made this test.
When I retained the supply leads but disconnected the signal wire, the analog one and the Bluebird stopped at the last position but I was able to rotate the servo horn easily. The HS5496 however retained the last position and it was not possible to rotate the servo horn.
Yesterday, I was flying my 80 inch ESM Sea Fury. After a roll to left I centered the aileron stick but the plane continued to roll to the left but with a significantly lesser roll rate. I gave full right aileron input to be able to fly level, then switched from medium to high rate and used rudder to safely bring the aircraft to the runway. After landing everything seemed to work fine! My theory is that one of the aileron servos (which were connected using a Y harness) stopped responding due to a contact problem of the signal wire. During the landing as the plane hit the runway the contact problem resolved spontaneously.
This is why I have started this topic and made this test.
On each of my aircraft / helis / multicopters, when inserting the Servo / ESC leads I put a small amount of "Deoxit" Gold on the connectors. This improves electrical conductivity and also minimises long term corrosion as I used to fly close to a saltwater environment.
You can also secure the servo leads against pulling out, various methods I have used that work are cable ties, tape, heat shrink and even elastic bands. Maybe overkill but I do that with all my builds. You know the old saying, "an ounce of prevention is better than a pound of cure"
Last edited by Rob2160; 08-25-2014 at 06:11 PM.
08-25-2014, 11:17 PM
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Great! 
I am a surgeon and this is my motto during the operations.
There is no connection in my aircraft without a security measure. Usually I use connector caps but sometimes high quality electrical tape or similar. I didn't have the opportunity to check the cables after the incident. The Sea Fury stays at the airfield so I will be able to check it at the next flight day.
I am a surgeon and this is my motto during the operations.There is no connection in my aircraft without a security measure. Usually I use connector caps but sometimes high quality electrical tape or similar. I didn't have the opportunity to check the cables after the incident. The Sea Fury stays at the airfield so I will be able to check it at the next flight day.
