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Servo centering myth or reality.

#1
It seems that my servo self-centers when I turn it on. So why in the hell would I need to buy a servo tester for centering purposes? And does it actually center the servo? You see, when I fine-tune the servo with the trim, it centers the servo alright but what else is going on? When using the trim to fine-tune the servo what's really happening is the whole range of motion is being adjusted to one side or the other resulting in more arm travel to one side. So how do you adjust for 1/2 tooth out? You have to mount the servo slightly crooked to get it right. The problem is with the trim, it doesn't account for the overall range of motion, it just moves the whole spectrum to one side or the other. In my case, I get tire rub to the left and when I center the range of motion the trim goes out.
Conclusion: Don't go out and buy a servo tester if all you are looking for is to center your servos. You don't need it.
Resolution: The servo mount should allow for adjustment. A two-piece mount with a locking screw or something to that effect.
Does anyone know if this is available?
Show less
 

FDS

Well-known member
#4
Centering the servo before you put the horn on is always a good idea, there isn’t always room for a bend in control wires and servos are rarely centred when you get them. I often use an omega or Z bend to provide a buffer if the space is there, but centering up before installation is easier.
Decent servo tools have centre, oscillate and dial control options, allowing you to test the control surface after the servo is installed as well.
A $5 servo tool is a lot easier than a complicated adjustable linkage.
 

FDS

Well-known member
#6
I use mine all the time, I don’t always have enough receivers for new planes. Having the servo set up means I can do the ones buried in the fuselage without waiting for a receiver. Even a cheap receiver is $15.
You can use them to set up the ESC as well.
 

LitterBug

Troll Spammer
#7
There are several steps to getting things centered up cleanly. If you buy a servo and the horn is not on it, using a servo tester to center the servo and the horn before you install it in a plane can come in handy. Some models it is impossible to get to the servo after everything is all together, so it is nice to know the servo/horn is adjusted as close to possible to center. It is also a good tool to be able to test a servo and rule out an issue with your TX, RX, flight controller, or any other device in your control system. Depending on your radio, you may have additional control over center and travel in each direction. In effect, you can set the center, and each endpoint independently. This comes in real handy if you have a physical bind in one direction, but not the other. In addition to using a V bend, you can use adjustable end links that either thread on, or have a screw to adjust the rod.
dubro-ezconn-121.jpg


After I get the plane in the air and trim it out, I look at where the control surface is with the sticks "centered", set my radio trim back to centered, and then adjust the linkages so the control surfaces are about where they were when the plane was trimmed out.

Doing all these steps helps prevent the issue where you compensate for a control horn that is not centered or a linkage is bent and you end up running out of travel in one direction after trimming the plane in the radio.

Cheers!
LitterBug
 
#8
I'm not sure I'm following but, if you add a few bends making a 'V' shape along you linkage, you could keep your servo arm in the center and trim by ajusting the pushrod 'length':



View attachment 160123
My steering is a little different in that I have two rods in a push/pull configuration.
So if I shorten one side I would have to lengthen the other. That is difficult with the Z bend.
I should have put a bend in the rod as you have in the picture. Thanks.
PS
I will post a few pictures as soon as I figure out how to do it.
 
#12
There are several steps to getting things centered up cleanly. If you buy a servo and the horn is not on it, using a servo tester to center the servo and the horn before you install it in a plane can come in handy. Some models it is impossible to get to the servo after everything is all together, so it is nice to know the servo/horn is adjusted as close to possible to center. It is also a good tool to be able to test a servo and rule out an issue with your TX, RX, flight controller, or any other device in your control system. Depending on your radio, you may have additional control over center and travel in each direction. In effect, you can set the center, and each endpoint independently. This comes in real handy if you have a physical bind in one direction, but not the other. In addition to using a V bend, you can use adjustable end links that either thread on, or have a screw to adjust the rod.
View attachment 160129

After I get the plane in the air and trim it out, I look at where the control surface is with the sticks "centered", set my radio trim back to centered, and then adjust the linkages so the control surfaces are about where they were when the plane was trimmed out.

Doing all these steps helps prevent the issue where you compensate for a control horn that is not centered or a linkage is bent and you end up running out of travel in one direction after trimming the plane in the radio.

Cheers!
LitterBug

Thank you all for the quick responses. I wish I had done this before I started my project.
I bought something similar to this but I soon found out that the ones I got do not swivel once you tighten them. lol
 

Attachments

LitterBug

Troll Spammer
#13
With a nylock locknut, you could back it off just enough to let it pivot freely.

FYI. Sometimes rotating the servo horn 180 degrees can make a difference on if the horn is centered or not. Especially if the number of teeth on the servo output is an odd number.....
 
Last edited:
#14
A Z or Omega bend in both sides of the steering linkage would be beneficial in that set up. You are putting quite a lot of load through a single servo there without a servo saver to soak up the feedback through the steering. Bends would help with that.
Now I'm showing my inexperience. I have not come across a servo saver.
However, I am already implementing some of yalls suggestions.
 
#15
There are several steps to getting things centered up cleanly. If you buy a servo and the horn is not on it, using a servo tester to center the servo and the horn before you install it in a plane can come in handy. Some models it is impossible to get to the servo after everything is all together, so it is nice to know the servo/horn is adjusted as close to possible to center. It is also a good tool to be able to test a servo and rule out an issue with your TX, RX, flight controller, or any other device in your control system. Depending on your radio, you may have additional control over center and travel in each direction. In effect, you can set the center, and each endpoint independently. This comes in real handy if you have a physical bind in one direction, but not the other. In addition to using a V bend, you can use adjustable end links that either thread on, or have a screw to adjust the rod.
View attachment 160129

After I get the plane in the air and trim it out, I look at where the control surface is with the sticks "centered", set my radio trim back to centered, and then adjust the linkages so the control surfaces are about where they were when the plane was trimmed out.

Doing all these steps helps prevent the issue where you compensate for a control horn that is not centered or a linkage is bent and you end up running out of travel in one direction after trimming the plane in the radio.

Cheers!
LitterBug
I'm currently searching these, Thank you.
 

Figure9

Well-known member
#19
Power your servos via a radio with your transmitter connected, center the trim on your radio, your servos are now centered. Servo centering tools are a waste of money in my opinion.
That’s how I do it too, but setting up a 5g to 13g servo during construction when installing servos, adjusting &/or setting up the control rod to control horn seems less of a hassle with a $10 servo tester. I just wish FT would use smaller print for the very critical power In & servo out connections on their servo tester. I follow up with a transmitter exercise & centering check as the build is nearing completion. The big money waster in my experience is all the sliced up never flown DTFB that I toss in the trash.
 

Hai-Lee

Old and Bold RC PILOT
#20
It seems that my servo self-centers when I turn it on. So why in the hell would I need to buy a servo tester for centering purposes? And does it actually center the servo? You see, when I fine-tune the servo with the trim, it centers the servo alright but what else is going on? When using the trim to fine-tune the servo what's really happening is the whole range of motion is being adjusted to one side or the other resulting in more arm travel to one side. So how do you adjust for 1/2 tooth out? You have to mount the servo slightly crooked to get it right. The problem is with the trim, it doesn't account for the overall range of motion, it just moves the whole spectrum to one side or the other. In my case, I get tire rub to the left and when I center the range of motion the trim goes out.
Conclusion: Don't go out and buy a servo tester if all you are looking for is to center your servos. You don't need it.
Resolution: The servo mount should allow for adjustment. A two-piece mount with a locking screw or something to that effect.
Does anyone know if this is available?
Show less
If you find that the servo arm is out of position by "Half a tooth" the answer is quite simple.
As the output shaft has an odd number of teeth you need to use the servo arm that has 2 arms in one, (one out each side), and fit it to see if it is centred. If not remove it and refit it 180 degrees different where it must be aligned.

Then if you do not have the room for the larger servo arm just trim off the unused arm from the double.

That is one of the reasons you get a selection of servo output arms with every servo.

Have fun!