I am new to FrSky and just got a X20S need help with servo centering.....

[crgonzalez08]

Hello, I am totally new to Ethos and FrSky, coming from JR systems.
I am trying to set up a big scale gas airplane with 4 servos on the ailerons. I need to match the 2 servos o each aileron, so my question is, How do I go about centering the servos and making sure they both travel the same way. What I have done so far is create a free mix per servo and on this mix i have offset the curve to move the center of the servo, Am I right by doing this?
The manual says not to use sub-trim for centering servos because this will affect the resolution on the servo.
If you guys have any direction or ideas on how to do this, i will appreciate any help.
Thank you

 

[Konrad]

You got it. I do this with curves and an amp meter. Use the center point of the curve to match the aileons to the profile of the wing. And then use the other 3 points on each side of the center point to match the other servo. I find there is a lot of help following the set up in Mike Shellim's templets for how to set up a calibration flight mode.

As I'm sure you know you don't want the servos on the same surface fighting each other. this is why I use an amp meter to make sure the servos are calibrated to follow each other. If there is a misalignment you will see it in the amp draw. it is better to find this on the bench rather than burn out an output transistor in the air.

How is this matching of servo motion done with the JR?

 

[Raymond Gaskins]

Being an old time user with JR, the JR matchbox device was used to adjust multiple servos to work in tandem with the same control surface. Then, the newer transmitters offered servo adjustments in the Xbus protocol for the NX line of servos through either the xbus menu or with a separate digital servo device. Non xbus digital servos could be programmed the same way using a conversion harness between the servo and receiver or bus expansion device. I always used an ammeter to dial the servos in. Hope this helps Konrad.
Raymond

 

[crgonzalez08]

I thought I was doing this right, but if I set a offset curve it takes away from one end of the servo, am I doing something wrong?
Another thing is, how do I add or take off the servo travel?
The weights on the servo channels are doing nothing when i change the value.
Thank you for your help

 

[HENNY]

How much offset are you applying. There is a limited amount of servo physical travel so offset pushes the travel left or right. This is true for all radios. Are you sure you have centered your servo horn. Center is at 1500. So check this first you may need to move the servo horn by removing it to find true servo position center. I always check this with a servo tester.

In the FRsky world "Weight" is the amount of servo travel 100 or -100. So 50 would be half travel and -50 will be half travel in the opposite direction. So if you were mixing several functions into a given channel like Elevons you would mix 50% Ail and 50% Ele, this would then add up to 100% servo travel. To limit the servo travel, say due to binding at the travel limit is done in the output menu. This enables independent mixing in the mix menu and independent centering and servo travel in the output menu.

 

[Konrad]

The issue I have with multiple servos driving one surface is that if the digital servos are not matched exactly they will fight each other and drain the power source or burn out the servo output stage. With curves the end point, centers and with 5 of more points even the middle shape of the throws can be matched to allow the servos to follow each other.

I leave the output menu alone and use the servo curve in the mixer to control the profile of each servo response.

 

[ORRich]

This is an Ethos channel but I think the same applies to OpenTx - my new DLG has the surfaces completely off - I want to set up the CAL mode per Shellim's tutorial, but it seems that I first need to get the servos close to their position by physical taking off the horn and placing it nearish the center? Currently, the ailerons are about 15mm in the down position when everything is centered - I presume CAL mode is not used to center when they are that off, is that correct? The reason I ask is that the Hawk DLG cockpit is very tightly packed and not sure how to remove the servos and re-center the horns

 

[Hill Hobbit]

Hi Rich, I don’t know if you’re using Mike’s DLG template, but if you are (even if not) pop him a pm and he’ll give you all the help you need. He’s a great guy!
Cheers
Jonty

 

[Raymond Gaskins]

This is an Ethos channel but I think the same applies to OpenTx - my new DLG has the surfaces completely off - I want to set up the CAL mode per Shellim's tutorial, but it seems that I first need to get the servos close to their position by physical taking off the horn and placing it nearish the center? Currently, the ailerons are about 15mm in the down position when everything is centered - I presume CAL mode is not used to center when they are that off, is that correct? The reason I ask is that the Hawk DLG cockpit is very tightly packed and not sure how to remove the servos and re-center the horns

Hi Rich,
I have several Hawks and went through the same struggles you are going through with servo setup in such a tight space. So far, I have used OTx, but have a Tandem 20s with Ethos that I am learning to program but have not actually set up in a DLG.
I found the servos easy to pop loose by using a thin but sturdy plastic prybar of the type used to open smart phones and computers. I then centered the servos with a servo tester and recentered the servo arm.
Then, I wrapped each servo in large plastic heatshrink and reglued them in place.
This worked well and if I have to replace a servo in the future, it’s just a matter of prying the glue from the heatshrink without damaging the servo.
Hope this helps. If you can set up a Hawk, everything else will seem cavernous in comparison. I used a 4 channel FrSky receiver behind the servos and a single cell lipo in front and tungsten putty added in front of the battery to achieve an optimal cg.
Best,
Raymond Gaskins

 

[ORRich]

Hi Rich,
I have several Hawks and went through the same struggles you are going through with servo setup in such a tight space. So far, I have used OTx, but have a Tandem 20s with Ethos that I am learning to program but have not actually set up in a DLG.
I found the servos easy to pop loose by using a thin but sturdy plastic prybar of the type used to open smart phones and computers. I then centered the servos with a servo tester and recentered the servo arm.
Then, I wrapped each servo in large plastic heatshrink and reglued them in place.
This worked well and if I have to replace a servo in the future, it’s just a matter of prying the glue from the heatshrink without damaging the servo.
Hope this helps. If you can set up a Hawk, everything else will seem cavernous in comparison. I used a 4 channel FrSky receiver behind the servos and a single cell lipo in front and tungsten putty added in front of the battery to achieve an optimal cg.
Best,
Raymond Gaskins

Thanks Ray - that info is extremely helpful - yes my Blezncyk Elf feels like a 4m scale in comparison - lol - I will try and 'cheat' with the CAL mode first as there seems to be a generous amount of servo travel - I only need a few mm for camber - if I can't swing it, then I'll do the more invasive servo removal and replace with heatshrink -

 

[gnichola]

If you are not using something like Mike's template and just want to do a basic servo match type thing, I would start by getting 0 as close as possible mechanically, then go to the Outputs section and use PPM Center to adjust one servo or the other. This differs from using a mix or the Center/Subtrim setting in that it moves the entire servo range one way or the other, leaving equal movement on either side. Subtrim just moves the center and leaves the endpoints the same giving you more travel on one side and less on the other.

 

[ORRich]

If you are not using something like Mike's template and just want to do a basic servo match type thing, I would start by getting 0 as close as possible mechanically, then go to the Outputs section and use PPM Center to adjust one servo or the other. This differs from using a mix or the Center/Subtrim setting in that it moves the entire servo range one way or the other, leaving equal movement on either side. Subtrim just moves the center and leaves the endpoints the same giving you more travel on one side and less on the other.

Thanks Gnichola. I re-glued the servos and now will play with learning how to program the CAL mode. If not, your suggestion is welcome and may try that.