• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Flysky FS-I6x transmitter with 270 degree servos question

#1
I am looking to purchase a Flysky FS-I6x transmitter for a project that I am working on. The issue I keep running into is how I am going to control 4 separate servos with 4 switches. I need to turn a servo about 120/130 degrees from starting position and return to start. From my understanding that even though servos are rated for a certain degree, they won't actually turn that far unless you have the correct PPM (or PWM I forget which). If I understand correctly, servos center at 1500 and from what I have seen (but not confirmed) the pulse on the transmitters go from 1500 - 1000 or 1500 - 2000. Am I correct on this, or can the settings be changed to get a higher or lower pulse?

So the 2 solutions I am looking at are as follows.

1. Get a 180 or 270 degree servo and set switch on Flysky to be always pulse at 1000 until switch is flipped and raise the number to 2000, hoping that this will be enough distance to get my 130 degree rotation. Is this possible?

2. Or get a 270 degree servo and try and get the transmitter to pulse at 2500 to get the full range of the servo to get my 130 degree turn from starting position

I am trying to figure this all out before I make my purchases. Thank you for your time.
 

DamoRC

Well-known member
Mentor
#2
Servos center at 1500 microsecond (us) PWM. Then their full range runs from 1000 to 2000 us.

If you buy a 180 degree servo then my assumption will be that it will swing the full 180 degrees as you provide it 1000 to 2000 inputs, that is to say, the angular sweep of the servo is handled by the electronics on the servo using an assumed standard 1000 -2000 us range.

So all you should need to do is have the starting position on your switch provide 1000 us and the second position on your switch provide 1000 + (130 / 180 * 1000) ms, which is 1722 us

For the 270 servo, just substitute 270 for 180 in the above equation.

You might be able to get 130 degrees sweep by extending the endpoints on the switch outside the standard 1000 - 2000 us range (say from approx 800 to 2200)

There are also a number of hacks you can do with regular servos to increase their sweep range.

EDIT: corrected units from milliseconds to microseconds.

DamoRC
 
Last edited:

DamoRC

Well-known member
Mentor
#4
When watching Youtube videos, servos look like they are only moving in the 90 to 100 degree total range. This is why I am confused.
Yep - that's the standard range but there is always wiggle room at either end. Not sure if it will get you all the way to 130 degrees. Also, one thing to watch for with a standard servo is that there is typically a mechanical stop built into the cover to stop the servo arm travelling too far. This also protects the pot which reads the position of the servo arm from being over extended.

DamoRC
 

DamoRC

Well-known member
Mentor
#5
Did a quick and dirty experiment with one of my $2.50 9g analog servo from HK.
Mechanical limit is approx +/- 90 degrees from center (so its mechanically capable of 180 degree sweep)
Connected to receiver on aileron channel, max sweep is 90 degrees (+/- 45 degrees from center)
Increased travel adjust endpoints on the transmitter to 125%, max sweep was 115 degrees.
Connected to arduino using the "Knob" example under the Servos example code and it can sweep the full 180 degrees.

So as long as your radio will let you increase the endpoints or set the PWM at the correct values, you should be able to cover the 130 degree sweep easily enough with a regular servo. Instead of using the approach described above for the 180 and 270 degree servo, I would set your switch values for a regular servo to be 778us and 2222us (although you might want to check that math)

DamoRC
 
#6
Thank you for going the extra mile and doing the experiment. This issue has perplexed me for a few days and that is why I posted the question. I think some hands on experimentation is the best way to go.
 

pressalltheknobs

Posted a thousand or more times
#7
Generally depending RX TXS do not necessarily send the full 1000us-2000us even when using extended limits. Also, while close, 1500us is not necessarily the center. It depends on the brand. You can usually adjust the center using subtrim. Some radios have additional low level setting for PWM center. You generally can't adjust the range outside of the maximum the TX allows except by setting extended limits which typically extends the range from +-100% to +125%. TXs generally let you set a lower limit than the standard max (or extended max if used)

I haven't played with a FlySky i6x but I suspect it is the same in this respect as the FlySky i6. That TX does have extended servo range which I think is +-125% of standard...don't have one here to check and its not in the doc. I don't know what uS range it puts out for either standard or extended but personally I would not count on any particular RC TX sending the range you want unless someone has done the experiment.

The HK HXT900 9g servo I have will turn about 200degrees mechanically. With a FrSky X9D+ with standard channel range the TX says it is sending 1033us to 2012us and the servo move about 90 degrees full sweep.
Setting extended limits (max +- 150%) the tx says it is sends 732us to 2268us and the servo moves about 130 degrees full sweep.
FrSky is noted for have a higher pwm range than most other TX brands.

It does seem likely that "wide angle" servos like this will move through more degrees for the same uS sweep but it could be that they just accept a broader uS range. I don't have one to try.

If you really need the full 180 degrees you are probably better off using an arduino or similar
 
#8
I have considered going the arduino route but it itself brings up more challenges. For this project, I already have about $450.00 sitting in my amazon cart ready to be ordered. This is a bit more expensive than I originally thought. (RC builds can be expensive when starting from scratch and have a specific concept in mind)

I believe that I would have the technical skills to figure out the arduino and make it work with my project but this adds to the cost and it is one more point of failure in the overall scheme. I have looked at stepper motors and low turn motors as a backup but figured the servo would work easier and be cheaper straight out of the box if I can solve this issue.

I think that flysky is max +-125% from what I've seen so far. So the hope is that a 270 degree servo has a 100+ degree throw with standard settings. Then using +-125 on the controller should get me close to 150 degrees of total throw. If I only get 90 degrees with standard setting and if the math stays consistent, then I should still get to my desired 130 degree total throw. Cutting it close though.

Does anyone have a 270 degree servo to confirm?
 

DamoRC

Well-known member
Mentor
#9
Generally depending RX TXS do not necessarily send the full 1000us-2000us even when using extended limits. Also, while close, 1500us is not necessarily the center. It depends on the brand. You can usually adjust the center using subtrim. Some radios have additional low level setting for PWM center. You generally can't adjust the range outside of the maximum the TX allows except by setting extended limits which typically extends the range from +-100% to +125%. TXs generally let you set a lower limit than the standard max (or extended max if used)

I haven't played with a FlySky i6x but I suspect it is the same in this respect as the FlySky i6. That TX does have extended servo range which I think is +-125% of standard...don't have one here to check and its not in the doc. I don't know what uS range it puts out for either standard or extended but personally I would not count on any particular RC TX sending the range you want unless someone has done the experiment.

The HK HXT900 9g servo I have will turn about 200degrees mechanically. With a FrSky X9D+ with standard channel range the TX says it is sending 1033us to 2012us and the servo move about 90 degrees full sweep.
Setting extended limits (max +- 150%) the tx says it is sends 732us to 2268us and the servo moves about 130 degrees full sweep.
FrSky is noted for have a higher pwm range than most other TX brands.

It does seem likely that "wide angle" servos like this will move through more degrees for the same uS sweep but it could be that they just accept a broader uS range. I don't have one to try.

If you really need the full 180 degrees you are probably better off using an arduino or similar
Good info. The 270 servo you linked to takes a 500 to 2500 us range. Assuming this equates to the full 270 sweep, then a standard Tx with a 1000 us sweep will get you 135 degrees even without endpoint adjustment.

DamoRC