Hi Guys!

My three KST DS725MG cyclic servos makes a lot of noise, vibrations and heat up at in the zero position with Spirit Pro. In other positions the servo works fine. The tail servo BLS805X on this same FBL works great in any position.

The servo frequency is correct 1520μs/333Hz and even when it is reduced to 150hz the noise does not disappear. If you reduce the BEC voltage from 8.4V to 6V, the noise disappears a little but still remains.

When I connect another servo (Align DS525M) with the same frequency it works absolutely fine. When I connect these KST servos to another FBL Spirit GT the problem remains. That is the problem is precisely in the compatibility of DS725MG with Spirit.

Technically the servos are fully functional. Inspection of the servo gearbox did not reveal any problems. Probably the problem is in the FBL settings. I am attaching the file with the settings and hoping for your help.

Video with sound:

https://www.youtube.com/watch?v=Bvj9sEmHfHk

Some old KST, RJX and BK servos made in the same company had incompatibility issues with some FBLs. You can try lowering BEC voltage.

_________________
Spirit System developer

This servo is not old, it is now sold on the KST website and in many stores. How can I know about these compatibility issues before buy? KST DS725MG is on the Spirit servo list, I can't even predict such a problem.

I reduce the BEC voltage from 8.4V to 6V but the noise still remains.

same problem as my align bl815h
changed the servos no problem.
Unfortunately there are 10,000 servo controls spirit can't try them all.
but it's not just with spirit even if you connect the servos on other flybarless.
But if you connect the servos with the receiver is all ok.
I saw that servo controls they use other people with spirit gt and I took the same model.

do research on the internet and if you find a model where no one has problems you buy that model.
But he is not guilty spirit.
The problem it's from the servants' brand.
Align bl815h it costs a lot more but they have that problem.
other servo controls more cheap everything is ok.

Thank you for your comment, it's very sad to hear about such uncertainty. I have never seen such a problem before.

Unfortunately it was only guess, I am not sure why you can see such problem.
Very likely the same servo works well for others. The issue could be even caused by receiver placement very close to the servos.

In any case you can send me your settings file. The problem could be also in the radio itself. Could you verify channel monitor in your radio in the middle position? Does the value remains still?

For example we never seen any issue with Align, Savox, MKS, Futaba servos. If there is incompatibility issue then it could be only with some batch of the servos. There is nothing different for Spirit than for other FBL units.

_________________
Spirit System developer

I did some tests and only at 5v the vibrations disappear completely. I think this is a very low voltage for an 8.4v servo.

They worked fine with VBar.
I use two Spektrum satellites, they are far from the servos. I tried to turn them off without result.
The monitor readings are stable in the middle position.
If I order new KST BLS815 how can I make sure they don't have the same problem?
Please check it out

We know that just three manufacturers are not doing a proper testing - KST, RJX, BK. All these manufacturers had issues with various FBL units including Spirit with certain models/batches. There is chance they are testing for example with only certain FBL units where it could work correctly.
Unfortunately you can never know which model it is and in theory strange things could happen with any servo. But as far as I can tell, only these 3 were problematic within servos produced in last 20 years.
Additionally these are coming from one Chinese company, labelled with their brand or custom enclosure. In other words I recommend to buy servos from other brands. This is very problematic area, because the only thing that is causing such incompatibility issues are because of too high resistance (resistor) in the signal path, making incoming signal too weak. FBL controllers with circuits protected for overvoltage and reverse polarity could be affected more likely, because there resistance is also higher.
From your description it really look like compatibility issue, but we know that this servo is working well at least for some pilots and was tested with Spirit many times.
Sadly there is nothing we could do about this, because resistance in Spirit units are strictly controlled with only 0,1% tolerance deviation that exclude possible error at FBL side. But it is quite easy for the servo manufacturer to properly test and use correct resistance to make it compatible with all units. For example Spirit units are in the market for much longer time than all these brands.

We could buy the same servos and check compatibility it for you at least to confirm with the recent batch.

_________________
Spirit System developer

Thank you for your reply. I like the KST servos and their other models work well with the Spirit. I wrote to KST support but due to the Chinese New Year they are responding with a delay.

To close this thread please check my settings file in the post above to check if it was an error on my part.