Len

My Feedback: (3)

Hi Guys,
This is a new one on me...I have used Futaba's SBus many times, but just switched to Savox servos for the new Avanti XS as the JR's were not available, and the Futaba's were too large for the servo mounts.

I am using 2 JR 8411SA's on the flaps and the rest are all Savox 1250MG's which are also HV. I power it all with a Fromeco Sahara at 6.1V. I am using Electron gear on an RS-200 controller. The issue is that when I power on the Rx and hence the gear controller, then the rudder and usually the right aileron servo both go into a hunting/oscillating mode. I have control over the servos but they look like old galloping ghost style!!! The gear do not respond at all. If I unplug and replug in the Sbus leads to the affected servos (all on decoders) then everything settles in perfectly. The nose door has a Hitec 225 BB operating it, hence the 6.1V rather than 7.4V, and I doubt the JR 8411's on the flaps would handle the 7.4V either.

Anyone got any ideas? I will be doing some further investigating with servo replacing, maybe take out the gear controller, and higher voltages etc. but I thought if anyone had this before then I'd need not 're-invent the wheel' so to speak...

Thanks in advance,
Len

Bob_B

My Feedback: (11)

Since this was a new build is there a reason you did not use Futaba S-Bus servos or did you have the Savox on hand. I have only done pure S-Bus installs and they have always worked perfectly.

Len

My Feedback: (3)

Hi Bob, I have used JR, Futaba, and Hitec analog and digital servos with the Futaba decoders on many planes with no issue. This was the first time I have tried Savox and I wanted to use them as they have the same output shaft spline (25t) as Futaba. I have used SBus and SBus2 Servos from Futaba as well on installations, so no real reason except possibly the price being significantly lower for more torque and speed in a much better case size to fit the Avanti XS.

The XS called for JR 3401/3421 size servos and well as I'm sure you know they are really hard to get and getting worse as JR Japan shuts down plant after plant with moving and other assorted things. In any event, I have another of these planes at my winter home and I had the same Savox servos sent there too, so I really would like to solve the issue, but I will be testing the worst location on boot with a Futaba servo and disconnecting the other SBus lines to allow for a true testing of the Savox's, hopefully this weekend.

I just really wanted to see if anyone else had run into this yet.
Len

Bob_B

My Feedback: (11)

Ive never used the decoders, I believe each decoder output is control specific?

Len

My Feedback: (3)

Yes they are each programmed to one of the channels 1 to 16 and respond only to that channel. Its the same as an SBus servo. Essentially the addressing is done by the decoder and not inside the servo as an SBus servo would do. BTW I believe the culprit in my scenario above is the Savox servos. I replaced the rudder with a Futaba servo and everything works every time. Not wanting to re-engineer this all, I am ordering Futaba servos at double the cost of course!
Len

Bob_B

My Feedback: (11)

Len will you order SBus servos and remove the decoders?

Len

My Feedback: (3)

At this point it is somewhat difficult NOT to order SBus servos as Futaba's selection gets pretty limited in non SBus digital servos. The answer is yes Bob I have ordered a slew of them S3470SV's as the general servo and S3071HV's for the flaps. It will require some creative installation work for the ailerons, but nothing I can't handle. My concern is the flaps as the 3071 servos while not too expensive are a tad less powerful than the JR DS8411's spec'd by SebArt for the flaps. Though I'd say they will likely be fine. If I replace the 8411's with the 3071's which does allow the removal of the decoders in favor of 'Multi 'Y" connections, then I can move from 6.1V on a regulator to 7.4V on this system, now so the torque spec on the flap servos is then well within boundaries too. Sorry Bob long winded answer, but yes the decoders are only required for non-SBus servos.
Len

Bob_B

My Feedback: (11)

I've always Felt the only way to do SBus is with a true SBus system including the S bus servos. The decoders are rather expensive in my opinion and in your case you found out there was a combatability issue.
by the way I would buy the 4/6 port Hubs and make my own male to male extensions instead of buying the somewhat expensive three-way SBus versions.
Have fun with your model

bidrseed2

My Feedback: (2)

I've had issues with Futaba s-bus decoders and savex servos.

i found whenever I powered up the receiver, ALL the servos would jitter. You would have to cycle the power and then the second time, it would usually behave.
i was using them in a model with 14 of the savox mini servos. I'd initially thought I had dodgy decoders, as I'd bought them when I was in Hong Kong, so I grounded the decoders.

reading this thread has made me think there maybe wasn't anything wrong with them.

Len

My Feedback: (3)

Bob, I agree that the decoders are expensive but to be able to use up all the non serial servos I had was well worth it! I have done over a dozen planes in the SBus and most all had at least one decoder in it and I haven't had any issues with Futaba (of course), JR, or Hitec, or for that matter most of the cheaper Asian servos when used on a decoder.

Birdseed, your experience parallels mine and I believe the servos are definitely the culprits here. I did a whack of testing this weekend with battery power from a 4.8V NiCd, 6V NiMh, LiFePO4 6.6V, and direct (no regulator) LiPo at 7.4V. The only one that "seemed" good was the NiMh 6V. However; when I peaked that battery to 7.2V coming off the charger, it too caused the "jitter". I was beginning to think these servos were allergic to Lithium!!!! Just kidding of course. In my installation I had a decoder in each wing and one in the tail. Oddly enough and supporting the theory that Savox was the culprit, is that NEVER did the JR DS8411's on the flaps EVER jitter at all, at any time! Also only the left aileron Savox servo never jittered. It was always the rudder and one or both elevators as well as sometimes the right aileron. Very odd stuff, but when I replaced the rudder with a Futaba servo, it was rock solid all the time...again supporting that Savox is the culprit. Now I have a few friends using the Savox brand exclusively in their 3D planes and they love them, which is partly why I chose Savox. The servos are great on a servo exerciser and plugged directly into a receiver, but on an SBus decoder they are jittery.

Thanks for sharing your experience...I thought it was just me for a long time...
Len

dbsonic

My Feedback: (3)

I used to see this in other setups even before sbus and it was caused by oxidation of plugs/pins and if I cleaned them with isopropyl it worked fine.

Len

My Feedback: (3)

Worth a try sir, do you just dunk the connectors in isopropyl or do you have to somehow try to get into them?

dbsonic

My Feedback: (3)

Right, with system off, dip the ends of the servo lead exhibiting the odd behavior and then, plug/unplug a few times and then dry with paper towel. you can try to blow them out also. iso dries fairly quick though

Len

My Feedback: (3)

Thanks for the tip db, but it was not the fix for what ails this system. It still jitters like before. I really do like that method of cleaning the connectors though!
New Futaba servos arrive today...
Len

mauryr

Futaba has geniuses at work in their marketing dept.
They make some crappy overpriced decoders that generate some sort of dirty output which causes other brands of servos to jitter and by doing this they drive the sale of more futaba servos.
So by making a bad product they managed not only to sell it, but also to drive the sales of another product, all the while making you think savox are bad
It's pretty sad, because these work perfectly fine when plugged into the receiver...

dbsonic

My Feedback: (3)

I've actually used the decoders on all sorts, never seen any issues. Savox and JR mostly.and some Hitec The only thing I hate about the decoders is they fanout to 3 servos .. an odd number that seems a bit of a gimmick..

Len

My Feedback: (3)

Maury, I too have used the Futaba decoders over many planes with Hitec, JR, Futaba non SBus servos, as well as a plethora of cheaper Asian servos from Bluebird to 'noname' brands, and all were fine until the Savox ones this go around. I may have done something untoward in so far as the SBus protocols are concerned, but it still was ONLY the Savox brand that exhibited these jitters. I tried several brands on the rudder and they all worked except Savox. This issue seems to belong solely to Savox and no one else. Yes all the Savox servos that I have work perfectly fine plugged into an Rx, but obviously that is NOT the impetus of this discussion, neither are the marketing practices of any of the manufacturers named herein. In that light please keep those negative comments to other threads that wish to debate with you. This is not such a thread and therefore I respectfully request you not to post anything that isn't factually related to the discussion at hand or negatively impacting the discussion.

mauryr

I am not debating: I am a pretty loyal futaba customer in fact. I just hate some of their marketing practices, but they clearly work well for them and, in the end, it's just a business so what makes money goes..