By continuing to use this site, you agree to our use of cookies. Find out more

SBUS SERVOS

All Topics | Latest Posts

Search for:  in Thread Title in  
LUKE GRICE23/02/2017 19:06:08
12 forum posts

How do SBUS servos work ?

Denis Watkins23/02/2017 19:19:24
4655 forum posts
132 photos

sbus-diagram-lg.jpg

Denis Watkins23/02/2017 19:20:33
4655 forum posts
132 photos

The innovative Futaba S.Bus system lets you unleash your flight system's full potential and cut down on cable clutter at the same time. It uses digital serial data communication technology to transmit control signals between your receiver and servos.

LUKE GRICE23/02/2017 19:33:37
12 forum posts

I know that Denis. But how does it do it. Whats the difference between Sbus and std servos, ?

Denis Watkins23/02/2017 20:12:00
4655 forum posts
132 photos

OK, Luke, All servos are the same and will work with either, its just the board specs and tolerances are tighter on sbus servos.

The work is done by reducing wiring by the hub

And the sbus receiver.

John Privett23/02/2017 21:17:29
avatar
6106 forum posts
243 photos

I think you've missed the point Denis. SBUS servos are very different. All SBUS servos on an installation receive all the data for every channel, but are programmed to only respond to the channel that you select. So you program the throttle servo to respond to the throttle channel, the elevator servo to respond to the elevator channel etc. etc. The hubs are only a means of splitting the wiring to multiple servos. Conventional servos can also be used, but they need a decoder to read the SBUS signal and output on separate leads for the servos.

Have a look at the following videos for more.

Denis Watkins23/02/2017 21:36:50
4655 forum posts
132 photos

No expert was coming forth John

And I am so glad you did to clarify SBus

Thanks

John Privett23/02/2017 21:57:24
avatar
6106 forum posts
243 photos

No problem Denis! Funnily enough I'd been looking at the FrSky SBUS offerings immediately before coming onto here this evening.

ben goodfellow 124/02/2017 04:39:58
avatar
1069 forum posts
41 photos

the thing that dosent thrill me,,, say them 6 servos at the back are 7950 .777s ore 8931s which can pull 7 amps each .......42 amps through that from batt !!!!! ,, no thanks

Allan Bennett24/02/2017 08:18:53
1775 forum posts
55 photos

I'm glad I read this. I always thought that the hubs did the magic decoding, so that you can then use any servo. Since they don't, I have to wonder why not: Is it to lock you in to Futaba's special servos? Are the hubs simply dumb Y-leads?

Frank Skilbeck24/02/2017 09:33:00
avatar
4867 forum posts
107 photos

Allan, you can also get a decoder hub which allows you to use conventional servos, so you could have a mix of regular and SBus servos in the model.

Also Ben you could have multiple batteries around the system, if you are going to have a system that pulls 42amps from a single power source you'd need to make sure it has a good distribution system or the receiver is designed for it.

Bob Cotsford24/02/2017 10:12:43
avatar
8840 forum posts
496 photos
Posted by Frank Skilbeck on 24/02/2017 09:33:00:

Allan, you can also get a decoder hub which allows you to use conventional servos, so you could have a mix of regular and SBus servos in the model.

Also Ben you could have multiple batteries around the system, if you are going to have a system that pulls 42amps from a single power source you'd need to make sure it has a good distribution system or the receiver is designed for it.

Be careful there - some (maybe most?) decoders such as the FrSky and XPS ones use the Sbus frame rate coming out of the receiver, in FrSky's case 15ms. This will cook a standard analogue servo so digital servos must be used. One useful feature of the decoders I've used is that you can program the output to respond to any available channel eg a 4 channel decoder can be set to output channels 1, 5, 7 and 16 or whatever you need.

Also Allan, decoders and sbus servos can be linked with plain old Y leads.  The only hubs that I've used are actually decoders.

Ben - the FrSky 4 output decoders are rated at iirc 6A while I think the XPS has a higher rating as it can take it's own power supply, but even then the standard servo connectors aren't rated for the 7A per servo that you are quoting. You are talking VERY specialist applications there which would need very specific and well designed power distributions systems.

There are variations on the sbus theme, Futaba JR etc which are not compatible with each other.

Edited By Bob Cotsford on 24/02/2017 10:15:41

Tim Ballinger05/08/2018 08:43:01
avatar
802 forum posts
290 photos

Is it still true that the FrSky sbus decoder has too high a frame rate for analogue servos? The current advertising says they work with standard analogue.

This months RCM&E article is not quite so bold and suggests only standard digital. Where does the truth lie?

Tim

Tim Ballinger05/08/2018 08:56:56
avatar
802 forum posts
290 photos

Reading further into the manual I find..

he decoder’s output PWM frequency is automatically match with the input CPPM/SBUS signal frequency, make sure the proper servo is connected. Do NOT use conventional servo with SBUS High Speed mode and/or CPPM mode when frame length is shorter than 14ms.There is the danger of erroneous operation or damage.

So my question now changes to can you set the Sbus frequency/speed in any of the FrSky rxrs , in particular the rx8xr pro. ?

Tim

Bob Cotsford05/08/2018 09:41:22
avatar
8840 forum posts
496 photos

You can certainly set a frame rate on the transmitter if you are using OpenTX 2.2.1 onwards in D16 mode. I don't have a scope to check the output so I'm just going by the bind options presented in OpenTX.

I do know that earlier implementations used something like a 9ms frame (source - Jim Drew XP Systems commenting on the X10+ thread on RCGroups) and would cook analogue servos as I found out the hard way.

Biggles' Elder Brother - Moderator05/08/2018 09:52:58
avatar
Moderator
15748 forum posts
1460 photos

Tim,

I wrote the article in this month's mag. I have used this system in three models now, all warbirds where I had a lot stuff coming out of the wings. In one, the first, I used analogue servos. I got away with this, for a short time, then one by one I started getting servo failures - fortunately none of them led to serious problems, two aileron servos and one flap servo.

I then read about the frame rate issues, since then I have simply stuck to digital servos in these applications. The servos I am using in the Sea Fury are, in my view, a very good servo for a good price. They have high torque output and they are quite fast. Since going over to digitals such as these I have had absolutely no problems whatsoever. Being a life long member of the 'if its working leave it alone club' I stick with digitals! Other solutions may be possible via changing frame rates etc., but as I have no experience of them I can't personally recommend them and I certainly wouldn't down in print recommending a solution that I have had a failure with in the past, although as has been pointed out the situation may have subsequently changed.

BEB

Edited By Biggles' Elder Brother - Moderator on 05/08/2018 09:55:06

Tim Ballinger05/08/2018 10:26:05
avatar
802 forum posts
290 photos

Thanks both. As you might have inferred I am thinking of changing to FrSky and was also looking to tidy my wing wiring which has just far too many plugs for comfort.

I was half thinking of changing the wing servos to digital to avoid the issue, much as you describe BEB then I remember the retract servos are standard HK units which would also need replacing if I really wanted to go down to single cable. It was then I started looking to see if the frame rate could be kept at the high or normal setting. What is unclear to me is does the setting change fix the Sbus output or just the analogue outputs. Any thoughts Bob.

Tim

Btw BEB what digital servos were you recommending?

Tim Ballinger05/08/2018 10:28:21
avatar
802 forum posts
290 photos

Forget the last question I see the answer in the mag: savoy.

Tim

Former Member05/08/2018 11:09:51
8090 forum posts

[This posting has been removed]

Tim Ballinger05/08/2018 11:20:15
avatar
802 forum posts
290 photos

Guess savoy is a cabbage ! Should have been savox. 

Not sure it’s excessively complex Percy, but you do need to get it right.

Tim

Edited By Tim Ballinger on 05/08/2018 11:20:36

All Topics | Latest Posts

Please login to post a reply.

Support Our Partners
Subscribe now
CML
Slec
electricwingman 2017
Sussex Model Centre
Sarik
Advertise With Us
Latest "For Sale" Ads
NEW POLL - has the pandemic altered your event safety perceptions?
Q: Has the covid pandemic deterred you from attending shows and events in 2021?

 No, I'll be attending just as many as I usually do
 No, but I'll choose my event with greater care
 Yes, I'll attend fewer events going forward
 Yes, I wont attend any where previously I have

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E!