LUKE GRICE Posted February 23, 2017 Share Posted February 23, 2017 How do SBUS servos work ? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 23, 2017 Share Posted February 23, 2017 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 23, 2017 Share Posted February 23, 2017 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. Quote Link to comment Share on other sites More sharing options...
LUKE GRICE Posted February 23, 2017 Author Share Posted February 23, 2017 I know that Denis. But how does it do it. Whats the difference between Sbus and std servos, ? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 23, 2017 Share Posted February 23, 2017 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. Quote Link to comment Share on other sites More sharing options...
John Privett Posted February 23, 2017 Share Posted February 23, 2017 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. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted February 23, 2017 Share Posted February 23, 2017 No expert was coming forth John And I am so glad you did to clarify SBus Thanks Quote Link to comment Share on other sites More sharing options...
John Privett Posted February 23, 2017 Share Posted February 23, 2017 No problem Denis! Funnily enough I'd been looking at the FrSky SBUS offerings immediately before coming onto here this evening. Quote Link to comment Share on other sites More sharing options...
ben goodfellow 1 Posted February 24, 2017 Share Posted February 24, 2017 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 Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted February 24, 2017 Share Posted February 24, 2017 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? Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted February 24, 2017 Share Posted February 24, 2017 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. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted February 24, 2017 Share Posted February 24, 2017 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 Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 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 Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 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 Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted August 5, 2018 Share Posted August 5, 2018 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. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted August 5, 2018 Share Posted August 5, 2018 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 Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 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? Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 Forget the last question I see the answer in the mag: savoy. Tim Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 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 Quote Link to comment Share on other sites More sharing options...
Mike Blandford Posted August 5, 2018 Share Posted August 5, 2018 I have an Arduino project that is a SBUS decoder here: **LINK** By default the output rate is 18mS (for analog servos). There is an option to switch to 9mS. Mike Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted August 5, 2018 Share Posted August 5, 2018 Posted by Percy Verance on 05/08/2018 11:09:51: Wow. Looks massively over-complicated. I'll stick to keeping it simple I think...... Actually Percy that diagram at the top of page one is very misleading. I've found that using the FrSky decoders for the sake of one extra component I get a four times reduction in the number of wires roaming around the model and having to be connected correctly at assembly time. So my experience is: used where it will benefit, coming out of the wings for example; and sticking with the conventional set up for those servos in easy reach that can be perminatly connected to the Rx (throttle, elevator, rudder etc. for there is no rule that says it has to be 100% one or the other youcan pick 'n' mix in the same model), far from adding complexity it brings a welcome reduction in complexity and general wire clutter. BEB Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 Arduino projects are new to me Mike. I am presuming one has to actually make up that board as specified and coded , in this case by yourself. While it sounds to have the exact functionality required to decode an run analogue servos from an Sbus I am definitely not skilled enough with a soldering iron to take that on as a project. Thanks for the thought though. Tim Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted August 5, 2018 Share Posted August 5, 2018 I also assume BEB that de facto it allows you to use 8 analogue plus 4 or more from the Sbus. Not sure I can think of why I would need that many channels but I am sure someone can! Tim Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted August 5, 2018 Share Posted August 5, 2018 Yes Tim and any other combination you find helpful. I have used new digitals throughout as its an example build for the mag, but I could have put analogues I happen to have in stock on the elevator and rudder if I wanted as they are connected directly to the Rx and not via the SBus. BEB PS I should perhaps add that you do of course have to use the FrSky channel selector widget to set the SBus channels to beyond 8, so as to avoid any potentional conflict with actual Rx connections such as those discussed above. Edited By Biggles' Elder Brother - Moderator on 05/08/2018 17:05:28 Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted August 5, 2018 Share Posted August 5, 2018 I can vouch for Mike's Arduino S.Bus decoders. Here's one I made earlier - just as a test. If you search hard enough at Bangood, there are a number of types available. These work well. Giving either channels 1-8 or 9-16 on the servo ports. These ones have all 16 servo ports available. The 16 channel one shown can be used out of the box. Or there's downloadable software with many settings available, including frame rate. (Although you would need a cheap USB-FTDI adapter and jumpers to connect the two). Finally if you need a good amount of power handling for higher powered servos, then check out the FrSky Redundancy BUS 10 and Redundancu BUS 20. Both have two, high power battery inputs. They will take an S.Bus signal from two separate receivers and choose the best signal and they have 16 servo ports. Edited By Chris Bott - Moderator on 05/08/2018 20:13:52 Quote Link to comment Share on other sites More sharing options...
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