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What is the value of S-Bus as there are so few S-bus servos?

Konrad

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A few years ago I noticed that there was an up tick of new servos coming on the market. I recall FrSky had some S-bus servos in the 9gram class. I'm wondering it there is an inherent problem with S-Bus as I haven't seen any new servos coming on the market that is S-Bus compliant. In fact now that Fr Sky doesn't market servos there are even less than yesterday. Are the Futaba S-Bus, S-Bus 2 servos compatible with the Fr-Sky S-bus receiver?

I have noticed that Aloft sells an add on decoder that allows one to convert PWM servos to S-Bus. $10 dollars makes it hard to justify converting some of the economy servos. But sometimes it might make a few set ups easier.
https://alofthobbies.com/frsky-sd1-sbus-converter.html
 
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Wayne

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Yes, I saw a need for such a converter and asked FrSky to develop this product. My thought was simply allowing any digital servo to be used on an S-bus line. Rather than waiting for decent S-bus servos to be introduced, with this adapter you can use your favorite servo today.
 

Konrad

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Wayne, Thank you!

It would be nice if servo OEM like KST would make servos that were native S-bus.
I assume that analog servos are at risk as a result of the refresh rate?

Are we stuck with proprietary S-Bus codes or has the industry settled on a standard?

Are we still in the chicken or the egg part of the development curve ( S-Bus RXs and S-Bus servos)?
 

Konrad

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These days flight controllers like sbus.... beta flight, iNave, Clean Flight family
Flight controllers? Aren't those known as thumbs? ;)


I assume these are the gyros used to control the asymmetrical thrust multi-rotor craft (AKA Drones). Don't these craft also use servos to drive the camera panning platforms?

I have to ask if it is these S-Bus protocols that differentiates the aircraft (fixed wing) ESC from the multi rotor ESC?

http://www.castlecreations.com/en/clearance-items/multirotor-35-quadpack-010-0125-00

http://www.castlecreations.com/en/multirotor-35-esc-010-0138-00

http://www.castlecreations.com/en/talon-1/talon-35-esc-010-0122-00
 
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Scott Page

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I don't think there is a critical mass of hobbyists WANTING Sbus servos. To be brutally honest and pessimistic -- I don't think there will be a critical mass because setting up Sbus > servos requires two more neurons than the PWM. The only place I've seen Sbus being used (much) is in flight controllers in helis and "drones".I believe this is because it's easy to connect one cable between the Rx and FC. People seem intimidated to use Sbus with servos, perhaps just by the unfamiliarity; or perhaps because they don't see an advantage for their application.
 

Konrad

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I fear you are right. I wonder what the sale numbers look like for Futaba's S-Bus servos.

I'm in the process of soldering up sets of wiring harnesses for my 90mm to 120 mm jet and 3 meter plus gliders. Having a serial bus would save a lot of work and weight only needing to run 3 wires. Unfortunately the decoder offered by Aloft/FrSky doesn't cut down on the work but it sure helps with the weight and makes for a much neater installation.
 
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RCdiy

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One reason I'd not use sbus servos is that you have to assign a ch number to the servo... lets say I servos sitting on the bench. A pwm servo I just wire up and what I see is what I get... for sbus I have to pull out the channel changer and check each servo and maybe even label each servo so I know its number... adds more overhead than it solves (if it solves anything at all)...
A bus topology is useful is one has a cluster of servos at a distance so run one cable but even then it now has to be a thick cable to handle power draw by multiple servos at a distance; as distance increases and number of servos increases the wire thickness may need to increase as well...
 

Konrad

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Yes, to the power demands. But the power demands are the same for any given number of servos, be them S-bus or PWM. But as these are digital servo the power needs are pulsed so the actual wire weight (mass) can be much less than the total sum of the individual servo power leads. Now I use a common bus architecture for powering my remote (long distance) servos to take advantage of this (pulsed) even without S-Bus. S-Bus saves in the signal wire weight and associated connector pins.

Even with PWM I still need to keep track of which servo is which when making up wiring harnesses and plugging which servo in which Rx port. With S-Bus this organizational issue really is much simpler.
 

RCdiy

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Are you sure the pulse power demand is perfectly interleaved?
The proof is in the actual trying and if it works, it works :)
 

Konrad

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Are you sure the pulse power demand is perfectly interleaved?
The proof is in the actual trying and if it works, it works :)
Yes, it works fine at least up to 6 servos from any bus. (I have years of experience with this, but mainly use 4 servo per bus, Heck our receiver use a common bus to drive 8 or more servos.) We are taking about the voltage drop (Wire impedance) as a function of current draw. AC (pulsed) voltage theory is a bit different from straight DC.

Your concern with perfectly interleaved pulses has to do with power supply being able to supply the power for the milliseconds that the pluses interact (add up). This is a concern regardless of the power bus architecture.

Anybody have any input as to the S-Bus communication protocol between various OEMs and brands. I'm happy that we have some commonality with PWM. I'm just concerned that with software so many OEMs are more concerned with protecting their brand, that concerns for the end user is often kept out of the equation.
 
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RCdiy

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I would guess SBUS protocol is now fixed given the years of equipment already out there. For either FrSKY or Futaba to tweak it would be asking for trouble (not that it may stop them). SBUS is inverted standard UART.

FrSKY and BetaFlight are working on a new protocol FPort to carry servo and tememetry on the same wire for flight controllers.
 

Konrad

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This is good news, I think.

I had figured out that the transmission was inverted UART. What I’m not clear on is if the decoded data is universally recognized by the servo. That is can I use a Futaba* S-Bus servo with a Fr-Sky RX? Or the reverse can I use a Fr-Sky servo with a Futaba RX?

Or put another way do all the OEMs use the same data bits to define servo location and position?

https://en.wikipedia.org/wiki/Universal_asynchronous_receiver-transmitter
https://www.futabarc.com/servos/sbus.html
https://alofthobbies.com/radio/servos/frsky-servos.html



*Not that Futaba is the preferred OEM in the USA, with their distribution network in disarray.
 

Wayne

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Interesting about the Fport project.

S-bus is a standard that Futaba defined and shared with everyone many years ago. Frsky follows that standard as should everyone else. I honestly have not heard of any S-bus complaints from customers other than some non-standard flight controllers a while back. That was an issue with the flight controllers not being standardized.

With this said, I was recently excited about an S-bus based hub and some flight controllers I had found from DualSky. Well, it turns out that the FrSky S-bus does not work with these devices. I am trying to get DualSky to fix the issues.

As far as flight controllers go, they can be used for fixed wing applications also. :) Very few people do..

S-bus is really great for removing wire clutter and making wiring much easier. I think you add one type of complexity in exchange for easier wiring. Does that make sense? I personally rather like S-Bus for servo applications, but maybe that is because I understand it more than the average pilot? I think it works very well with OpenTX.

Another advantage is that it is a digital signal that it able to sort out noise, this is a very big improvement over running PWM with long wire runs. I have had my share of PWM lines that pick up radio noise on the wires and the servo then tries to act on them. I believe this is not much concern with S-Bus. (Obviously lots of radio noise would wipe out any communications, but atleast the servo not be doing random things.)
 

Konrad

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Great!! Thank you, I must be some kind of fool (poor Google-fu,) as I never was able to find that concise an answer!

While I may have added some complexity (soldering in the decoder) it really does make the rest of the set up easier!

And yes, I love the digital filtering of noise, so common with those long servo leads!
 
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Marty McFly

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I used S.Bus on Mulitplex FunCub where wing have four regular "budget minded" 9 grams servos two for ailerons(one per each half of the wing) and two for flaps(one per each half of the wing), and at the field I only connect one wire, when hooking up wing, so there is no way I can mistake and wired wing servos in a wrong order. I also run 4 channel Rx with S.Bus output. It is great!

This is the S.Bus hub that I use

https://alofthobbies.com/frsky-sbus-cppm-decoder-with-pins.html
 
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Wayne

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That is a good setup. A little warning though, we do suggest you use digital servos with the decoders. The analogs may work for a while and then stop, or they may work fine forever..
 

ChrisAlbertson

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SBUS signals are meant to go to a Flight Controller (FC). Assuming it is an airplane you are controlling then yes you can do without an FC and send the sick positions directly to the servos.

Flight controllers typically have several flight modes. Like "altitude hold" heading hold and so on. like the autopilot on a typical general aviation aircraft. But one of the flight modes is "rate" and this just maps the sticks to the servos and you fly manually. (but maybe with a curve introduced if you like)

If you want an SBUS servo then what you do is buy a flight controller. These typically cost about $30 and have 6 outputs that could be connected to servos. .

Then you also gain all the fancy flight modes, So you can fly like an airline pilot, punch in a GPS waypoint and altitude and then go to sleep.

What do you gain by using SBUS? It is accurate but also the SBUS receivers are full duplex so you can't telemetry from the airplane. For exaplnme received signal strength and fuel/battery level. The FC can also record "everything' to a "black box" which might be an micro SD card. Anyone interested in airplane performance tuning wants this data

Some one asked if drones don't have servos to control a camera. They can. But if they do then the pilot is not driving the servos. They are controlled by the FC so as to keep the camera level as the aircraft does yaw, pitch or roll. This way the camera is stabilized. The operator just does pan and tilt

Bottom line is that if you want SBUS you can have it today but you need to buy a flight controller.
 
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Scott Page

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SBUS signals are meant to go to a Flight Controller (FC).

Serial Bus or S.bus has been around for quite awhile. Futaba introduced Sbus well before flight controllers were a thing. It's purpose was never intended for flight controllers - that use came much much later.

Sbus was introduced to allow a single receiver to control more higher voltage servos (than previously) with less wires and was suppose to be more convenient that PWM systems of that time. In Futaba's words "Imagine using one cable and one receiver to control up to 16 servos. Imagine being able to plug in battery packs anywhere you want. Imagine a system that simplifies setup, yet gives you more programming power at the same time."

It was viewed as the next great revolution in Transmitter/RX technology - however was never widely understood, trusted, or adopted by fixed wing hobbyists in general,. Until today only the largest fixed wing systems utilize S.Bus (as a rule). A decade ago Futaba was pressing for S.bus to be the next great revolution as a fixed wing solution. To see Futaba's vision see this great video from 2010.
The Sbus system floundered in relative obscurity until helicopter FC's finally took advantage of the technology. Early drone flight controllers used PWM connectors until just a few years ago.

While Futaba developed S.bus, they never caught on that S.bus would be ideal for the burgeoning drone market and missed capitalizing on that market by marketing a flight controller - however they have about 30 different S.bus servos on the market. This is somewhat ironic since they had what were arguably the most trusted (and expensive) gyros in the early days.

It seems to me that while Futaba may have developed S.bus; ultimately it's been FrSky that has capitalized on it and brought it to the multi-rotor community. I might be wrong about that - but I guess I'd really need to know how many of the 700,000 "drone" pilots (in U.S. A) are using Futaba vs. FrSky. Heli's on the other hand still tend to bend toward Futaba, but their numbers have always been a minority and have shrunk considerably the past few years.
 

Wayne

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No need to use a flight controller, but it is an option! Plenty of decoder options and most power management systems support Sbus to PWM conversion also.

Futaba made the price of working with Sbus very high. FrSky made it nearly FREE on their receivers. To buy an Sbus receiver from Futaba meant to got to pay them an extra $40 or so just to have the output available. Then you needed decoders and or spendy servos. It ended up being a very expensive option. Far cheaper to deal with some extra wires on the model, and that is what everyone knew and trusted anyhow.

Still to this day, Sbus use is very limited on fixed wing models.

-Wayne
 
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