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Futaba and FrSky SBUS - Printable Version

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Futaba and FrSky SBUS - flyingw - 09-22-2024

Jim,

I "learned" (just internet so I do not know how reliable the information is) that Futaba's SBUS uses 3.3v or 5v to represent a zero logic value in the bitstream and ground as a logic one in the bitstream.

FrSky's SBUS uses the opposite:  They have ground as a zero value and 3.3v or 5v as the one value.

In my experiment where I fed SBUS to the X10+v2 from an FrSky receiver, the old analog servo did not work, but the digital servo worked.  When I fed the X10+v2 SBUS from a Futaba receiver, both the old analog and the digital servo worked.

We concluded that the frame rate used by FrSky was too fast for the analog servo.  Could it also have something to do with the FrSky SBUS voltages being opposite to that of the Futaba standard SBUS signal?

I had the X10+v2 configured to accept "Futaba SBUS" as the input (not the inverted choice).

Thanks for your opinion,

Paul


RE: Futaba and FrSky SBUS - XPS - 09-23-2024

Futaba uses inverted polarity serial data. Nobody else does. The XtremeLink products all support the proper inverted polarity so that the data is read correctly. That has nothing to do with the frame rate. The frame rate determines how often the servo's motor is powered on/off. This determines the holding force of an analog servo (it does not for a digital servo). If you turn the motor on/off too fast with an analog servo the motor circuitry can actually burn up because they are designed for a ~20ms frame rate.