Hi,
I've got a Futaba T14SG transmitter and a R7008SB receiver and I wanted to test SBUS on paparazzi. R7008SB receiver has 8 channels, 1 sbus connector and 1 sbus2 connector. As long as I knew, sbus2 is for telemetry sensors, and the sbus port should send a datastream compatible with normal sbus servos and paparazzi sbus code. So it looked like the only problem was to invert the signal and plug it onto the uart.
I've put a signal inverter between the receiver and paparazzi and connected it to uart1 of lisa/M. I've got no signal at all. After trying different configurations on the airframe file, different circuits for the inverter, and even pluggin the receiver to an arduino to test some of the sbus libraries that are available around, nothing worked.
I started to look for more documentation about sbus, and the r7008sb receiver in particular, and found some interesting stuff. Someone in the multiwii forum posted an issue regarding this receiver and the different endbyte. I commented out the endbyte check in the paparazzi code and I started to receive sbus frames like a charm. I tested also that, as the multiwii formun says, if I put the transmitter in 12ch mode the endbyte is 0x08, but in the 14ch mode the endbyte changes. Digging up some more i found this and this, so looks like in the 14ch mode, the one that allows external telemetry sensors, the endbyte act as a counter to signal telemetry sensors their slot for transmission.
The weird thing is that actually this receiver (R7008SB) has two sbus ports, one labeled as "SBUS" and other labeled as "SBUS2". The manual says sbus2 port is for sensors and sbus port is for servos and products not compatible with sbus2, but the fact is that the protocol is a bit different. I don't have any futaba sensors to test in the bus either.
Another funny thing about this receiver, and i think other furaba sbus receivers, is that the channels are not filling the full range. I noticed when I connected the paparazzi and the rc couldn't reach full throw of the actuators. I can increase the endpoints in the transmitter or adjust ranges in the radio.xml file so there is no problem, but it is strange. I don't know if this happens also with other sbus receivers like frsky or orangerx.
Best Regards.
Miquel Ángel Torres Gil
Instituto Tecnológico y de Energías Renovables, S.A. (ITER, S.A.)
Polígono Industrial de Granadilla, s/n 38619 - Granadilla de Abona
Santa Cruz de Tenerife - España (Spain)TEL: + 34 922-747-700; FAX: +34 922-747-701
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