PixHawk 2.4.8, Spektrum AR620, and Copter 4.0.7

[djsn (Douglas Johnson)]

I have trying to connect a Spectrum AR620 receiver to a PixHawk 2.4.8 running Copter 4.0.7 with no luck. It never appears in the APM Planner v2.0.29-rc1 Radio Calibration.

I originally connect it to the SPKT/DSM port, but that didn’t work. After reading

Pixhawk, PPM module and RC receiver power up issue

Andy, I was able to test fight today and everything appears to be working. Except I logged this error: PreArm: Internal errors 0x400 l:269 ,cnstring_nan while trying to armed it. After a reboot I didn’t experience any other problems and I was able to armed the Quad using the switch option since I cannot armed by holding throttle down and roll right for 5 seconds. I’m trying to tune it now which will be a challenge because of the setup I’m using. I’ll do more test tomorrow once I can set pr…

I moved it to the serial4/serial5 ports. The wiring is:

Serial pin 1 (Vcc) to AR620 slot 1, middle pin (+)
Serial pin 6 (GND) to AR620 slot 1, bottom pin (-)
Serial pin 2 (TX4) to AR620 slot 1, top pin (S)

I set SERIAL4 parameters:

SERIAL4_BAUD: 1152
SERIAL4_OPTIONS: 4
SERIAL4_PROTOCOL 23

Various posts suggest SERIAL4_OPTIONS should be 2 so I’ve tried that, too.

Still no joy. The Rx powers up and binds. Per that post above, I’ve tried powering the Tx both before and after the PixHawk. Neither works.

I plug a servo directly into the Rx port 2 and it moves with one of the joysticks.

Any help would be appreciated.
Thanks,
Doug

[andyp1per]

Only works on ArduCopter 4.1

[djsn (Douglas Johnson)]

Do the wiring and parameters sound correct?
Thanks,
Doug

[djsn (Douglas Johnson)]

I’ve downloaded 4.1.0 and still no joy. I’ve tried the spkt/dsm port and the serial port as described in above message, trying SERIAL_OPTION 4 and 2.

Thanks,
Doug

[andyp1per]

The baud rate needs to be 115
You also need to set RC_PROTOCOLS to be SRXL2 only. The other options sound correct.

[djsn (Douglas Johnson)]

No joy.

RC_PROTOCOLS: 8
SERIAL4_OPTIONS: 2 (tried 4, too)
SERIAL4_PROTOCOL 23
SERIAL4_BAUD: 115

AR620 is powered up and bound – the bind LED is lit.

The firmware upgrade screen is showing this device data:
Description: fmuv2
Manufacturer: ArduPilot
Vendor-Ident.: 0x1209
Product-Ident: 0c5741

Many thanks for your help.
– Doug

[andyp1per]

SERIAL4_OPTIONS needs to be half-duplex - so 4. (it’s also worth trying 12, just in case you have RX and TX the wrong way round).
RC_PROTOCOLS is a bitmask, so bit 8 (SRXL2) == 256
Finally, this RX will switch to PWM if it doesn’t receive a bootstrap request within 200ms of connection/power up. So you need to power up the flight controller first before switching on your transmitter.

Oh and the firmware on the AR620 needs to support SRXL2. If you bought it recently it should, if you got it a long time ago, maybe not. Upgrade requires a special cable.

[djsn (Douglas Johnson)]

Hurray! It works!

In summary for any that want to do this:

It works with Copter 4.1.0 connected to the serial4/serial5 ports. WIth the “Pixhawk” label upright and the arrow down, the pins are numbered from left to right.

The wiring is:
Serial pin 1 (Vcc) to AR620 slot 1, middle pin (+)
Serial pin 6 (GND) to AR620 slot 1, bottom pin (-)
Serial pin 2 (TX4) to AR620 slot 1, top pin (S)

The following parameters must be set in the Ardupilot->Config/Tuning->Full Parameter List
SERIAL4_BAUD: 115
SERIAL4_OPTIONS: 4
SERIAL4_PROTOCOL 23
RC_PROTOCOLS: 256

The flight controller must be powered up before turning on the transmitter. Apparently, older AR620 need to have a firmware update to support SRXL2. Mine is a couple of years old and works fine.

Many, many thanks. My 12 year old grandson is building a drone and this has stumped us both. The Spectrum manual is worthless and their website is worse.

– Doug