unable to access E1-4 for sbus input using BBBW with Robotics Cape and Ardupilot

as it says, I have a BBBW with a Robotics cape, I configured pretty much as per the ardupilot blue setup....everything works fine except I cannot receive RC SBUS input on any E1-4.....i have tried many different kernels and images, librobotcontrol, etc....nothing seems to help....copy of uEnv.txt below, neither commenting or uncommenting the PRUSS options or cape overlay options makes any difference....the receiver and wiring check out ok, no probs there.

#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.19.142-bone-rt-r56
#uuid=
dtb=am335x-boneblack-wireless-roboticscape.dtb
###U-Boot Overlays###
###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays
###Master Enable
#enable_uboot_overlays=1
###

###Overide capes with eeprom
#uboot_overlay_addr0=/lib/firmware/.dtbo
#uboot_overlay_addr1=/lib/firmware/.dtbo
#uboot_overlay_addr2=/lib/firmware/.dtbo
#uboot_overlay_addr3=/lib/firmware/.dtbo
###

###Additional custom capes
#uboot_overlay_addr4=/lib/firmware/.dtbo
#uboot_overlay_addr5=/lib/firmware/.dtbo
#uboot_overlay_addr6=/lib/firmware/.dtbo
#uboot_overlay_addr7=/lib/firmware/.dtbo
###

###Custom Cape
#dtb_overlay=/lib/firmware/BB-I2C1-00A0.dtbo
#dtb_overlay=/lib/firmware/BB-UART4-00A0.dtbo
#dtb_overlay=/lib/firmware/BB-ADC-00A0.dtbo
###

###Disable auto loading of virtual capes (emmc/video/wireless/adc)
#disable_uboot_overlay_emmc=1
#disable_uboot_overlay_video=1
#disable_uboot_overlay_audio=1
#disable_uboot_overlay_wireless=1
#disable_uboot_overlay_adc=1

###PRUSS OPTIONS
###pru_rproc (4.14.x-ti kernel)
###uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-14-TI-00A0.dtbo
###pru_rproc (4.19.x-ti kernel)
##uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo
###pru_uio (4.14.x-ti, 4.19.x-ti & mainline/bone kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo

###Cape Universal Enable
#enable_uboot_cape_universal=1

cmdline=coherent_pool=1M net.ifnames=0 rng_core.default_quality=100 quiet