[Mesh] mesh routers can't opkg install kmod-usb-acm

i'm trying to use a mesh router to operate a duck coop door, and this means i want the USB port to recognize an ACM serial port. This is a normal thing for openWRT and usually works thusly: opkg update # downloads opkg package lists to /tmp opkg install kmod-usb-acm # installs a kernel module for ACM serial USB devices unfortunately, there are some problems with present mesh node firmware (including a node that was flashed in December 2015 and another which was flashed recently) and this process doesn't work. for starters, the opkg.conf on mesh nodes is messed up - i'm not sure why but there's a github issue here: https://github.com/sudomesh/sudowrt-firmware/issues/108 to get "opkg update" to work, follow the instructions in the first comment. That works for me, but when i do "opkg install kmod-usb-acm" i get the following error: # opkg install kmod-usb-acm Installing kmod-usb-acm (3.18.23-1) to root... Downloading http://downloads.openwrt.org/chaos_calmer/15.05.1/ar71xx/generic/packages/b…. Collected errors: * satisfy_dependencies_for: Cannot satisfy the following dependencies for * kmod-usb-acm: * kernel (= 3.18.23-1-b2f200610f46d20ef52d269421369d0c) * * opkg_install_cmd: Cannot install package kmod-usb-acm. # uname -a Linux jerkey-tl-wdr3500-2 3.18.23 #1 Fri Dec 25 00:14:49 EST 2015 mips GNU/Linux i have no idea what this error means or why it's happening, can anyone offer advice? thank you, -jake