I switch between OpenWrt and DDWrt often with my wr841nd v7 and wdr4900v2.
From DDwrt to OpenWrt:
- Enable SSH in services tab of ddwrt.
- scp (winscp) openwrt-your-router-FACTORY.bin (factory not upgrade) to /tmp
- ssh login to ddwrt, cd /tmp
mtd -f write openwrt-your-router-factory.bin linux
reboot
From Openwrt to DDwrt:
mtd write /tmp/factory-to-ddwrt.bin firmware