@Zicong
Regarding using RC-100 communication protocol, the Dynamixel2Arduino library already has a example sketch called “RC100”:
If you need to flip-flop between the OpenCM-904 per se and the 485-EXP board, this post can be helpful to you:
Regarding BT-410 and RC-100B, I am assuming that you already have the BT-410 set of Master and Slave BT-410s? (BT-410 SET - ROBOTIS).