Sorry if this is a silly question, or already asked and I missed it, but I was looking at the ERP page, and admiring the engineering that went into it. one thing that I'm confused about. On the servo list it says it uses HS-225BB x 2 (wheels) servos and I looked at servo city at their list of servos that can and cannot be modified for continuous rotation, and they say the HS 225BB is not modifiable, but a similar servo HS-225MG is able to be modified. What's the difference between a BB and an MG servo?