Are you just using a Heng Long stock radio. IF you are then your options are very limited. IF you went with a DBC you could keep your current RX 18 for turret functions and buy a sabre tooth for about 70 bucks that can handle the drive motors. You would have to use a servo wire splitter cabe so you could run to the sabre tooth board and to the RX 18. Plug your motors into that and you should be laughing. I haven't done this yet buy was lookng at the Sabre tooth ESC just the other day. It should work.

Again you will need a DBC so you can use a standard receiver to go to the Sabre tooth, and of course if you go with a DBC you might as well get the DBC3 as it can mate up with a Benedini sound card when you want sound.

[link=http://www.robotmarketplace.com/products/0-SABER2X12-RC.html]Sabre tooth[/link]

Cheers