Ultimate upgrade for the 9398 4x4 crawler with pendulum steering (no servo needed). I also made a pendulum steering file in the rebrickable link you can download and have a closer look
LEGO MOC RC Buggy 9398-C by Cfachini | Rebrickable - Build with LEGO
LEGO 4x4 Crawler Set 9398 Brick Owl LEGO Marketplace
Lego Technic Model Off-Road Set 9398 4 x 4 Crawler 100% complete+instr.+box 2012 | eBay
LEGO Set 9398-1 4 x 4 Crawler (2012 Technic) | Rebrickable - Build with LEGO