Are you using a stock henglong radio ? If so there's a couple things you can check , I'm sure Mike told you this already , I assume your running a rx18 board , does it have a internal receiver or external , with an antenna ? If you just changed the board only with an external board , problem could be in receiver if problem occurred when you dropped it, might have slight crack in it , if you still had screwed into lower chassis, also poor connection at 3 wire plug end into board can cause this , onto to the radio , your right controller has 2 reostats on each side of right hand stick , after taking back cover off , you will see them , check the metal contact sliders for contact , dirty etc , sometimes they metal slider will break off plastic end of your stick movement, then will stay in one spot until you jiggle it , then it will go into its normal spot until you move it again , just check everything inside carefully, I've ran into all these problems so far , and managed to fix most of my wonky tanks by checking these things , hope this helps