I am using R12DS receiver and AT10II transmitter in my Autonomous Ground Vehicle. When I am trying to move the robot in forward and backward direction, it is not moving. I mean the motors are not rotating simultaneously. But for left-right direction movement issue, it moves normally. I have checked in the mission planner that transmitter throttles send signal but it is not working, I have tested this with FrSky transmitter-receiver and same thing is still going on. I have also tested changing the throttle of the transmitter. What should I do now or what thing that I need to check now?