I could see the prop spin once armed (I am arming using the mavros service client). The mode was set to POSCTL. I was sending the following in the OverrideRCIn msg:
channels =[1500, 1500, 1500, 2000, 65535, 65535, 65535, 65535]. (roll,pitch,yaw,throttle, switches). The first four values are mapped to my joystick with values between 1000 and 2000. The first three are equal to 1500 when the sticks are neutral, and the throttle is at 1000 when the stick is neutral.