EPM Gripper on PX4?

I have a standard hexacopter that is equipped with an EPM Gripper on the Aux 1 port. I can get it to work manually perfect like butter. My problem is how do I do it in mission mode? I have tried the “do set servo” command to the desired PWM setting on servo 1, but I cant get the device to work. I am sure it is a simple setting but I am baffled…