yaw torque in quadcopter off by 1000x

[tridge]

I've been testing the quadcopter model as a backend for ArduPilot. I do have it flying now, but I had to change the mass of the propellers to be 1000x smaller than the current value in the urdf. The default mass of 0.005 seems reasonable, but I needed to change it to be 0.000005 to get reasonable yaw control. There is some gross mis-match between thrust and yaw torque on the propellers.
I suspect it is related to thrust for gazebo normally being on -1 to 1 scale, whereas for this model it is 0 to 1000 scale.