Reversing the blades made no appreciable difference, helping to convince
me that the speed is too low.

I then bumped up the speed to 80% throttle (problem here, see below)
and at that point right rudder indeed caused a little yaw to the left.

I've got my rotor blade pitched mixed with throttle such that from
50% throttle to 100% throttle it goes from 0deg pitch to 12deg pitch.
I suspect that may be too agressive, as I'm taking off before I have
full rudder control.

What do you guys use for a throttle/blade pitch mix line/curve?

Thanks

Ehud