Engine RPM 2000, engage red lever slowly until engine rpms drop down to 1300 to 1350 (engine sounds like it wants to quit) and stop engagement, let rotors catch up until around 85-95rpms and then you should be able to engage all the way down. Now you can slowly add throttle, at 100 RPM you can pull stick back to neutral and at 130rpm go full aft. around 2700 you should be seeing close/around 175rpm rotor rpms (do not exceed 3100 engine rpms). 175 rpm what I launch at as I am using a hard surface runway that is long and it is plenty.
Following this technique will prevent the belt from slipping and heating up and melting the 3D printed part.
PS - you should or will feel the stick pull right some, make sure you center stick before launching or you will drift right.
This is what I am doing based on some discussion with Fusioncopter, please share your technique/experiences so we can all learn.
Very similar method-
*slowly engage pre-rotator and gently throttle up to maintain 2000erpm
*at about 2000/120rpm prerotate is fully engaged and engine/rotor synched- you can hear when it does
*progressively increase throttle to about 3000/175 and we are ready to roll!
*stick back, brakes off, disengage pre-rotate and away we go!
I can't get more than about 170-175rrpm, but that is fine for me.
If the brakes slip, a bit of back stick above 120rrpm.
One gotcha- make sure your brakes disengage.
I fly from a grass strip, and one take-off took a bit longer that normal to get airborne.
It wasn't until my downwind landing checks that I noticed the brakes were still engaged!
I checked the take-off wheel tracks and confirmed the rear wheels skidded along in the wet grass.
I now unlock and manually hold the brakes during pre-rotate, as things get a bit busy during the initial takeoff run- not a good time for unexpected surprises!