I have a FLM cup F/R and the ring gear comes with it,so does pinion.I havent had problems with those cups and i have ran maxx with 4S&20XL06/07 motors.
I ran with stock cups when i had novaks hv 4.5 set on it,no problems.
if you want to go with robinson gears check out maximizer r/c products (the beadlock people) they have aluminum cups and your choice of robinson or traxxas gears
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It's "Dr. _paralyzed_" actually. Not like with a PhD, but Doctor like in Dr. Pepper.