A flat spot is a must no matter what. dont give it a second thought.

Is it better to make a flat spot on almost the whole motor shaft (like the motors that already have one) Or just a little spot?

Thats easy, the whole shaft. You never know when your gonna have to put a pinion on backwards or if its a fat one or skinny one, the set screw could wind up any where.

i agree its best to flat the whole shaft otherwise you will create a weak point in the shaft that would take most of the deflection under high lateral loads.

I'll shoot a pic of my flat spot later this day..

I use a dremel and a grinding stone.. Works like a charm. I try to make them a bit hollow..

I make a flat spot for most of the shaft, but I leave the end bigger, just in case the setscrew gets loose. That way the pinion can't go flying off

a keyway and a set screw would work best.. but that's a real pain in the *ss to do... too much work..

That's a pretty darn good idea Finnster! I know I recently had a pinion fly off on me... didn't wait long enough for lock tight to harden and/or I didn't tighten th set screw enough.

Yeah, that is a very good idea!

I've used the "dimple" method on my motors. If I took a photo you guys would laugh...it's a miracle the shaft hasn't broken given how deep I've drilled! Anyway for my next motor I want the flat spot. If any of you have the perfect method, post it, including any bit part numbers or whatnot. I'm happy to buy the right tool/bit.

Also, maybe as a value add, RC Monster could offer it for a fee with any new motor purchase - hint - hint...I'd certainly pay $10 extra to have it done right.

I use a grinding stone on the dremel and leave the last mm or 2 as well so the pinions can't come off. The pinion came loose once or twice with my fiegao, but I didn't loose the pinion because of the end being bigger.
With my neu I think I may have done the flat spot a bit better (still with the lip at the end though), because I haven't had a loose pinion in the last 6 months I've had that motor, I don't use loctite on the set screws.
I've put pinions on the shaft with the set screw facing both ways and the lip at the end hasn't gotten in the way.