I talked to him a while ago. The pinion cannot be made to fit a 6mm shaft; the tooth count is too low. He doesn't have the capability to make a compound bore. I have been working on other projects lately, the Berg 2.2 being one of them. I'll need to buy another suitable motor with a 5mm shaft, then get the pinion for it. I'm still "working" on it but I don't have any further updates.
just shave the shaft of the kb. grip it tight with some sandpaper, run it, and check often for fit. people have also used a dremel cut off wheel, ran the motor and moved the wheel up and down the shaft until a pinion fit. people are always afraid to grind on shafts, which perplexes me. they'll launch the motor off a ramp at 60mph, but won't grind that precious shaft! it's just a hunk of metal, it won't even get mad at you!
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It's "Dr. _paralyzed_" actually. Not like with a PhD, but Doctor like in Dr. Pepper.