What a fortuitous topic for me just now...
I finally have all the pieces and $ to get this NuVinci Dev Kit hub on my bike, the wheel goes to the shop tomorrow to get laced in.
It needs 12V and I have this new SLA battery.
Nominal Voltage . . . . . 12.0 v
NominalCapacity . . . . . 4.5 Ah, 4500 mAh
Max.Charging current . .. 1.35 A
Max.Discharging current . 67.5 A max
Dimensions 90mm(3.55") x 70mm(2.76") x 101mm(3.98") (LxWxH)
Weight . . 4 lb (1814 g)
Terminal . T1
$16 +SH
And got in this little 12V 6W 'tire rub' generator to put on the bike so it is time for little engineering for the Gen drive.
That little plastic 'rub gear' is 2cm in diameter, and the shaft to mount it on just 3mm to hold the 'gear' with the nut on flush with the end of the shaft.
Like you I have heard trying to run it rubbing against a 26" wheel at 40 MPH will toast it. Make sense since 15 MPH is about all I figure they are made to handle.
That means a gear reduction on the Gen, be that rubbing it against a small disc like the size of a disc brake disc or making the 'rub wheel' a lot bigger.
What do you think about putting a derailer gear on it and putting it in-line with the chain drive?
Those little gears are about the same size and I think wouldn't help much on a direct drive system as the chain is geared for reduction at the wheel, but I'm jackshafting and going the other way.
Thoughts?