I finally managed to test the motor and "measure" the RPM.
I pushed the shaft against the rear wheel of the bike and checked the revolutions the rear wheel took under a minute. Seems like with this load (bike off the ground, practically minimal load) the motor spins with 1950 RPM.
Electictracer, I have similar doublts about the angle grinders. Checked RPM/Torque data and found out, that they produce like a 5th of the torque I might use as continous...
I happen to have some leftover parts from a motorbike gearbox, so in theory I can can put together a reduction gear which can do the trick...
the data I have so far:
Motor RPM (minimal load): 1950
Bike wheel RPM @ 20km/h : 160
reduction gear I can make with the gears available: 19/12: 1:1.58
big question: what RPM would the motor have, provding enough torque for a continous motion with the speed of about 20km/h? If no load RPM is 1950, with what RPM would I have to count for the gears?
With this site
Bicycle Speed (Velocity) And Power Calculator
I calculate 100W-s for my humble carcass on the frame, 0% incline.
1%: 180W
2%: 260W
0% - 260W ---> 28km/h
Of course I do not know the accuracy of the site but it gives a good idea. I'll be able to play with the final gear ratios as it will be with stock rear sprockets, so I'll figure it out.
Any ideas about the RPM under load for such a motor?