Gruber Assist is availble and buyable...
a Bikestore here in Vienna sells them..
2008 they were sold out, for 2009 they plan to increase the production by factor 2
its a setup for sport-bikers...
its VERY VERY light, so you don´t realy feel any negativ side-effects of the drivetrain
for the 100Watt -> don´t think that is that few...
i have a Bafang hub-motor
i have tested it with bikecontroller (currentlimit at 14A) and 36-48V which results in over 400Watt output
on a steep hill you get less than 100Watt to the wheel -> also when the motor can spin out in flat terrain you see 400-450Watt to the wheel with the same controller
look on the two graphics...
you can see: the higher the loads get (the amps go up), because of hill,
the more the controller has to limit the voltage, so the amps do not go over the controller set limit
positiv: the efficience stays relativley high, also when going up a hill...
the absolut lost Power (Watts) is not higher then when going fast, also the motor efficience is down
nevativ: on a hill you get a lot less power than it is possible when motor can spin fast
the gruber assist, optibike, Flyers, or bike-elektro-antrieb.ch can use the bikes gearing..
so also when going slow, the motor can still sturn fast, the controller still has not to limit the voltage...
for that: a hub-motor able to go 40km/h and putting out 400Watt will only put out maybe 100Watt when going up a hill with less than 10km/h
on the other side the bottom bracket motor can use the gearing (maybe 4:1), so can still put out the same power at 10km/h as he can do at 40km/h
and then a 200Watt Motor on a hill is stronger, than a 400Watt Hub (that puts only 100Watt out on the hill)
on the other side:
the maximum possible efficience of the gruber assist is not that high...
a 1:111 planetary gearing, then the 90° gearing --> that costs efficience
so it can never reach as high efficience as a hubmotor
on the other side: when a hub-motor drops way down under 50% the bracket motor can still be at his high efficience-spot
the little gruber-assist motor gives always the 100Watt to the wheel, because of the gearing
its made for going up hills, helping on climbing..
on slow speeds no 2000Watts are needed, 100W are already a good assistance !
for me a downside: gearnoise (and price)
for the freewheel: it has a freewheel (between planetary gearbox and 90° gear -> so the 90° gears are always turning, but than there is the freewheel
so when motor is off, you can drive the bike like a normal bike..
as said: this concept is for the real bikers, for athletes
not for daily-commuters who want to go fast without pedaling much to work...
another, stronger alternative:
http://www.bike-elektro-antrieb.ch