Blown Transmission
< < < Serious big time trouble for this bike. > > >
The entire rear end of the frame was custom designed (many hours) so as to make the Sturmey Archer 8-Speed operate perfectly. I had all kinds of special things like a clamping dropout for the slotted rear axle.
So today I get the motor together and everything to go with it. I'm running 48 volts and 40 amps so the torque is very impressive... apparently too impressive for the hub. I managed to ride around a little and the bike was doing pretty well, except any time I really torqued the motor the chain was still popping over it.
I stop... return home and place the bike in it's bike stand where the rear wheel can freewheel. In order to simulate some torque I would stop the motor and apply the rear brakes so as to stop the rear wheel. Then I let off the brakes and crank the throttle hoping to see whatever is going on with the chain.
But instead.... POP... the rear axle is broken.
The rear axle broke while the bike was in the bike stand !!!
So the motor had enough torque to actually break the axle. (and I don't have to worry about any other possible cause) The reason is that while the axle and hub look really strong on the outside, you can see that the axle on the inside has all kinds of deep grooves in it that weaken it. (well, the picture is probably not good enough, but take my word for it, the axle has deep grooves for little clicker thingies) The axle would never have survived.
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This means a complete redesign of the rear end. No more internally geared hubs, they are expensive ($125) and fragile and it's hard to get good shifts with them because they require you to let off the power. The derailler can handle all the torque you can throw at it and it can be shifted while under power.
This probably sets me back a month.
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It's somewhat ironic that when I do get some better power out of the motor that it's the motor that manages to break something else.