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Sometimes pedalling just gets so tedious

I bought a starter motor for a Dodge truck from ebay and a couple deep cycle lead acid batteries from an online battery store.  I found a ratcheting sprocket that fit the shaft for the starter motor perfectly (dumb luck!) and attached a larger sprocket to the spokes of the left side of the rear wheel.  This was to preserve the ability to pedal if I had to.  Then I got a 12V coil contactor that was rated to 100A from Digikey.  Wire the whole thing up with a microswitch up on the handlebars and let her rip!

How did it go?

The first test was with the rear wheel elevated on the workbench.  The wheel spun up remarkably fast before throwing the chain off.  A few tweaks to the alignment and the chain stayed on.  The first road test also ripped the chain off.  The bending moment on the motor bent the whole motor mount frame downward enough to mis-align the chain.  I tried beefing it up but the mount just wasn't strong enough.  By now the motor was starting to overheat - it turns out that starter motors just can't handle continuous loads.

I threw away most of the components of this bike but saved the batteries and charger.