There's this, but it's not much and the designer/maker says this is
only a prototype, the real thing will not have any wood in it:
Inside the wooden (soon to be metal, I presume) wheelbearing case
are five metal gears - all three wheels are driven. I know this
because I was at the club meeting a few months ago when Dale showed
this off and took it apart. I'm not sure if I should divulge any more
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