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The first big front wheel rollerblades.
http://www.flickr.com/photos/27532210@N04/2565924423/
So far, this is my best attempt:
http://www.flickr.com/photos/27532210@N04/2891204762/
(click on "mvxedwwwwi's photostream" for other views)
The problem with that one is the motor sits too low to the ground,
and it's not momentarily removable (that probably could be fixed).
But it rocked for propulsion, driving the two center wheels of a
four wheel skate worked great.
The possibilities seem limitless, and I'll keep trying. Lithium ion
battery technology is coming of age, and likely we are in for some
serious battery technology improvements in the foreseeable future
given the current energy crisis. Improvements in battery technology
will significantly help skating propulsion technology. Meanwhile, my
main design problem is keeping the motor far enough off of the
ground so that it doesn't catch on things. That means if I want to
drive a wheel at its axle, the wheel has to be large. If I want to
use a roller against a wheel like in the pictures linked to above, I
can sit the motor roller on the top of a single wheel. Gearing or
using a belt are other possibilities I haven't tried, partly because I
do efficiency.