I recently invented and built a push stick for inline skating (and
maybe skateboarding). Some have already been built, but mine is
(probably) the first ultralight version that uses an automatic
gripping technique instead of static weight to hold the wheel
against the ground. Weighing only 6.5 pounds, when not in use it
can be easily carried instead of towed.

If you build stuff and can do light metalworking, it is easy to
make.

Parts...

.... DeWalt DW960 right-angle cordless drill

.... an aluminum pole/tube, about 4 feet

.... a 125 mm Razor scooter wheel

.... a battery holder and speed controller (mine taken from another
DeWalt cordless drill)

.... ten inch aluminum flat bar

Construction... The right angle drill goes on one end of the
aluminum tube, and the battery holder and the speed controller
goes on the other end. That's about it. The aluminum flat bar is
bent into an L shape and stuck on the aluminum tube with hose
clamps. The least easy part is grinding/shaping the chuck to hold
the scooter wheel. It can be made so that the wheel is held very
closely to the large bearing part of the right angle gear. That
was an easy method, but there are alternatives to mounting the
wheel. Like doing away with the chuck and using the arbor with a
bearing on the opposite side of the wheel, and adding a small
aluminum flat bar fork. I'm not sure how long the right angle gear
will hold up to the bending force of my current design, time will
tell.

Auto grip, how it works... As the push stick pushes, the L shaped
aluminum flat bar that is stuck on the aluminum tube presses
against your back thigh. As the push stick wheel rolls in closer
to your body, the counterforce of your body forces the wheel into
the ground and provides traction. It is like a wedge.

It takes some skill to use, but I am no spring chicken and it's
easy. Using the DeWalt 18 V right angle drill, the top speed is
only somewhere between 10 and 20 mph. But it is surprisingly
powerful, enough to push 160 pounds on inline skates up slight
hills. Using DeWalt XRP batteries, taking one spare battery is
more than enough for my needs. Individual needs will vary
radically.

For reference, here is an example of a push stick that uses a
handlebar.

http://www.youtube.com/watch?v=UKC5UjQXhFE

It is loud and bulky using a gasoline engine, but it is powerful
and fast. Notice the user in the video occasionally pushes with
his legs as he is rocketing along the ground. The pushing is just
ridiculous, it is simply to please the macho crowd who think that
you must push in order to be a real skater. Propelled skating is a
riot, and pushing has nothing to do with enjoying it.

One recreational use here for my Motail (motorized tail) will be
on a smooth and huge sloped parking lot in the neighborhood. I
zoom around and down, and on the final turn, I put the push stick
down and effortlessly zoom back up the hill for another go at it.

Hopefully the weight can be reduced from 6.5 to maybe 5 pounds,
without sacrificing any performance. Using a lithium-ion battery
(of course), a thinner wall aluminum tube (currently 1/16"), and
other minor changes.

Pics on my page.
http://www.flickr.com/photos/27532210@N04/

Good luck and have fun.