[EricH]

Window motors, at least of the type used in FRC, are not renowned for their speed. Just ask Billfred.

Admittedly, FRC window motors include wormdrive gearboxes, which are really not fast.

I was thinking that based on your size constraints and power needs, you might want to look into something along the lines of the FP or the RS-550 that we get in the KOP. Drill motors are about the same size (don't believe the size of the drill). If two drill motors can move 130 lbs at a decent speed by themselves, after being run through a standard planetary drill transmission, and not smoke themselves very often, I'd say they can probably assist a rollerblading human pretty well. (Pre-2005, one of the most common drivetrains in FRC was a pair of drill motors.)