My project/robot is this. I'd like to make a camera dolly motorized at variable speeds. The dolly would be on some type of dolly track, weighing no more than 50lbs. and need to move slower than faster (no more than 5mph).
That's where people got you wrong, you didn't tell them what a dolly is.
If you do it with a wire, you have the advantage of less mechanical noise travelling to the mike(s) on the cam, but... You would have to deal with the wire on and on. I guess your mixer/producer will be able to filter out any kind of repetitive noise (if any should get on your lines) and personally I'd go with a dolly mounted motor and battery, controlled by the camera guy, but hey, lots of pros and cons either way, so it's a matter of personal taste.
I assume you allready use the tracks with a human powered "motor" now?
This person could tell you something about how hard it is to push, but if it's a real macho dolly (pun very much intended), or even a crane, perhaps it's a two+ person mover.
Talk to those that pushes it now and return with their answers (and perhaps if you know the weight of it), then you might get a more specific answer to sizing the motor power-vise.
Gee, the days when I was in TV broadcasting myself