Something I whipped up in a couple minutes on PAINT.

[color:"red"]Aluminum bars clamp to Cat-Trax axle and have a hole for a pivot bolt where they join [/color]
[color:"blue"]Power Frame. Holds the drive-tire, the [/color] [color:"green"]battery[/color], [color:"blue"] and the [/color] [color:"yellow"] electric motor (most likely a car starter-motor. [/color]
[color:"blue"]The light-blue bars are the handle-bars that the person can use to steer with. They way they are mounted also gives the person a solid place to push from to help this contraption along (especially if the battery or motor dies). [/color]
[color:"purple"]Battery cables. One grounds to the [/color] [color:"blue"]Power Frame[/color] [color:"purple"] while the other goes to a relay mounted on the [/color] [color:"blue"]Handle Bars[/color] [color:"purple"] The relay has two small wires that run to a small switch on the end of the [/color] [color:"blue"]Handle Bars[/color] [color:"purple"] and one large wire (activated by the relay) that powers the [/color] [color:"yellow"] electric motor. [/color]



I think I made that about as clear as mud, but how does this compare with what you're designing for 'Dune Dog'?

Using the biggest drive tire possible will get you the most contact patch and the fastest speed. A car starter motor will have plenty of power to spin the tire.