That's what I ended up putting into this contraption. I built it up for the fun of it, without a plan really. It's more fun to have a shell of an idea, a basic understanding, and just dive into it. Thanks to Varnum for his input on the centering of the rollers (28cm/83.2cm) and to Goodwill for selling used Rollerblades for $5.00, and to the Chinese for crating their furniture in solid lumber (usually better wood than the furniture inside of the crate) and to the guys in our shop at Redeker's for their tech support and just letting me use the tools and shutting up about how crazy I must be! They know...
Each roller is a pair of Rollerblade wheels screwed into the ends of a 12" piece of 3"i.d. PVC. I used washers as spacers because the wheels are only 77mm, short of the 3" inside diameter.
The two forward rollers have a granny gear bolted to a wooden spacer, which is then screwed into the solid center of the Rollerblade wheel. Added some Delrin spacers to take out the side to side slack and equalize the pressure.
Slipped the chain around the granny gears and DAMN! there's too much slack. Can't take out a complete link, so I fabbed up a chainwheel roller. Adjustable if I ever run a smaller wheel on it. Actually, there is enough off-center in the way I drilled out the wooden adapter for the grannys (like an ENO hub, kinda) that I could play around and probably get the chain tension to work, but I wanted to ride it soon, so I just did a stop-gap fix for now.
I "rode" it in my basement today and I don't know, it's pretty squirrely on this thing! I was not able to master it yet, but it works if I have something to hold myself up! I consider myself better than average in bike handling skills, and slippery mud/ice is no problem, but this is wild! I'll have to take it outside and learn to ride it where I won't brain myself on a water heater or stairwell stringer if I fall. Besides, my wife will kill me if I die in the basement!? If I master it, I will take it all apart and stain it up. Then hang it on a peg and forget about it! My next project is a replica of an 80's era "brick" cell phone shell that I can slide my Motorola into and take "Retro" to a new level (lower, but new) Later! Travel Gravel!